ZJ BRAKES 5-1 BRAKES CONTENTS page pageABS BRAKE DIAGNOSIS . . . . . . . . . . . . . . . . . . . 3 MASTER CYLINDER—BRAKE BOOSTER—ABS SYSTEM OPERATION . . . . . . . . . . . . . . . . 10 COMBINATION VALVE—HCU . . . . . . . . . . . . . 18BRAKE FLUID—BRAKE BLEEDING— PARKING BRAKES . . . . . . . . . . . . . . . . . . . . . . . 51 BRAKELINES/HOSES . . . . . . . . . . . . . . . . . . . 15 REAR DISC BRAKES . . . . . . . . . . . . . . . . . . . . . 41BRAKE PEDAL AND BRAKELIGHT SWITCH . . . 61 SERVICE BRAKE DIAGNOSIS . . . . . . . . . . . . . . . 4DISC BRAKE ROTOR SERVICE . . . . . . . . . . . . . 48 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . 63FRONT DISC BRAKES . . . . . . . . . . . . . . . . . . . . 33 SPEED SENSORS—TONE WHEELS—GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1 ACCELERATION SWITCH—ECU . . . . . . . . . . . 29 GENERAL INFORMATION INDEX page pageABS Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Brake Warning Lights . . . . . . . . . . . . . . . . . . . . . . . 2Brake Changes for 1995 . . . . . . . . . . . . . . . . . . . . . 1 Brakelining Material . . . . . . . . . . . . . . . . . . . . . . . . 2Brake Fluid/Lubricants/Cleaning Solvents . . . . . . . . . 2 Parking Brake Mechanism . . . . . . . . . . . . . . . . . . . . 1Brake Safety Precautions . . . . . . . . . . . . . . . . . . . . 2 Wheel Brake Components . . . . . . . . . . . . . . . . . . . . 1WHEEL BRAKE COMPONENTS BRAKE CHANGES FOR 1995 All Grand Cherokee models are equipped with A different master cylinder, power brake booster,power assist four-wheel disc brakes. Antilock (ABS) and HCU are used in the 1995 Grand Cherokee ABSbrakes are also standard equipment on all models. system. Single piston, disc brake calipers are used front The master cylinder reservoir has a single filler capand rear. Ventilated disc brake rotors are used at the and is no longer interconnected with the HCU. Thefront and solid rotors are used at the rear. new HCU has built-in accumulators. The pedal travel Power brake assist is supplied by a vacuum oper- sensor has been eliminated which means the powerated, dual diaphragm power brake booster. brake booster is different as a result. The master cylinder used for all applications has The rear disc brakeshoes and caliper bracket arean aluminum body and nylon reservoir with single new for 1995. The bracket ledges are machined to ac-filler cap. commodate the changed brakeshoes. The outboard A combination valve is used for all applications. brakeshoes now have anti-rattle springs and the in-The valve contains a pressure differential switch and board shoe has a wear warning strip attached.rear brake proportioning valve. The rear disc splash shield is now secured to the caliper bracket with two factory installed rivets. Al-ABS BRAKES though the rivets have to be drilled out to separate The antilock system is an electronically operated the shield from the bracket, the rivets do not have toall wheel brake control system. The system is de- be replaced afterward. Refer to the service proce-signed to prevent wheel lockup during periods of dures in the parking brake section.high wheel slip when braking. The antilock electronic control system is separate PARKING BRAKE MECHANISMfrom other electrical circuits in the vehicle. A sepa- The parking brake mechanism consists of a cablerate electronic control unit (ECU) is used for the ABS operated, dual shoe, drum brake mechanism. Thesystem. brake shoes operate within a drum cast into the rear disc brake rotor. The shoes are mounted on a splash
5-2 BRAKES ZJshield attached to the caliper bracket and rear axle CAUTION: Never use gasoline, kerosene, methyl ortube flange. Parking brake adjustment is controlled isopropyl alcohol, paint thinner, or any fluid con-by a cable tensioner mechanism. taining mineral oil to clean the system components. These fluids damage rubber cups and seals. If sys-BRAKE WARNING LIGHTS tem contamination is suspected, check the fluid for All Grand Cherokee models have two brake warn- dirt, discoloration, or separation into distinct layers.ing lights. A red light is used for the service and Drain and flush the system with new brake fluid ifparking brake system. An amber light is used for the contamination is suspected.ABS system. Both lights are in the instrument clus-ter. The red light alerts the driver if a pressure differ- BRAKE SAFETY PRECAUTIONSential exists between the front and rear hydraulicsystems. The red light also alerts the driver when WARNING: ALTHOUGH FACTORY INSTALLEDthe parking brakes are applied. BRAKELINING ON GRAND CHEROKEE MODELS IS The amber antilock light only illuminates when an MADE FROM ASBESTOS FREE MATERIALS, SOMEantilock system fault occurs. AFTER MARKET BRAKELINING MAY CONTAIN AS- Both lights illuminate for about 1-2 seconds at en- BESTOS. THIS SHOULD BE TAKEN INTO ACCOUNTgine start; this occurs as part of a normal bulb check. WHEN SERVICING A VEHICLE WITH PRIOR BRAKE SERVICE. WEAR A RESPIRATOR WHEN CLEANINGBRAKELINING MATERIAL BRAKE COMPONENTS AS ASBESTOS FIBERS CAN Factory installed front and rear brakelining on BE A HEALTH HAZARD. NEVER CLEAN BRAKEGrand Cherokee models, is made from organic mate- COMPONENTS WITH COMPRESSED AIR. USE Arials combined with metallic particles. The brakelin- VACUUM CLEANER SPECIFICALLY DESIGNED FORing material does not contain asbestos. REMOVING BRAKE DUST. IF A VACUUM CLEANERBRAKE FLUID/LUBRICANTS/CLEANING SOLVENTS IS NOT AVAILABLE, CLEAN THE PARTS WITH WA- Recommended brake fluid is Mopar brake fluid, or TER DAMPENED SHOP RAGS. DO NOT CREATEequivalent meeting SAE J1703 and DOT 3 stan- DUST BY SANDING BRAKELINING. DISPOSE OFdards. ALL DUST AND DIRT SUSPECTED OF CONTAINING Use Mopar multi-mileage grease to lubricate drum ASBESTOS FIBERS IN SEALED BAGS OR CON-brake pivot pins and rear brakeshoe contact points TAINERS. FOLLOW ALL RECOMMENDED SAFETYon the support plates. Use GE 661 or Dow 111 sili- PRACTICES PRESCRIBED BY THE OCCUPATIONALcone grease, or multi-mileage grease on caliper bush- SAFETY AND HEALTH ADMINISTRATION (OSHA)ings and slide pins. AND THE ENVIRONMENTAL PROTECTION AGENCY Use Mopar Brake Cleaner, or fresh brake fluid to (EPA), FOR HANDLING AND DISPOSAL OF PROD-clean or flush brake system components. These are UCTS CONTAINING ASBESTOS.the only cleaning materials recommended.
ZJ ABS BRAKE DIAGNOSIS 5-3 ABS BRAKE DIAGNOSIS INDEX page pageABS Diagnostic Connector . . . . . . . . . . . . . . . . . . . 3 General Information . . . . . . . . . . . . . . . . . . . . . . . . 3ABS Warning Light Display . . . . . . . . . . . . . . . . . . . 3 Normal Operating Conditions . . . . . . . . . . . . . . . . . . 3Antilock ECU and HCU Diagnosis . . . . . . . . . . . . . . 3 Wheel/Tire Size and Input Signals . . . . . . . . . . . . . . 3DRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3GENERAL INFORMATION hicle wheels and tires should all be the same size The DRB scan tool is required for all ABS diagno- and type. However, the Jeep ABS system is designedsis. The scan tool is used to identify ABS circuit to function with a compact spare tire installed.faults. Once a circuit fault has been identified, refer to the NORMAL OPERATING CONDITIONSappropriate chassis/body diagnostic manual for indi-vidual component testing. Sound Levels The hydraulic control unit pump and solenoidABS WARNING LIGHT DISPLAY valves may produce some sound as they cycle on and The amber antilock light illuminates at startup as off. This is a normal condition and should not be mis-part of the system self check feature. The light illu- taken for faulty operation. Under most conditions,minates for 1-3 seconds then goes off as part of the pump and solenoid valve operating sounds will not benormal bulb check routine. audible. An ABS circuit fault is indicated when the amberlight remains on after startup, or illuminates at any Vehicle Response In Antilock Modetime during vehicle operation. During antilock braking, the hydraulic control unit Verify that a fault is actually related to the ABS solenoid valves cycle rapidly in response to antilocksystem before making repairs. For example, if the electronic control unit signals.red light illuminates but the ABS light does not, the The driver will experience a pulsing sensationproblem is related to a service brake component and within the vehicle as the solenoids decrease, hold, ornot the ABS system. Or, if neither light illuminates increase pressure as needed. Brake pedal pulsing willbut a brake problem is noted, again, the problem is also be noted and is a normal condition.with a service brake component and not with theABS system. Steering ResponseABS DIAGNOSTIC CONNECTOR A modest amount of steering input is required dur- The ABS diagnostic connector is located inside the ing extremely high deceleration braking, or whenvehicle. The connecter is the access point for the braking on differing traction surfaces. An example ofDRB scan tool. differing traction surfaces would be when the left The connector is blue or black in color and is a side wheels are on ice and the right side wheels are6-way type. The connector is under the carpet at the on dry pavement.forward end of the console just under the IP center. Owner Induced FaultsDRB SCAN TOOL Driving away with the parking brakes still applied ABS diagnosis is performed with the DRB scan will cause warning light illumination. Pumping thetool. Refer to the DRB scan tool manual for test brake pedal will also generate a system fault and in-hookup and procedures. Diagnosis information is pro- terfere with ABS system operation.vided in the Chassis Diagnostic Procedures Manualfor Jeep Grand Cherokee Models. ANTILOCK ECU AND HCU DIAGNOSIS An ECU or HCU fault can only be determinedWHEEL/TIRE SIZE AND INPUT SIGNALS through testing with the DRB scan tool. Do not re- Antilock system operation is dependant on accurate place either component unless a fault is actually in-signals from the wheel speed sensors. Ideally, the ve- dicated.
5-4 SERVICE BRAKE DIAGNOSIS ZJ SERVICE BRAKE DIAGNOSIS INDEX page pageBrake Component Inspection . . . . . . . . . . . . . . . . . . 5 Low Pedal . . . . . . . . . . . . . . . . . . . . . .... . . . . . . 5Brake Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Parking Brake Diagnosis . . . . . . . . . . . .... . . . . . . 7Brake Fade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Pedal Falls Away . . . . . . . . . . . . . . . . .... . . . . . . 5Brake Fluid Contamination . . . . . . . . . . . . . . . . . . . 6 Pedal Pulsation (Non-ABS Brakes Only) ... . . . . . . 6Brake Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Power Brake Booster Check Valve Test .... . . . . . . 8Brake Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Power Brake Booster Vacuum Test . . . .... . . . . . . 9Brakes Do Not Hold After Driving Through Deep Preliminary Brake Check . . . . . . . . . . . .... . . . . . . 4 Water Puddles . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Rear Brake Grab . . . . . . . . . . . . . . . . .... . . . . . . 6Contaminated Brakelining . . . . . . . . . . . . . . . . . . . . 6 Road Test . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . 5Diagnosis Procedures . . . . . . . . . . . . . . . . . . . . . . . 4 Service Brake Warning Light Operation .... . . . . . . 5General Information . . . . . . . . . . . . . . . . . . . . . . . . 4Hard Pedal or High Pedal Effort . . . . . . . . . . . . . . . 5 Spongy Pedal . . . . . . . . . . . . . . . . . . . .... . . . . . . 5GENERAL INFORMATION (2) Check condition of tires and wheels. Damaged The diagnosis information in this section covers the wheels and worn, damaged, or underinflated tires canvehicle service brake components which include: cause pull, shudder, tramp and a condition similar to• disc brake calipers grab.• disc brakeshoes (3) If complaint was based on noise when braking,• disc brake rotors check suspension components. Jounce front and rear• parking brake mechanism of vehicle and listen for noise that might be caused• master cylinder by loose, worn, or damaged suspension or steering• combination valve components.• power brake booster (4) Inspect brake fluid level and condition. Correct• brake pedal and brakelight switch fluid level is to FULL mark on reservoir. Remember• red brake warning light that fluid level will decrease slightly as normal brakelining wear occurs. If fluid level is abnormallyDIAGNOSIS PROCEDURES low, look for leaks at calipers, wheel cylinders, brake- Service brake diagnosis involves determining if the lines and master cylinder.problem is related to a mechanical, hydraulic or vacuum (5) Check fluid condition.operated part. A preliminary check, road testing and (a) Fluid should be reasonably clear and free ofcomponent inspection are needed to determine a prob- foreign material. Note that brake fluid tends tolem cause. darken over time. This is normal and should Road testing will either verify proper brake opera- not be mistaken for contamination. If fluid istion or confirm the existence of a problem. Compo- reasonably clear and free of foreign material,nent inspection will, in most cases, identify the it is OK.actual part causing a problem. (b) If fluid is highly discolored, or appears to con- The first diagnosis step is the preliminary check. This tain foreign material, drain out a sample with ainvolves inspecting fluid level, parking brake action, clean suction gun. Pour sample in a glass containerwheel and tire condition, checking for obvious leaks or and note condition described in step (c).component damage and testing brake pedal response. A (c) If fluid separates into layers, or obviously con-road test will confirm or deny the existence of a prob- tains oil or substance other than brake fluid, sys-lem. The final diagnosis procedure involves road test tem seals and cups will have to be replaced andanalysis and a visual inspection of brake components. hydraulic system flushed. (6) Check parking brake operation. Verify freePRELIMINARY BRAKE CHECK movement and full release of cables and foot pedal or (1) If amber antilock light is illuminated, refer to hand lever. Also note if vehicle was being operatedAntilock Brake System Diagnosis. However, if the with parking brake partially applied.red warning light is illuminated, or if no warning (7) If components checked appear OK, proceed tolight is illuminated, continue with diagnosis. Road Test.
ZJ SERVICE BRAKE DIAGNOSIS 5-5ROAD TEST and fluid level. If a problem is confirmed, inspect the (1) If red light is not on, proceed to step (3). wheel brake hydraulic system. (2) If red light is on, proceed as follows: The amber antilock warning light illuminates only (a) See if parking brakes are applied. Release when an ABS circuit fault has occurred. Refer to the them if necessary and proceed to step (b). Antilock Brake Diagnosis section. (b) Note if brake pedal is abnormally low. If pedal is definitely low and red light is on, check PEDAL FALLS AWAY front and rear brake hydraulic circuits for leak. Do A brake pedal that falls away under steady foot not continue with road test. Inspect and re- pressure is generally the result of a system leak. The pair hydraulic components as needed. leak point could be at a brakeline, fitting, hose, or (3) Check brake pedal response with transmission caliper. Internal leakage in the master cylinderin Neutral and engine running. caused by worn or damaged piston cups, may also be (a) If pedal remains firm under steady foot pres- the problem cause. sure, proceed to step (4). If leakage is severe, fluid will be evident at or (b) If pedal falls away, problem is in master cyl- around the leaking component. However internal inder, or HCU on ABS models. Do not road test leakage in the master cylinder may not be physically vehicle; repair as necessary instead. evident. Refer to the cylinder test procedure in this (4) During road test, make normal and firm brake section.stops in 25-40 mph range. Note faulty brake opera-tion such as hard pedal, pull, grab, drag, noise, fade, LOW PEDALpedal pulsation, etc. If a low pedal is experienced and the red light is (5) Inspect brake components after road test and not on, worn lining and rotors are the most likelyrefer to problem diagnosis information for causes of cause.various brake conditions. If the red warning light is on, a system leak has occurred. A leak at a front or rear caliper, brakeline,BRAKE COMPONENT INSPECTION or brake hose will activate the differential pressure Fluid leak points and dragging brake units can switch in the combination valve. The switch willusually be located without removing any components. shuttle forward or rearward depending on where theThe area around a leak point will be wet with fluid. leak is. Switch movement in either direction willThe components at a dragging brake unit (wheel, complete the electrical circuit to the red warningtire, rotor) will be quite warm or hot to the touch. light causing the light to illuminate. Other brake problem conditions will require compo-nent removal for proper inspection. Raise the vehicle SPONGY PEDALand remove the necessary wheels for better visual ac- A spongy pedal is caused by air in the brake hy-cess. draulic system. Brake bleeding will be necessary to During inspection, pay particular attention to purge the air.heavily rusted/corroded brake components (e.g. ro- Air enters the system through leak points and whentors, caliper pistons, cables, brakelines, etc.). the master cylinder reservoir runs dry as a result of a Heavy accumulations of rust may be an indicator of leak. Allowing the cylinder to run dry during brakerust and corrosion damage to a brake component. It bleeding, will also allow air into the system.is wise to remove surface rust in order to accuratelydetermine the depth of rust penetration and damage. HARD PEDAL OR HIGH PEDAL EFFORT Light surface rust is normal and not a major con- A hard pedal or high pedal effort may be due to lin-cern (as long as it is removed, or neutralized). How- ing that is water soaked, contaminated, glazed, or se-ever, heavy rust buildup, especially on high mileage verely worn.vehicles, may actually cover structural damage to The power brake booster, or booster check valvesuch important components as: brakelines, rotors, or could also be faulty. Loss of brake boost will cause abrake booster. hard pedal and high effort. Test the booster and valve as described in this section.SERVICE BRAKE WARNING LIGHT OPERATION The red warning light illuminates when the park- BRAKE DRAGing brakes are applied and when there is a leak in Brake drag occurs when the lining is in constantthe front or rear wheel brake hydraulic circuit. It will contact with the rotor. Drag can occur at one wheel,also illuminate at startup as part of a bulb check. all wheels, fronts only, or rears only. It is a product of If the light comes on, first verify that the parking incomplete brakeshoe release. Drag can be minor orbrakes are fully released. Then check pedal action severe enough to overheat the linings and rotors.
5-6 SERVICE BRAKE DIAGNOSIS ZJ Brake drag also has a direct effect on fuel economy. If stops. If pulsation occurs during light to moderateundetected, minor brake drag can be misdiagnosed as brake stops, a standard brake part is either loose, oran engine or transmission/torque converter problem. worn beyond tolerance. Minor drag will usually cause slight surface char-ring of the lining. It can also generate hard spots in BRAKE PULLrotors from the overheat-cool down process. In most A front pull condition that only occurs when thecases, the rotors, wheels and tires are quite warm to brakes are applied, could result from contaminatedthe touch after the vehicle is stopped. lining in one caliper, seized caliper piston, binding Severe drag can char brakelining all the way caliper, loose caliper, loose or corroded slide pins, im-through. It can also distort and score rotors to the proper brakeshoes, or a damaged rotor.point of replacement. The wheels, tires and brake A worn, damaged wheel bearing or suspension com-components will be extremely hot. In severe cases, ponent are further causes of pull. A damaged frontthe lining may generate smoke as it chars from over- tire (bruised, ply separation) can also cause constantheating. pull that is magnified when the brakes are applied. Common causes of brake drag are: A common and confusing pull condition is where di-• seized or sticking caliper piston rection of pull changes after a few brake stops. The• caliper binding (on bushings, bolts, bracket) cause is a combination of brake drag followed by fade• incorrect length caliper mounting bolts (too long) at the dragging brake unit.• loose or damaged wheel bearing As the dragging brake overheats, efficiency is so re-• loose caliper mounting bracket duced that fade occurs. If the opposite brake unit is• misassembled components still functioning normally, its braking effect is magni-• mispositioned brakelight switch fied. This causes pull to switch direction in favor of• binding brake pedal the brake unit that is functioning normally.• master cylinder internal fault When diagnosing a change in pull condition, re- If brake drag occurs at all wheels, the problem may member that pull will return to the original directionbe related to a blocked master cylinder compensator if the dragging brake unit is allowed to cool downport or faulty power booster (binds-does not release). (and is not seriously damaged).The condition will worsen as system component tem- REAR BRAKE GRABperature increases. Rear grab is usually caused by contaminated lin- An improperly mounted or adjusted brakelight ing, bent or binding shoes, or improperly assembledswitch can prevent full brake pedal return. The re- components.sult will be the same as if the cylinder compensatorports are blocked. In this case, the brakes would be BRAKES DO NOT HOLD AFTER DRIVING THROUGHpartially applied all the time causing drag (which DEEP WATER PUDDLESwill become more severe as component temperature This condition is generally caused by water soakedincreases). lining. If the lining is only wet, it can be dried by driving with the brakes lightly applied for a mile orBRAKE FADE two. However, if the lining is also dirty, shoe removal Brake fade is a product of overheating caused by and cleaning with brake cleaner will be necessary.brake drag. However, brake overheating and subse-quent fade can also be caused by riding the brake CONTAMINATED BRAKELININGpedal, making repeated high deceleration stops in a Brakelining contaminated by water is salvageable.short time span, or constant braking on steep roads. The lining can either be air dried or dried using heat.Refer to the Brake Drag information in this section In cases where brakelining is contaminated by oil,for causes. grease, or brake fluid, the lining should be replaced. Replacement is especially necessary when fluids/lu-PEDAL PULSATION (NON-ABS BRAKES ONLY) bricants have actually soaked into the lining mate- Pedal pulsation is caused by brake parts that are rial. However, grease or dirt that gets onto the liningloose, or out of tolerance limits. This type of pulsa- surface (from handling) during brake repairs, can betion is experienced every time the brakes are applied. cleaned off. Simply spray the lining surface clean Disc brake rotors with excessive lateral runout or with Mopar brake cleaner.thickness variation, or out of round brake drums arethe primary causes of pulsation. BRAKE FLUID CONTAMINATION On vehicles with ABS brakes, remember that pedal There are two basic causes of brake fluid contami-pulsation is normal during antilock mode brake nation. The first involves allowing dirt, debris, or other liquid materials to enter the cylinder reservoir
ZJ SERVICE BRAKE DIAGNOSIS 5-7when the cap or cover is off. The second involves top- Loud brake squeak, squeal, scraping, or grindingping off, or filling the reservoir with non-recom- sounds are a sign of severely worn brake lining. Ifmended fluid. the lining has worn completely through in spots, met- Brake fluid contaminated with only dirt, or debris al-to-metal contact occurs. If the condition is allowedusually retains a normal appearance. Generally, the to continue, rotors can become scored severelyforeign material will remain suspended in the fluid enough to require replacement.and be visible. The fluid and foreign material can beremoved from the reservoir with a suction gun but Thump/Clunkonly if the brakes have not been applied. If the Thumping or clunk noises during braking are fre-brakes are applied after contamination, system flush- quently not caused by brake components. In manying will be required. The master cylinder will also cases, such noises are caused by loose or damagedhave to be flushed or replaced if the contaminants steering, suspension, or engine components. However,cannot be removed. Foreign material lodged in the calipers that bind on the slide surfaces can generatereservoir compensator/return ports can cause brake a thump or clunk noise. In addition, worn out, im-drag by restricting fluid return after brake applica- properly adjusted, or improperly assembled reartion. brakeshoes can also produce a thump noise. Brake fluid contaminated by a non-recommendedfluid, may appear highly discolored, milky, oily look- Chatter/Shuddering, or foamy. In some cases, the fluid may even ap- Brake chatter is usually caused by loose or wornpear to contain sludge. However, be advised that components, or glazed/burnt lining. Rotors with hardbrake fluid will darken in time and occasion- spots can also contribute to chatter. Additional causesally be cloudy in appearance. These are normal of chatter are out-of-tolerance rotors, brake lining notconditions and should not be mistaken for con- securely attached to the shoes, loose wheel bearingstamination. and contaminated brake lining. If some type of oil has been added to the system,the fluid will separate into distinct layers. To verify BRAKELINING CONTAMINATIONthis, drain off a sample with a clean suction gun. Brakelining contamination is a product of leakingThen pour the sample into a glass container and ob- calipers or wheel cylinders, driving through deep wa-serve fluid action. If the fluid separates into distinct ter puddles, or lining that has become covered withlayers, it is definitely contaminated. grease and grit during repair. The only real correction for contamination, is todisassemble and flush the entire hydraulic system WHEEL AND TIRE PROBLEMSand replace all seals. Some conditions attributed to brake components may actually be caused by a wheel or tire problem.BRAKE NOISE A damaged wheel can cause shudder, vibration and pull. A worn or damaged tire can also cause pull.Squeak/Squeal Severely worn tires with little or no tread left can Factory installed brakelining is made from as- produce a grab-like condition as the tire loses and re-bestos free materials. These materials have dif- covers traction.ferent operating characteristics than previous Flat-spotted tires can cause vibration and wheelbrakelining material. Under certain conditions, tramp and generate shudder during brake operation.asbestos free lining may generate some squeak, A tire with internal damage such as a severe bruisegroan or chirp noise. This noise is considered or ply separation can cause pull and vibration.normal and does not indicate a problem. Theonly time inspection is necessary, is when noise PARKING BRAKE DIAGNOSISbecomes constant or when grinding, scrapingnoises occur. Adjustment Mechanism The rear brakeshoes are equipped with wear warn- Parking brake adjustment is controlled by aing tabs. The tabs contact the rotors when the lining cable tensioner. Once the tensioner is adjustedwears to replacement thickness. A constant scraping, at the factory, it should not require further at-squeak type noise will occur at contact. tention. However, there are two instances when Constant brake squeak or squeal may be due to lin- adjustment will be required. The first is when aings that are wet or contaminated with brake fluid, new tensioner, or cables have been installed.grease, or oil. Glazed linings and rotors with hardspots will produce squeak. Dirt and foreign material And the second, is when the tensioner and ca-embedded in the brake lining will also cause squeak/ bles are disconnected for access to other brakesqueal. components.
5-8 SERVICE BRAKE DIAGNOSIS ZJParking Brake Switch And Warning Light Illumination Parking brake adjustment and parts replacement The parking brake switch is in circuit with the red procedures are described in the Parking Brake sec-warning light in the dash. The switch will cause the tion.light to illuminate only when the parking brakes areapplied. If the light remains on after parking brake POWER BRAKE BOOSTER CHECK VALVE TESTrelease, the switch or wires are faulty, or cable ten- (1) Disconnect vacuum hose from check valve.sioner adjustment is incorrect. (2) Remove check valve and valve seal from If the red light comes on while the vehicle is in mo- booster (Fig. 1). Inspect seal for cuts, cracks, tears,tion and brake pedal height decreases, a fault has oc- and replace if necessary.curred in the front or rear brake hydraulic system. (3) Hand operated vacuum pump can be used for test (Fig. 2).Parking Brake problem Causes (4) Apply 15-20 inches vacuum at large end of In most cases, the actual cause of an improperly check valve (Fig. 1).functioning parking brake (too loose/too tight/wont (5) Vacuum should hold steady. If gauge on pumphold), can be traced to a parking brake component. indicates any vacuum loss, valve is faulty and must The leading cause of improper parking brake be replaced.operation, is excessive clearance between theparking brakeshoes and the shoe braking sur-face. Excessive clearance is a result of liningand/or drum wear, drum surface machinedoversize, or inoperative adjuster components. Excessive parking brake lever travel (sometimesdescribed as a loose lever or too loose condition), isthe result of worn brakeshoes, improper brakeshoeadjustment, or improperly assembled brake parts. A ‘‘too loose’’ condition can also be caused by inop-erative or improperly assembled parking brakeshoeparts. A condition where the parking brakes do not hold,will most probably be due to a wheel brake compo-nent. Items to look for when diagnosing a parking brakeproblem, are:• rear brakeshoe wear Fig. 1 Vacuum Check Valve And Seal Location• drum surface (in rear rotor) machined oversize• front cable not secured to lever• rear cable not attached to lever• rear cable seized• parking shoes reversed• parking brake strut not seated in shoes• parking brake lever not seated• parking brake lever bind• cam and lever worn or misassembled• adjuster screws seized• adjuster screws reversed Fig. 2 Typical Hand Operated Vacuum Pump
ZJ SERVICE BRAKE DIAGNOSIS 5-9POWER BRAKE BOOSTER VACUUM TEST (1) Connect a vacuum gauge to the booster checkvalve with a short length of hose and a T-fitting (Fig.3). (2) Start and run engine at idle speed for oneminute. (3) Clamp hose shut between vacuum source andcheck valve (Fig. 3). (4) Stop engine and observe vacuum gauge. (5) If vacuum drops more than one inch HG (33millibars) within 15 seconds, booster diaphragm orcheck valve is faulty. Fig. 3 Booster Vacuum Test Connections
5 - 10 ABS SYSTEM OPERATION ZJ ABS SYSTEM OPERATION INDEX page pageABS Diagnostic Connector . . . . . . . . . . . . . . . . . . 11 Hcu Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 13ABS Operation in Antilock Braking Mode . . . . . . . . 12 Hydraulic Control Unit (HCU) . . . . . . . . . . . . . . . . . 10ABS Operation in Normal Braking Mode . . . . . . . . 12 Ignition Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . 12ABS System Power-Up and Initialization . . . . . . . . 12 System Description . . . . . . . . . . . . . . . . . . . . . . . . 10Acceleration Switch . . . . . . . . . . . . . . . . . . . . . . . . 11 System Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Acceleration Switch Operation . . . . . . . . . . . . . . . . 14 System Warning Light . . . . . . . . . . . . . . . . . . . . . . 12Combination Valve . . . . . . . . . . . . . . . . . . . . . . . . 12 Wheel Speed Sensor Operation . . . . . . . . . . . . . . 13ECU Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Wheel Speed Sensors . . . . . . . . . . . . . . . . . . . . . . 11Electronic Control Unit (ECU) . . . . . . . . . . . . . . . . 11SYSTEM DESCRIPTION • electronic control unit (ECU) The Jeep antilock brake system (ABS) is an elec- • wheel speed sensors and axle shaft tone ringstronically operated, all wheel brake control system. • acceleration switchThe system is designed to prevent wheel lockup and • main relay, pump motor relay,maintain steering control during periods of high • pump motor speed sensorwheel slip when braking. Preventing wheel lockup • ABS warning lightand is accomplished by modulating fluid pressure tothe wheel brake units. HYDRAULIC CONTROL UNIT (HCU) The hydraulic system is a three channel design. The hydraulic control unit (HCU) consists of aThe front wheel brakes are controlled individually valve body, pump body, accumulators, pump motor,and the rear wheel brakes in tandem (Fig. 1). The and wire harnesses (Fig. 2).ABS electrical system is separate from other electri- The pump body, motor, and accumulators are com-cal circuits in the vehicle. A specially programmed bined into an assembly attached to the valve body.electronic control unit (ECU) operates the system The accumulators store the fluid released for ABScomponents. mode operation. The pump provides the fluid volume needed for antilock braking and a DC-type motor runs the pump. The pump/motor is controlled by the ECU. The valve body contains solenoid valves. The sole- noid valves modulate brake pressure during antilock braking. The valves are controlled by the ECU. The HCU provides three channel pressure control to the front and rear brakes. One channel controls the rear wheel brakes in tandem. The two other channels control the front wheel brakes individually. During antilock braking, the solenoid valves are opened and closed as needed. The valves are not static. They are cycled rapidly and continuously to modulate pressure and control wheel slip and decel- eration. At the start of antilock braking, pedal height will decrease as the initial volume of fluid is released to the accumulators. The accumulators then provide the fluid needed for initial operation. The pump motor runs continuously until the ABS mode brake stop is completed. The 1995 master cylinder and HCU are different Fig. 1 Jeep AntiLock System from previous models. The new HCU has built-in ac- cumulators that store the fluid released for antilock ABS system components include: braking. The new master cylinder has a single filler• hydraulic control unit (HCU) cap and the reservoir and HCU are no longer inter-
ZJ ABS SYSTEM OPERATION 5 - 11connected by hoses. The 1995 ABS components arenot interchangeable with prior year ABS compo-nents. Fig. 2 Antilock Hydraulic Control Unit (HCU) Fig. 3 Anti-Lock ECUELECTRONIC CONTROL UNIT (ECU) An electronic control unit (ECU) operates the ABSsystem (Fig. 3). The ECU is separate from other ve-hicle electrical circuits. ECU voltage source isthrough the ignition switch in the Run position. The ECU is located in the engine compartment. Itis mounted on the driver side inner fender panel. The ECU contains dual microprocessors. A logicblock in each microprocessor receives identical sensorsignals which are processed and compared simulta-neously. The ECU contains a self check program that illu-minates the ABS warning light when a system faultis detected. Faults are stored in a diagnostic programmemory and are accessible with the DRB scan tool. ABS faults remain in memory until cleared, or un-til after the vehicle is started approximately 50 Fig. 4 Wheel Speed Sensorstimes. Stored faults are not erased if the battery is ABS DIAGNOSTIC CONNECTORdisconnected. ABS circuit diagnosis is performed with the DRB scan tool. The access point for the scan tool is the di-WHEEL SPEED SENSORS agnostic connector. A speed sensor is used at each wheel. The sensors The connector is under the carpet at the forwardconvert wheel speed into an electrical signal. This end of the console just under the IP center. The con-signal is transmitted to the antilock ECU. nector is black or blue in color and is a 6-way type. A gear type tone ring serves as the trigger mecha-nism for each sensor. The tone rings are mounted atthe outboard ends of the front and rear axle shafts. ACCELERATION SWITCH Different sensors are used at the front and rear An acceleration switch (Fig. 5), provides an addi-wheels (Fig. 4). The front/rear sensors have the same tional vehicle deceleration reference during 4-wheelelectrical values but are not interchangeable. drive operation. The switch is monitored by the an-
5 - 12 ABS SYSTEM OPERATION ZJtilock ECU at all times. The switch reference signal ABS SYSTEM POWER-UP AND INITIALIZATIONis utilized by the ECU when all wheels are deceler- battery voltage is supplied to the ECU ignition ter-ating at the same rate. minal when the ignition switch is turned to Run po- sition. The ECU performs a system initialization procedure at this point. Initialization consists of a static and dynamic self check of system electrical components. The static check occurs immediately after the igni- tion switch is turned in Run position. The dynamic check occurs when vehicle road speed reaches ap- proximately 10 kph (6 mph). During the dynamic check, the ECU briefly cycles the pump to verify op- eration and the HCU solenoids are checked. If an ABS component exhibits a fault during initial- ization, the ECU illuminates the amber warning light and registers a fault code in the microprocessor memory. ABS OPERATION IN NORMAL BRAKING MODE The ECU monitors wheel speed sensor inputs con- tinuously while the vehicle is in motion. However, the ECU will not activate any ABS components as Fig. 5 Acceleration Switch long as sensor inputs and the acceleration switch in- dicate normal braking.SYSTEM RELAYS During normal braking, the master cylinder, power The ABS system has two relays, which are the booster and wheel brake units all function as theymain and motor pump relays. The motor pump relay would in a vehicle without ABS. The HCU pump andis used for the motor pump only. The main relay is solenoids are not activated.used for the solenoid valves. The main relay is con-nected to the ECU at the power control relay termi- ABS OPERATION IN ANTILOCK BRAKING MODEnal. The pump motor relay starts/stops the pump The purpose of the antilock system is to preventmotor when signaled by the ECU. wheel lockup during periods of high wheel slip. Pre- venting lockup helps maintain vehicle braking actionIGNITION SWITCH and steering control. The antilock ECU and warning light are in standby The antilock ECU activates the system whenevermode with the ignition switch in Off or Accessory po- sensor signals indicate periods of high wheel slip.sition. No operating voltage is supplied to the system High wheel slip can be described as the point wherecomponents. wheel rotation begins approaching zero (or lockup) A 12 volt power feed is supplied to the ECU and during braking. Periods of high wheel slip may occurwarning light when the ignition switch is in the Run when brake stops involve high rates of vehicle decel-position. eration. The antilock system prevents lockup during highSYSTEM WARNING LIGHT slip conditions by modulating fluid apply pressure to The amber ABS warning light is in circuit with the the wheel brake units.ECU and operates independently of the red brake Brake fluid apply pressure is modulated accordingwarning light. to wheel speed, degree of slip and rate of decelera- The ABS light indicates antilock system condition. tion. A sensor at each wheel converts wheel speedThe light illuminates for 1-2 seconds at start-up as into electrical signals. These signals are transmittedpart of a bulb check routine. The light goes out when to the ECU for processing and determination ofthe self test program determines system operation is wheel slip and deceleration rate.normal. The ABS system has three fluid pressure control channels. The front brakes are controlled separatelyCOMBINATION VALVE and the rear brakes in tandem (Fig. 1). A speed sen- A combination valve is used with the ABS system. sor input signal indicating high slip conditions acti-The valve contains a front/rear brake pressure differ- vates the ECU antilock program.ential valve and switch and a rear brake proportion- Two solenoid valves are used in each antilock con-ing valve. trol channel. The valves are all located within the
ZJ ABS SYSTEM OPERATION 5 - 13HCU valve body and work in pairs to either increase, Pressure Holdhold, or decrease apply pressure as needed in the in- Both solenoid valves are closed in the pressure holddividual control channels. cycle (Fig. 7). Fluid apply pressure in the control The solenoid valves are not static during antilock channel is maintained at a constant rate. The ECUbraking. They are cycled continuously to modulate maintains the hold cycle until sensor inputs indicatepressure. Solenoid cycle time in antilock mode can be a pressure change is necessary. The pump does notmeasured in milliseconds. run during the pressure hold cycle.HCU OPERATIONNormal Braking During normal braking, the HCU solenoid valves,pump, accumulators, and motor are not activated.The master cylinder and power booster operate thesame as a vehicle without ABS brakes.Antilock Pressure Modulation Solenoid valve pressure modulation occurs in threestages which are: pressure increase, pressure hold,and pressure decrease. The valves are all containedin the valve body portion of the HCU.Pressure Decrease The outlet valve is opened and the inlet valve isclosed during the pressure decrease cycle (Fig. 6). A pressure decrease cycle is initiated when speedsensor signals indicate high wheel slip at one ormore wheels. At this point, the ECU opens the outletvalve, which also opens the return circuit to the ac-cumulators. Fluid pressure is allowed to bleed off (de- Fig. 7 Pressure Hold Cyclecrease) as needed to prevent wheel lock. Pressure Increase Once the period of high wheel slip has ended, the The inlet valve is open and the outlet valve isECU closes the outlet valve and begins a pressure in- closed during the pressure increase cycle (Fig. 8). Thecrease or hold cycle as needed. pressure increase cycle is used to counteract unequal wheel speeds. This cycle controls re-application of fluid apply pressure due to changing road surfaces or wheel speed. WHEEL SPEED SENSOR OPERATION Wheel speed input signals are generated by a sen- sor and tone ring at each wheel. The sensors, which are connected directly to the ECU, are mounted on brackets attached to the front steering knuckles and rear brake support plates. The sensor triggering devices are the tone rings which are similar in appearance to gears. The tone rings are located on the outboard end of each front/ rear axle shaft. The speed sensors generate a signal whenever a tone ring tooth rotates past the sensor pickup face. The wheel speed sensors provide the input signal to the ECU. If input signals indicate ABS mode brak- ing, the ECU causes the HCU solenoids to decrease, hold, or increase fluid apply pressure as needed. The HCU solenoid valves are activated only when wheel speed input signals indicate that a wheel is Fig. 6 Pressure Decrease Cycle approaching a high slip, or lockup condition. At this
5 - 14 ABS SYSTEM OPERATION ZJ these signals for degree of deceleration and wheel slip. If signals indicate normal braking, the solenoid valves are not activated. However, when incoming signals indicate the approach of wheel slip, or lockup, the ECU cycles the solenoid valves as needed. ACCELERATION SWITCH OPERATION The ECU monitors the acceleration switch at all times. The switch assembly contains three mercury switches that monitor vehicle ride height and decel- eration rates (G-force). Sudden, rapid changes in ve- hicle and wheel deceleration rate, triggers the switch sending a signal to the ECU. The switch assembly provides three deceleration rates; two for forward braking and one for rearward braking. ECU OPERATION The antilock ECU controls all phases of antilock operation. It monitors and processes input signals from the system sensors. It is the ECU that activates the solenoid valves to modulate apply pressure during antilock braking. Fig. 8 Pressure Increase Cycle The ECU program is able to determine which wheelpoint, the ECU will cycle the appropriate wheel con- control channel requires modulation and which fluidtrol channel solenoid valves to prevent slip or lockup. pressure modulation cycle to use. The ECU cycles the The wheel sensors provide speed signals whenever solenoid valves through the pressure decrease, holdthe vehicle wheels are rotating. The ECU examines and increase phases.
ZJ BRAKE FLUID—BRAKE BLEEDING—BRAKELINES/HOSES 5 - 15 BRAKE FLUID—BRAKE BLEEDING—BRAKELINES/HOSES INDEX page pageABS Brake Bleeding . . . . . . . . . . . . . . . . . . . . . . . 15 Correct Brake Fluid Level . . . . . . . . . . . . . . . . . . . 15Brakelines and Hoses . . . . . . . . . . . . . . . . . . . . . . 16 Importance of Clean Brake Fluid . . . . . . . . . . . . . . 15Checking Brake Fluid for Contamination . . . . . . . . 15 Recommended Brake Fluid . . . . . . . . . . . . . . . . . . 15RECOMMENDED BRAKE FLUID rial in the fluid, or non-recommended fluids will Recommended brake fluid is Mopar brake fluid, or cause system malfunctions.an equivalent quality fluid meeting SAE J1703 and Clean the reservoir and cap thoroughly beforeDOT 3 standards. checking level or adding fluid. Cap open lines and Brake fluid used in the ABS system must not only hoses during service to prevent dirt entry.meet SAE/DOT standards, it must be exceptionally Dirt or foreign material entering the ABS hydraulicclean as well. Never use substandard fluid, fluid system through the reservoir opening will circulatenot meeting SAE/DOT standards, reclaimed within the system. Dirt or foreign material in thefluid, or fluid from containers that have been system can lead to component malfunction. Alwaysleft open for lengthy periods. clean the reservoir exterior before checking fluid level or adding fluid. Use clean, fresh fluid only toCORRECT BRAKE FLUID LEVEL top off, or refill the system. Correct fluid level is marked on each the side ofthe master cylinder reservoir (Fig. 1). CHECKING BRAKE FLUID FOR CONTAMINATION Preferred fluid level is to the FULL mark. Accept- Oil in the fluid will cause brake system rubberable fluid level is between the ADD and FULL seals to soften and swell. The seals may also becomemarks. porous and begin to deteriorate. If fluid level is below the ADD mark, the brake hy- If fluid contamination is suspected, drain off a sam-draulic system should be checked for leaks. ple from the master cylinder. A suction gun or similarCAUTION: Clean the reservoir cap and exterior thor- device can be used for this purpose.oughly before checking fluid level. Do not allow any Empty the drained fluid into a glass container.dirt or foreign material to enter the reservoir while Contaminants in the fluid will cause the fluid to sep-checking fluid level. Such materials can interfere arate into distinct layers. If contamination has oc-with solenoid valve operation causing an ABS mal- curred, the system rubber seals, hoses and cups mustfunction. be replaced and the system thoroughly flushed with clean brake fluid. ABS BRAKE BLEEDING ABS brake bleeding requires use of the DRB scan tool. The procedure involves performing a conven- tional bleed, followed by use of the scan tool to cycle and bleed the HCU pump and solenoids. A second conventional bleed procedure is then required to en- sure that all air is purged from the system. BRAKE BLEED PROCEDURE (1) If new master cylinder is to be installed, bleed cylinder on bench before installation in vehicle. Refer to procedure in section covering master cylinder ser- vice. (2) Wipe master cylinder reservoir and cap clean. This avoids having dirt or foreign material fall into Fig. 1 Reservoir Fluid Level Indicator Marks reservoir.IMPORTANCE OF CLEAN BRAKE FLUID (3) Fill reservoir with Mopar, or equivalent quality The ABS system brake fluid must be kept clean brake fluid meeting SAE J1703 and DOT 3 stan-and free of any type of contamination. Foreign mate- dards.
5 - 16 BRAKE FLUID—BRAKE BLEEDING—BRAKELINES/HOSES ZJ (4) Perform conventional brake bleed as described (a) Connect scan tool to ABS diagnostic connec-in steps (5) and (6). tor. Connector is under carpet at front of console, (5) Bleed master cylinder and combination valve at just under instrument panel center bezel.brakeline fittings. Have helper operate brake pedal (b) Select CHASSIS SYSTEM, followed bywhile bleeding cylinder and valve. TEVES ABS BRAKES, then BLEED BRAKES. When scan tool displays TEST COMPLETE, dis- connect scan tool and proceed to next step. (8) Repeat conventional bleed procedure described in steps (5) and (6). (9) Top off master cylinder fluid level and verify proper brake operation before moving vehicle. BRAKELINES AND HOSES Metal brakelines and rubber front brake hoses (Figs. 3 and 4), should be inspected periodically and replaced if damaged. The HCU lines with the braided, flexible sections should be replaced if damaged. Do not use substitute brakelines here. Use the flexible braided lines only. Rubber brake hoses should be replaced if cut, cracked, swollen, or leaking. Rubber hoses must only be replaced. They are not repairable parts. The steel brakelines should be checked every time the vehicle is in for normal maintenance. This is im- portant on high mileage vehicles. It is especially im- portant when the vehicle is operated in areas where Fig. 2 Bleed Hose Immersed In Fluid salt is used on road surfaces during winter. (6) Bleed wheel brakes in recommended sequencewhich is: right rear wheel; left rear wheel; right frontwheel; left front wheel. Procedure is as follows: (a) Attach bleed hose to caliper bleed screw. Im- merse end of hose in glass container partially filled with brake fluid. Be sure hose end is submerged in fluid (Fig. 2). (b) Open bleed screw 1/2 turn. Then have helper depress and hold brake pedal. (c) Close bleed screw when brake pedal contacts floorpan. Do not pump brake pedal at any time while bleeding. This compresses air into small bubbles which are distributed throughout system. Additional bleeding will be necessary to remove trapped air. (d) Repeat bleeding operation at each wheel brake unit until fluid entering glass container is free of air bubbles. Check reservoir fluid level fre- quently and add fluid if necessary. (7) Perform HCU bleed procedure with DRB scantool as follows: Fig. 3 Master Cylinder/Combination Valve/HCU Brakeline Connections
ZJ BRAKE FLUID—BRAKE BLEEDING—BRAKELINES/HOSES 5 - 17 Fig. 4 Front Brakeline Routing And Connections Heavily rusted/corroded brakelines should be care- component damage. Severely rusted parts should befully inspected. Heavy rust buildup can hide severe replaced if doubt exists about their condition.
5 - 18 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU INDEX page pageCombination Valve Installation . . . . . . . . . . . . . . . . 20 Master Cylinder Installation . . . . . . . . . ... . . . . . . 23Combination Valve Removal . . . . . . . . . . . . . . . . . 20 Master Cylinder Removal . . . . . . . . . . ... . . . . . . 21General Service Information . . . . . . . . . . . . . . . . . 18 Master Cylinder Reservoir Replacement .. . . . . . . 21HCU Installation . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Power Brake Booster Installation . . . . . ... . . . . . . 27HCU Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Power Brake Booster Operation . . . . . ... . . . . . . 19Master Cylinder Bench Bleeding . . . . . . . . . . . . . . 23 Power Brake Booster Removal . . . . . . ... . . . . . . 27GENERAL SERVICE INFORMATION booster is different as well. The new parts on 1995 A two-piece master cylinder with a 25.4 mm bore models are not interchangeable with prior models.and a 205 mm (8.07 in.) dual diaphragm power brakebooster are used for all applications. Component Service A combination valve is used on all models. The The power brake booster, HCU, and combinationvalve consists of a pressure differential switch and valve are not repairable. These components must bevalve, and a rear proportioning valve. replaced as an assembly whenever diagnosis indi- cates this is necessary.Changes For 1995 The nylon reservoir and grommets are the only ser- A different master cylinder, brake booster, and viceable parts on the master cylinder (Fig. 1). TheHCU are used in 1995 Grand Cherokee models. combination valve bracket is an integral part of the The master cylinder reservoir has a single filler cap valve; it is not removable.and is no longer interconnected with the HCU. The The only serviceable parts on the power brakenew HCU has built-in accumulators to store fluid re- booster (Fig. 1) are the check valve, and vacuumleased for antilock braking. The pedal travel sensor hose. The booster itself is not serviceable. Replacehas been eliminated which means the power brake the booster as an assembly whenever diagnosis indi- cates a malfunction has occurred. Fig. 1 Master Cylinder/Brake Booster Assembly
ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU 5 - 19POWER BRAKE BOOSTER OPERATION How Brake Boost Is Generated Power assist is generated by utilizing the pressureBooster Components differential between normal atmospheric pressure The booster assembly consists of a housing divided and a vacuum. The vacuum needed for booster oper-into separate chambers by two internal diaphragms ation is taken directly from the engine intake mani-(Fig. 2). The outer edge of each diaphragm is at- fold. The entry point for atmospheric pressure istached to the booster housing. The diaphragms are through a filter and inlet valve at the rear of theconnected to the booster primary push rod. housing (Fig. 2). Two push rods are used to operate the booster. The The chamber areas forward of the booster dia-primary push rod connects the booster to the brake phragms are exposed to manifold vacuum. The cham-pedal. The secondary push rod, which connects the ber areas to the rear of the diaphragms, are exposedbooster to the master cylinder, strokes the master to normal atmospheric pressure of 101.3 kilopascalscylinder pistons. (14.7 pounds/square in.). The atmospheric inlet valve is opened and closed Depressing the brake pedal causes the primaryby the primary push rod. The booster vacuum supply push rod to open the atmospheric inlet valve. Thisis through a hose attached to a fitting on the intake action exposes the area behind the diaphragms to at-manifold. The hose is connected to a vacuum check mospheric pressure. The resulting pressure differen-valve in the booster housing. The check valve is a tial is what provides the extra apply pressure forone-way device that prevents vacuum leak back. power assist. Fig. 2 Power Brake Booster Internal Components
5 - 20 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJCOMBINATION VALVE REMOVAL (1) Disconnect clean air and PCV hoses. Then un-snap and remove engine air cleaner top cover (Fig.3). Cover intake manifold inlet with shop towel. Fig. 5 Combination Valve Bracket Attachment (8) Remove combination valve and bracket assem- bly (Fig. 6). Fig. 3 Air Cleaner Top Cover And Hoses (2) Remove brakelines that connect master cylin-der to combination valve (Fig. 4). (3) Disconnect wire from combination valve switchterminal (Fig. 4). Be careful when separating wireconnector as lock tabs are easily damaged if not fullydisengaged. (4) Disconnect brakelines that connect combinationvalve to HCU (Fig. 4). Fig. 6 Combination Valve And Bracket Assembly COMBINATION VALVE INSTALLATION (1) Position valve bracket on booster studs (Fig. 7). (2) Install but do not tighten nuts that secure valve bracket to booster studs. (3) Align and start all four brakeline fittings in combination valve by hand to avoid cross threading. Then tighten fittings just enough to prevent leakage. (4) Tighten combination valve bracket attaching nuts to 25 N⅐m (220 in. lbs.) torque. (5) Connect wire to differential pressure switch in combination valve (Fig. 4). Fig. 4 Combination Valve Connections (6) Tighten brakeline fittings at master cylinder (5) Slide HCU solenoid harness connectors off com- just enough to prevent leakage.bination valve bracket. Then move harness aside for (7) Bleed brakes. Refer to procedure in Brakeworking clearance. Bleeding-Fluid Level-Brakelines section. (6) Remove nuts attaching combination valve (8) Attach HCU solenoid harness connectors tobracket to booster studs (Fig. 5). combination valve bracket. (7) Slide combination valve bracket off booster (9) Install air cleaner top cover and hoses.studs (Fig. 5).
ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU 5 - 21 (8) Remove nuts that attach master cylinder to booster studs. a 6-point deep socket is needed to reach nuts (Fig. 9). Retain nuts as they are spe- cial locking types.Fig. 7 Positioning Valve Bracket On Booster Studs Fig. 9 Master Cylinder Attaching Nut LocationMASTER CYLINDER REMOVAL (9) Remove master cylinder from booster (Fig. 10). (1) Disconnect Loosen clamp that secures clean airhose to intake manifold. Then disconnect PCV hoseat valve. (2) Unsnap air cleaner top cover and remove coverand hoses (Fig. 3). Air filter can either be removed orcovered with shop towel at this time. (3) Cover intake manifold air inlet with shoptowel. (4) Remove windshield washer reservoir attachingscrews. Then lift reservoir upward and position it ontop of fender (Fig. 8). It is not necessary to dis-connect reservoir hoses or wires to positionreservoir on fender. Fig. 10 Master Cylinder Removal MASTER CYLINDER RESERVOIR REPLACEMENT The only serviceable master cylinder parts are the reservoir, grommets, and seal (Fig. 11). The cylinder body is not a repairable item. The body and pistons are only serviced as an assembly. RESERVOIR AND GROMMET REPLACEMENT (1) Remove reservoir cap and empty fluid into drain container. (2) Remove pins that retain reservoir to master cylinder. Use hammer and pin punch to remove pins (Fig. 12).Fig. 8 Windshield Washer Reservoir Positioned On (3) Clamp cylinder body in vise with brass protec- Fender tive jaws. (5) Remove brakelines that connect master cylin- (4) Loosen reservoir from grommets with pry toolder to combination valve (Fig. 4). (Fig. 13). (6) Remove nuts that secure combination valvebracket to booster mounting studs. (7) Slide combination valve bracket off boosterstuds (Fig. 5).
5 - 22 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJ Fig. 14 Reservoir Removal Fig. 11 Master Cylinder And Reservoir Assembly Fig. 15 Grommet Removal (7) Lubricate new grommets with clean brake fluid. (8) Install new grommets in cylinder body (Fig. 16). Use finger pressure only to install and seat grommets. CAUTION: Do not use any type of tool to install the grommets. Tools will cut, or tear the grommets cre- Fig. 12 Removing/Installing Reservoir Retaining Pins ating a leak problem after installation. Install the grommets using finger pressure only. Fig. 13 Loosening Reservoir From Grommets Fig. 16 Grommet Installation (5) Remove reservoir by rocking it to one side andpulling free of grommets (Fig. 14). (9) Start reservoir in grommets. Then rock reser- (6) Remove old grommets from cylinder body (Fig. voir back and forth while pressing downward to seat15). it in grommets.
ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU 5 - 23 (10) Install pins that retain reservoir to cylinder MASTER CYLINDER INSTALLATIONbody (Fig. 12). (1) If new master cylinder is being installed, re- (11) Fill and bleed master cylinder on bench before move protective cover from end of primary piston.installation in vehicle. Then bleed cylinder on bench as described in this section.MASTER CYLINDER BENCH BLEEDING (2) Slide master cylinder onto booster studs. Align A new master cylinder should always be bled be- booster push rod in cylinder primary piston and seatfore installation in the vehicle. This practice saves cylinder against booster.time during brake bleeding because air in the cylin- (3) Install master cylinder attaching nuts (Fig. 18).der will not be pumped into the lines. Tighten nuts to 25 N⅐m (220 in. lbs.) torque. Cylin- The only tools needed for bench bleeding are a vise, der attaching nuts are special locking type. Doa pair of bleed tubes and a wood dowel the same di- not use substitute fasteners.ameter as the cylinder push rod. Bleed tubes can ei-ther be purchased, or fabricated from sparebrakelines and fittings. The bench bleeding procedure is as follows: (1) Mount master cylinder in vise. Clamp vise jawson one of the cylinder mounting ears. (2) Install bleed tubes in cylinder outlet ports anddirect tube ends into appropriate reservoir chambers(Fig. 17). Fig. 18 Master Cylinder Attaching Nut Removal/ Installation (4) Mount combination valve bracket on booster mounting studs. (5) Install brakelines that connect master cylinder to combination valve. Start brakeline fittings by hand to avoid cross threading. (6) Install nuts that attach combination valve bracket to booster mounting studs. Tighten nuts to Fig. 17 Typical Method Of Bench Bleeding Master 25 N⅐m (220 in. lbs.) torque. Cylinder (7) Fill and bleed brake system. (8) Install windshield washer reservoir. (3) Fill reservoir chambers about 3/4 full with (9) Install engine air cleaner top cover and hoses.fresh, clean brake fluid. (4) Bleed cylinder by stroking cylinder pistons in- HCU REMOVALward then allowing them to return under spring (1) Loosen clamp that secures clean air hose to in-pressure. Use a wood dowel, or similar tool to stroke take manifold. Then disconnect PCV hose at valve.pistons (Fig. 17). (2) Unsnap engine air cleaner top cover and re- (5) Continue stroking pistons until bubbles no move cover and hoses (Fig. 19).longer appear in fluid entering reservoir. (3) Remove filter from air cleaner housing (Fig. (6) Remove bleed tubes and install plastic plugs in 19).cylinder outlet ports. Plugs will prevent fluid loss (4) Remove bolts/nuts attaching air cleaner hous-and keep dirt out until cylinder assembly is ready for ing to body panel. Then work housing off ambient airinstallation. duct and remove housing from engine compartment. (7) Top off reservoir fluid level and install cap. (5) Remove windshield washer reservoir attaching screws. Then position on top of fender (Fig. 8). It is not necessary to disconnect reservoir hoses or wires. (6) Slide HCU solenoid harness connector off re- taining tab on combination valve. Then unplug con-
5 - 24 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJ Fig. 21 Combination Valve Assembly Removal (14) Remove three nuts that attach HCU bracket to suspension support panel (Fig. 22). Retain bracket nuts. Fig. 19 Air Cleaner Componentsnector from engine compartment harness and move itaside (Fig. 20). Fig. 20 HCU Solenoid Harness Connector Fig. 22 Removing HCU Bracket Attaching Nuts (7) Disconnect wire from combination valve switch (15) Disconnect HCU pump motor harness (Fig. 23).(Fig. 4). Be careful when separating wire connectoras lock tabs are easily damaged if not fully disen-gaged. (8) Remove brakelines that connect master cylin-der to combination valve (Fig. 4). (9) Disconnect remaining two brakelines (fromHCU) at combination valve. (10) Remove nuts attaching combination valvebracket to booster mounting studs. (11) Slide combination valve bracket off boostermounting studs and remove valve (Fig. 21). Ifbracket is tight fit, use pry tool to work bracket offstuds. (12) Remove nuts attaching master cylinder tobooster mounting studs (Fig. 22). Retain cylinderattaching nuts as they have a special interfer-ence fit thread. Fig. 23 HCU Pump Motor Harness Connector (13) Remove master cylinder (Fig. 10).
ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU 5 - 25 (16) Disconnect three brakelines at rear of HCU (21) Inspect rubber isolators and sleeves in HCU(Fig. 24). These are lines that connect HCU to front/ bracket (Figs. 26 and 27). Replace any washers orrear brakes. isolators if missing, or damaged with factory replace- ment parts only. Do not use substitute fasteners. Fig. 26 HCU Bracket Bolt Location Fig. 24 Brakeline Connections (17) If HCU is to be replaced, remove flex linesfrom HCU. These are lines that connect HCU to com-bination valve. (18) Lift HCU and bracket off mounting studs andremove assembly from engine compartment (Fig. 25). (19) If HCU is to be replaced, remove three bolts Fig. 27 HCU Bracket Isolators and Sleeves HCU INSTALLATION (1) If new HCU is being installed, transfer mount- ing bracket to new HCU. Be sure to use original shoulder style bolts to attach bracket to HCU; do not use substitute fasteners. (2) If stud plate that attaches HCU bracket to sus- pension support panel, was removed, position stud plate on underside of panel and secure it with new retaining nuts (Fig. 29). (3) Position HCU bracket on mounting studs (Fig. 30). Then install and tighten bracket attaching nuts to 10-13 N⅐m (92-112 in. lbs.) torque. (4) Align and start brakeline fittings into ports at rear of HCU (Fig. 31). Start fittings by hand to Fig. 25 HCU And Bracket Removal avoid cross threading. Then tighten fittings to 14-16 N⅐m (125-140 in. lbs.) torque.attaching mounting bracket to HCU (Fig. 26). (5) Slide master cylinder onto booster studs (Fig. (20) Separate bracket from HCU (Fig. 27). Note 32). Align booster push rod in cylinder primary pis-that special shoulder bolts are used to attach ton and seat cylinder against booster.bracket to HCU. If bolts are damaged, do not (6) Install and tighten master cylinder attachinguse substitute bolts. Use factory replacement nuts to 25 N⅐m (220 in. lbs.) torque. Cylinder at-bolts only.
5 - 26 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJ Fig. 31 HCU Brakeline Installation (To Front/Rear Brakes) Fig. 29 Stud Plate And HCU Bracket Attachment Fig. 32 Master Cylinder/Combination Valve Installation (13) Fill and bleed brake system. Bleed procedure is described in section covering Brake Bleeding-Fluid Level-Brakelines. Tighten brakelines at HCU, master Fig. 30 HCU Installation cylinder and combination to specified torque (Fig.taching nuts are special and have an interfer- 33).ence fit thread. Do not use substitute fasteners (14) Install windshield washer reservoir.at any time. (15) Install air cleaner housing, filter, top cover, (7) Install combination valve (Fig. 32). Be sure and hoses.valve bracket is seated on booster mounting studs. (8) Connect brakelines from HCU to combination POWER BRAKE BOOSTER REMOVALvalve. Start brakeline fittings by hand to avoid cross (1) Disconnect battery negative cable.threading. (2) Remove air cleaner top cover, filter, housing, (9) Install master cylinder-to-combination valve and hoses.brakelines. Start brakeline fittings by hand to (3) Remove screws attaching windshield washeravoid cross threading. reservoir to fender panel. Then position reservoir on (10) Install nuts that attach combination valve top of fender.bracket to booster mounting studs. Tighten nuts to (4) Remove master cylinder, combination valve,25 N⅐m (220 in. lbs.) torque. and HCU. Refer to procedures in this section. (11) Connect HCU solenoid and pump motor wire (5) Disconnect vacuum hose at booster check valveharnesses. (Fig. 34). (12) Connect wire to combination valve switch. (6) Inside passenger compartment:
ZJ MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU 5 - 27 Fig. 33 Brakeline Connections (At Master Cylinder/Combination Valve/HCU) Fig. 34 Booster Check Valve And Hose (a) Remove retainer clip that booster push rod to pedal pin (Fig. 35). Then slide push rod off pin. (b) Remove four locknuts that attach booster to dash panel (Fig. 35). (7) In engine compartment, slide booster forward, Fig. 35 Power Brake Booster Mountingtilt it upward slightly, and remove it from enginecompartment. POWER BRAKE BOOSTER INSTALLATION (8) If booster will be stored on bench for any length (1) Check condition of grommet that secures checkof time, cover booster with shop towels to prevent valve in booster. Replace grommet if cut, torn, ordust entry and place short lengths of rubber hose loose (no longer secures valve tightly).over booster studs to protect threads.
5 - 28 MASTER CYLINDER—BRAKE BOOSTER—COMBINATION VALVE—HCU ZJ (2) Wipe booster mounting surface of dash panel (9) Install windshield washer reservoir.clean with shop towel. (3) Align and position booster on engine compart-ment side of dash panel. (4) Inside passenger compartment: (a) Lubricate pedal pin and bushing with Mopar multi-mileage grease. (b) Install booster attaching nuts on studs. Tighten attaching nuts to 41 N⅐m (30 ft. lbs.) torque. (c) Slide booster push rod on pedal pin. Then se- cure rod to pin with retainer clip. (5) In engine compartment, attach vacuum hose tobooster check valve (Figs. 36 and 37). (6) Install master cylinder, combination valve, andHCU. Refer to procedures in this section. (7) Bleed brakes. Refer to section covering brakebleeding. Fig. 36 Vacuum Hose Connection (5.2L) (8) Install engine air cleaner and hoses. Fig. 37 Vacuum Hose Connection (4.0L)
ZJ SPEED SENSORS—TONE WHEELS—ACCELERATION SWITCH—ECU 5 - 29 SPEED SENSORS—TONE WHEELS—ACCELERATION SWITCH—ECU INDEX page pageAcceleration Switch Installation . . . . . . . . . . . . . . . 31 Rear Wheel Sensor Installation and Adjustment . . . 30Acceleration Switch Removal . . . . . . . . . . . . . . . . 31 Rear Wheel Sensor Removal ............. . . . 30ECU Installation . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Service Information . . . . . . . . ............. . . . 29ECU Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Speed Sensor Air Gap . . . . . ............. . . . 29Front Wheel Sensor Installation . . . . . . . . . . . . . . . 29 Tone Wheel Service . . . . . . . ............. . . . 29Front Wheel Sensor Removal . . . . . . . . . . . . . . . . 29SERVICE INFORMATION The ECU, speed sensors, and acceleration switchused in the antilock brake system are not repairableparts. They are serviced as assemblies only.TONE WHEEL SERVICE The axle shaft tone wheels are not serviceable. If atone wheel becomes damaged, it will be necessary toreplace the axle shaft.SPEED SENSOR AIR GAP Front sensor air gap is fixed and not adjustable.Only rear sensor air gap is adjustable. Although front sensor air gap is not adjustable, itcan be checked if diagnosis indicates this is neces-sary. Front air gap should be 0.40 to 1.3 mm (0.0157 Fig. 1 Front Wheel Sensor Locationto 0.051 in.). If gap is incorrect, the sensor is eitherloose, or damaged. Rear sensor air gap adjustment is only neededwhen reinstalling an original sensor. Replacementsensors have an air gap spacer attached to the sensorpickup face. The spacer establishes correct air gapwhen pressed against the tone ring during installa-tion. As the tone ring rotates, it peels the spacer offthe sensor to create the required air gap. Rear sensorair gap is 0.92-1.45 mm (0.036-0.057 in.). Sensor air gap measurement, or adjustment proce-dures are provided in this section. Refer to the front,or rear sensor removal and installation procedures asrequired.FRONT WHEEL SENSOR REMOVAL (1) Turn ignition switch to OFF position. (2) Raise vehicle. Fig. 2 Front Wheel Sensor Wire Routing (3) Remove wheel and tire. FRONT WHEEL SENSOR INSTALLATION (4) Remove bolt attaching front sensor to steering (1) Apply Mopar Lock N’ Seal or Loctite 242 toknuckle (Fig. 1). sensor attaching bolt. Use new sensor bolt if original (5) Disengage sensor wire from brackets on steer- bolt is worn or damaged.ing knuckle and frame member (Figs. 2 and 3). (2) Position sensor on steering knuckle. Seat sen- (6) Unseat grommet that secures sensor wire in sor locating tab in hole in knuckle and install sensorfender panel (Fig. 3) (7) In engine compartment, disconnect sensor wire attaching bolt finger tight.connector at harness plug (Fig. 4). (3) Tighten sensor bolt to 14 N⅐m (11 ft. lbs.) (8) Remove sensor and wire assembly. torque.
5 - 30 SPEED SENSORS—TONE WHEELS—ACCELERATION SWITCH—ECU ZJ (2) Disconnect rear sensor wires at harness connec- tors. (3) Push sensor wires and grommets through floor- pan holes. (4) Raise vehicle. (5) Remove wheel and brake drum. (6) Disengage sensor wire from axle and chassis brackets and from brakeline retainers (Fig. 5). (7) Unseat sensor grommet from brake support plate. (8) Remove bolt attaching sensor to support plate bracket (Fig. 6). (9) Remove sensor and wire through opening in support plate.Fig. 3 Front Wheel Sensor Wire Grommet Location (4) Route sensor wire from steering knuckle tofender panel. (5) Engage grommets on sensor wire in brackets onbody, chassis, frame, and steering knuckle. (6) Check sensor wire routing. Be sure wire isclear of all chassis components and is not twisted orkinked at any spot. (7) Seat sensor wire in body grommet and seatgrommet in fender panel (Fig. 4). (8) Connect sensor wire to harness in engine com- Fig. 5 Rear Wheel Sensor Wire Attachmentpartment. Fig. 6 Rear Wheel Sensor Mounting REAR WHEEL SENSOR INSTALLATION AND ADJUSTMENT (1) Insert sensor wire through support plate hole. Then seat sensor wire grommet in hole to secure wire. (2) Apply Mopar Lock N’ Seal or Loctite 242 to original sensor bolt. Use new bolt if original is worn or damaged. (3) Install sensor bolt finger tight only at this time. (4) Set sensor air gap as follows: Fig. 4 Front Sensor Wire Routing (Left Front Shown) (a) If original sensor is being installed or ad- justed, remove any remaining pieces of cardboardREAR WHEEL SENSOR REMOVAL spacer from sensor pickup face. Set air gap to 0.92- (1) Raise and fold rear seat forward. Then move 1.45 mm (0.036-0.057 in.) with feeler gauge (Fig.carpeting aside for access to rear sensor connectors. 7). Tighten sensor bolt to 14 N⅐m (11 ft. lbs.) torque.
ZJ SPEED SENSORS—TONE WHEELS—ACCELERATION SWITCH—ECU 5 - 31 (b) If new sensor is being installed, push card- board spacer on sensor face (Fig. 8) against tone ring. Then tighten sensor bolt to 14 N⅐m (11 ft. lbs.) torque. Correct air gap will be established as tone ring rotates and peels spacer off sensor face. Fig. 8 New Rear Sensor With Air Gap Spacer Fig. 7 Setting Air Gap On Original Rear Sensor (3) Tilt rear seat assembly forward for access to (5) Route sensor wires to rear seat area. sensor. (6) Feed sensor wires through floorpan access hole (4) Disconnect sensor harness (Fig. 9).and seat sensor grommets in floorpan. (5) Remove screws attaching sensor to bracket. (7) Secure sensor wire in brackets and in retainers (6) Remove sensor.on rear brakelines. Verify that sensor wire is secureand clear of rotating components. ACCELERATION SWITCH INSTALLATION (8) Install brake drum and wheel and lower vehi- (1) Note position of locating arrow on switch. Posi-cle. tion switch so arrow faces forward. (9) Fold rear seat and carpet forward for access tosensor wires and connectors. CAUTION: The mercury switch (inside the accelera- (10) Connect sensor wires to harness connectors. tion switch), will not function properly if the switch (11) Reposition carpet and fold rear seat down. is mispositioned. Verify that the locating arrow is pointing to the front of the vehicle.ACCELERATION SWITCH REMOVAL (1) Turn ignition switch to OFF position. (2) Position switch in mounting bracket (Fig. 9). (2) Disconnect battery negative cable. Fig. 9 Acceleration Sensor Mounting
5 - 32 SPEED SENSORS—TONE WHEELS—ACCELERATION SWITCH—ECU ZJ (3) Install and tighten switch attaching screws to (7) Lift ECU off driver side inner fender panel and2-4 N⅐m (17-32 in. lbs.) torque. out of engine compartment (Fig. 12). (4) Connect harness to switch. Be sure harnessconnector is firmly seated. (5) Move rear seat back to normal position. (6) Connect battery negative cable.ECU REMOVAL (1) Turn ignition switch to OFF position. (2) Remove engine air cleaner and hoses. (3) On California 4.0L models, disconnect and re-move duty purge solenoid and bracket (Fig. 10). So-lenoid and bracket must be removed for access toECU bracket. Fig. 12 ECU And Bracket Removal (8) If ECU will be replaced, remove mounting bracket from ECU. ECU INSTALLATION (1) If new ECU is being installed, transfer mount- ing bracket to new ECU (Fig. 13).Fig. 10 Duty Purge Solenoid And Bracket Mounting (4) Release strap securing harness connector toECU pin terminals (Fig. 11). Use tool such as smallflat blade screwdriver to lift metal strap upward torelease it. (5) Disconnect harness connector from ECU. Tiltconnector upward to disengage it from ECU pin ter-minals. Then slide it out of retaining tangs in ECU. Fig. 13 Mounting Bracket Position On ECU (2) Position ECU on fender panel and install at- taching screws/nuts. (3) On California 4.0L models, install duty purge solenoid and bracket on fender panel (Fig. 10). Then connect harness to solenoid. (4) Align and attach harness connector to ECU. Slide connector into engagement with tangs on ECU. Fig. 11 Releasing ECU Harness Connector Strap Then tilt connector downward and into engagement with ECU pin terminals. Exercise care as pin termi- (6) Remove screws/nuts attaching ECU bracket to nals can be damaged if connector is forced into place.fender panel. (5) Install engine air cleaner and hoses.
ZJ FRONT DISC BRAKES 5 - 33 FRONT DISC BRAKES INDEX page pageCaliper Operation and Wear Compensation . . . . . . 33 Front Caliper Removal . . . . . . . . . . . . . . . . . . . . . 36Front Brakeshoe Installation . . . . . . . . . . . . . . . . . 35 Front Rotor Installation . . . . . . . . . . . . . . . . . . . . . 40Front Brakeshoe Removal . . . . . . . . . . . . . . . . . . . 34 Front Rotor Removal . .. . . . . . . . . . . . . . . . . . . . . 39Front Caliper Assembly . . . . . . . . . . . . . . . . . . . . . 38 General Information . .. . . . . . . . . . . . . . . . . . . . . 33Front Caliper Disassembly and Overhaul . . . . . . . . 37 Wheel Nut Tightening .. . . . . . . . . . . . . . . . . . . . . 40Front Caliper Installation . . . . . . . . . . . . . . . . . . . . 39GENERAL INFORMATION Grand Cherokee models are equipped with singlepiston, floating-type front disc brake calipers. Venti-lated rotors are used at the front and solid rotors areused at the rear. The front calipers are supported in mounting armsthat are an integral part of the steering knuckle. Thecalipers slide on mounting bolts that also attach thecalipers to the steering knuckle.CALIPER OPERATION AND WEAR COMPENSATIONCaliper Operation The significant feature of single piston caliper op-eration is that the calipers are free to slide laterallyon the mounting bolts. It is the freedom of lateralmovement that allows continuous compensation forlining wear. A simplified cross section of a single piston caliperis shown in Figure 1. The illustration portrays theforces at work when the brakes are applied. At brake application, fluid pressure exerted againstthe caliper piston increases greatly. Of equal impor-tance, is the fact that fluid pressure is exerted Fig. 1 Disc Brake Caliper Operationequally and in all directions. This means pressure ex- piston. Upon release of the pedal, the caliper and pis-erted against the caliper piston and within the cali- ton return to a rest position. The brakeshoes do notper bore will be equal. retract an appreciable distance from the rotor. In Fluid pressure applied to the piston is transmitted fact, clearance is usually at, or close to zero. The rea-directly to the inboard brakeshoe. This forces the sons for this are to keep road debris from getting be-shoe lining against the inner surface of the disc tween the rotor and lining and in wiping the rotorbrake rotor (Fig. 1). At the same time, fluid pressure surface clear each revolution.within the piston bore forces the caliper to slide in- The caliper piston seal controls the amount of pis-ward on the mounting bolts. This action brings the ton extension needed to compensate for normal liningoutboard brakeshoe lining into contact with the outer wear.surface of the disc brake rotor (Fig. 1). During brake application, the seal is deflected out- In summary, fluid pressure acting simultaneously ward by fluid pressure and piston movement (Fig. 2).on both piston and caliper, produces a strong clamp- When the brakes (and fluid pressure) are released,ing action. When sufficient force is applied, friction the seal relaxes and retracts the piston.will stop the rotors from turning and bring the vehi- The amount of piston retraction is determined bycle to a stop. brakelining wear. Generally, the amount is just enough to maintain contact between the piston andBrakeshoe Wear Compensation inboard brakeshoe. Brakelining running clearance at Application and release of the brake pedal gener- the rotor, will be held between zero and a maximumates only a very slight movement of the caliper and of 0.12 mm (0.005 in.).
5 - 34 FRONT DISC BRAKES ZJ Fig. 2 Lining Wear Compensation By Piston SealFRONT BRAKESHOE REMOVAL (1) Raise vehicle and remove front wheels. (2) If brakeshoes are severely worn, drain smallamount of fluid from master cylinder front brake res- Fig. 4 Caliper Mounting Bolt Removal/Installationervoir with suction gun. (3) Bottom caliper piston in caliper bore withC-clamp. Position clamp screw on outboard brake-shoe and frame of clamp on rear of caliper. Do notallow clamp screw to bear directly on outboardshoe retainer spring. Use wood or metal spacerbetween shoe and clamp screw if necessary. Atypical method of bottoming piston with C-clamp isshown in Figure 3. Fig. 5 Tilting Caliper Outward until retainer spring clears caliper. Then press oppo- site end of shoe inward to disengage opposite shoe lug and rotate shoe up and out of caliper (Fig. 7). Fig. 3 Bottoming Caliper Piston With C-Clamp (4) Remove caliper mounting bolts (Fig. 4). Ifbrakeshoes are being removed to correct a pullor drag condition, verify length of caliper boltsas they may be incorrect length. Refer to boltinformation in brakeshoe installation proce-dure. (5) Tilt top of caliper outward. Use pry tool if nec-essary (Fig. 5). (6) Lift caliper off steering knuckle (Fig. 6). (7) If original brakeshoes will be used, keepthem in sets (left and right as they are not in- Fig. 6 Front Caliper Removalterchangeable. (8) Remove outboard shoe. Press one end of shoeinward to disengage shoe lug and rotate shoe upward
ZJ FRONT DISC BRAKES 5 - 35 Fig. 7 Outboard Brakeshoe Removal Fig. 9 Front Caliper Dust Boot And Bushing (9) Remove inboard shoe. Grasp ends of shoe and Locationstilt shoe outward to release springs from caliper pis-ton (Fig. 8). Then remove shoe from caliper. (3) Install inboard shoe in caliper (Fig. 10). Be sure shoe retaining springs are fully seated in caliper pis- ton. (4) Install outboard shoe in caliper (Fig. 11). Start one end of shoe in caliper and rotate shoe downward and into place until shoe locating lugs and shoe spring are seated in caliper. Fig. 8 Front Inboard Brakeshoe Removal (10) Support caliper on box, mechanics stool, orsimilar device. Do not allow brake hose to sup-port caliper weight. (11) Wipe caliper off with shop rags or towels. Donot use compressed air. Compressed air can un- Fig. 10 Front Inboard Disc Brakeshoe Installationseat dust boot and force dirt into piston bore. (12) Inspect condition of caliper piston dust boot (5) Verify that locating lugs on outboard shoe are(Fig. 9). Overhaul caliper if there is evidence of leak- seated in caliper (Fig. 6).age past piston and dust boot. Then inspect caliper (6) Install caliper. Position notches at lower end ofbushings and boots (Fig. 9). Replace boots if torn or brakeshoes on bottom mounting ledge of steeringcut. If bushings or boots are damaged, replace them. knuckle. Then rotate caliper onto rotor and seat tabs at upper ends of brakeshoes on top mounting ledgeFRONT BRAKESHOE INSTALLATION (Fig. 12). (1) Lubricate caliper mounting bolts and bushings (7) Check brakeshoe position on steering knuckle(Fig. 9) with GE 661 or Dow 111 silicone grease. mounting ledges. Be sure notches at lower end of (2) Keep new or original brakeshoes in sets. brakeshoes are securely seated on bottom mountingThey should never be interchanged from side to ledges. Then verify that tabs at upper ends of shoesside. are seated on top mounting ledge (Fig. 12).
5 - 36 FRONT DISC BRAKES ZJFig. 11 Front Outboard Disc Brakeshoe Installation Fig. 13 Correct Front Brake Hose Routing (Driver Side Shown) Fig. 12 Front Caliper And Brakeshoe InstallationCAUTION: Before securing the caliper, be sure the Fig. 14 Caliper Mounting Bolt Dimensionsfront brake hose is not twisted, kinked or touching (10) Turn ignition On and run pump until it shutsany chassis components (Fig. 13). off. Then pump brake pedal until shoes are seated. (8) Lubricate and install caliper mounting bolts. (11) Top off brake fluid level if necessary. Use Mo-Start bolts by hand then tighten bolts to 10-20 N⅐m par brake fluid or equivalent meeting SAE J1703 and(7-15 ft. lbs.) torque. DOT 3 standards only.CAUTION: If new caliper bolts are being installed, FRONT CALIPER REMOVALor if the original reason for repair was a drag/pull (1) Raise vehicle and remove front wheels.condition, check caliper bolt length before proceed- (2) If brakeshoes are severely worn, drain smalling. If the bolts have a shank length greater than amount of fluid from master cylinder front brake res-67.6 mm (2.66 in.), they will contact the inboard ervoir with suction gun.brakeshoe causing a partial apply condition. Refer (3) Bottom caliper piston in caliper bore withto Figure 14 for required caliper bolt length. C-clamp. Position clamp screw on outboard brake- shoe and frame of clamp on rear of caliper. Do not (9) Install wheels. Tighten wheel nuts to 109-150 allow clamp screw to bear directly on outboardN⅐m (80-110 ft. lbs.) torque. shoe retainer spring. Use wood or metal spacer
ZJ FRONT DISC BRAKES 5 - 37between shoe and clamp screw if necessary. Atypical method of bottoming piston with C-clamp isshown in Figure 3. (4) Remove caliper mounting bolts (Fig. 4). (5) Tilt top of caliper outward. Use pry tool if nec-essary (Fig. 5). (6) Lift caliper off steering knuckle (Fig. 6). (7) If original brakeshoes will be used, keepthem in sets left and right, as they should notbe interchanged. (8) Remove front brake hose fitting bolt and wash-ers. Then remove caliper from vehicle. (9) Cover open end of front brake hose to preventdirt entry. Use tape or shop towels.FRONT CALIPER DISASSEMBLY AND OVERHAUL (1) Remove outboard and inboard brakeshoes fromcaliper. (2) Pad interior of caliper with minimum, one-inchthickness of shop towels (Fig. 15). Towels are neededto protect caliper piston during removal. Fig. 16 Caliper Piston Removal Fig. 15 Padding Caliper Interior To Protect Piston During Removal (3) Remove caliper piston with short bursts of lowpressure compressed air. Direct air through fluid in- Fig. 17 Removing Caliper Piston Dust Bootlet port and ease piston out of bore (Fig. 16). FRONT CALIPER CLEANING AND INSPECTION Clean the caliper and piston with clean brake fluidCAUTION: Do not blow the piston out of the bore or Mopar brake cleaning solvent only. Do not use gas-with sustained air pressure. This could result in acracked piston. Use only enough air pressure to oline, kerosene, paint thinner, or similar types as aease the piston out. In addition, NEVER attempt to solvent. These products may leave a residue thatcatch the piston as it leaves the bore. This could re- could damage the piston and seal.sult in personal injury. Wipe the caliper and piston dry with lint free tow- els or use low pressure compressed air. (4) Remove caliper piston dust boot. Either pry Inspect the piston and piston bore. Replace the cal-boot out of caliper with suitable tool, or collapse boot iper if the bore is corroded, rusted, or scored. Do notwith punch to remove it (Fig. 17). hone the caliper piston bore. Replace the caliper if (5) Remove and discard caliper piston seal with the bore is damaged.pencil, or plastic tool (Fig. 18). Do not use metal tools Inspect the caliper piston. The piston is made fromas they will scratch piston bore. a phenolic resin and should be smooth and clean. (6) Remove caliper mounting bolt bushings and Surface discoloration is normal but replace the pistonboots (Fig. 19).
5 - 38 FRONT DISC BRAKES ZJ (2) Install new piston seal in caliper bore. Press seal into seal groove with finger (Fig. 20). Fig. 18 Removing Caliper Piston Seal Fig. 20 Installing Caliper Piston Seal (3) Install dust boot on caliper piston (Fig. 21). Fig. 19 Caliper Bushing And Boot Removalif cracked, chipped, or scored. Do not attempt to re-store a scored piston surface by sanding or polishing.CAUTION: Never interchange phenolic resin and Fig. 21 Installing Dust Boot On Caliper Pistonsteel caliper pistons. The seals, seal grooves, cali- (4) Start caliper piston in bore and into seal byper bores and piston tolerances are different for hand (Fig. 22). Use a twisting, rocking motion toresin and steel pistons. Do not intermix these com- start piston into seal. Keep piston level during instal-ponents. lation to avoid cocking seal. (5) Once piston is started in seal, press piston Inspect the caliper bushings and boots. Replace the about 2/3 of way into bore. A large C-clamp orboots if cut or torn. Clean and lubricate the bushings bench vise can be used to press piston into bore. Bewith GE 661 or Dow 111 silicone grease if necessary. sure to place a wood block between piston and Inspect condition of the caliper mounting bolts. Re- vise jaws or C-clamp. Piston is made of phe-place the bolts if corroded, rusted, or worn. Do not nolic resin and can be cracked if care is not ex-reuse the bolts if unsure of their condition. ercised. Length of the caliper mounting bolts is also ex- (6) Seat dust boot in caliper with Special Tooltremely important. Use the replacement bolts C-4842 (Fig. 23).specified in the parts catalog at all times. Do (7) Install caliper bleed screw if removed.not use substitute bolts. Bolts that are too long (8) Lubricate caliper mounting bolt bushings andwill partially apply the inboard brakeshoe interior of bushing boots with GE 661 or Dow 111 sil-causing drag and pull. Refer to the caliper and icone grease.brakeshoe installation procedures for service details (9) Install rubber bushing boots in caliper (Fig.and bolt dimensions. 24). Fold boots in half and work them into caliper. Be sure boots are centered in caliper.FRONT CALIPER ASSEMBLY (10) Install bushings in boots. Be sure boot is (1) Coat caliper piston bore, new piston seal and seated in groove at each end of bushing (Fig. 24).piston with liberal quantity of clean, fresh brake (11) Install brakeshoes in caliper (Figs. 7, 8).fluid. (12) Install caliper bleed screw if removed.
ZJ FRONT DISC BRAKES 5 - 39 Fig. 24 Installing Bushings And Boots Fig. 22 Caliper Piston Installation Fig. 25 Front Brake Hose And Fitting Components 67.6 mm (2.66 in.), they may contact the inboard brakeshoe causing a partial apply condition. Refer to Figure 14 for the required caliper bolt length. (4) Position front brake hose clear of all chassis components and tighten caliper fitting bolt to 24-38 Fig. 23 Seating Dust Boot In Caliper N⅐m (216-336 in. lbs.) torque.FRONT CALIPER INSTALLATION (1) Connect brake hose fitting to caliper but do not CAUTION: Be sure the front brake hose is nottighten fitting bolt completely at this time. Install twisted or kinked at any point. Also be sure thenew washers on fitting bolt to avoid leaks (Fig. hose is clear of all steering and suspension compo-25). nents. Loosen and reposition the hose if necessary. (2) Install caliper over rotor and into mounting (5) Install wheel and tire assemblies. Tightenbracket. Position notches at each end of brakeshoes wheel nuts to 109-150 N⅐m (80-110 ft. lbs.) torque.on mounting bracket ledges. (6) Bleed brake system. (3) Coat caliper mounting bolts with GE 661 orDow 111 silicone grease. Then install and tighten FRONT ROTOR REMOVALbolts to 10-20 N⅐m (7-15 ft. lbs.) torque. (1) Raise vehicle and remove wheel. (2) Remove caliper.CAUTION: If new caliper bolts are being installed, (3) Remove push nuts securing rotor to hub studsor if the original reason for repair was a drag/pull (Fig. 26).condition, check caliper bolt length before proceed- (4) Remove rotor from hub (Fig. 27).ing. If the bolts have a shank length greater than
5 - 40 FRONT DISC BRAKES ZJ (5) If rotor shield requires service, remove front FRONT ROTOR INSTALLATIONhub and bearing assembly. (1) Install rotor on hub (Fig. 27). (2) Install caliper. (3) Install wheel and lower vehicle. WHEEL NUT TIGHTENING The wheel attaching nuts must be tightened prop- erly to ensure efficient brake operation. Overtighten- ing the nuts or tightening them in the wrong sequence can cause distortion of the brake rotors and drums. Impact wrenches are not really recommended for tightening wheel nuts. A torque wrench is preferred Fig. 26 Front Rotor Push Nut Location for this purpose. Correct tightening torque is 109-150 N⅐m (80-110 ft. lbs.). The correct tightening sequence is important in avoiding rotor and drum distortion. The correct se- quence is in a diagonal crossing or star pattern. Seat the wheel and install the wheel nuts finger tight. Tighten the nuts in sequence to half the required torque. Then repeat the tightening sequence to final specified torque. Fig. 27 Front Rotor Removal/Installation
ZJ REAR DISC BRAKES 5 - 41 REAR DISC BRAKES INDEX page pageGeneral Information . . . . . . . . . . . . . . .. . . . . . . . 41 Rear Caliper Operation and Wear Compensation . . 41Rear Brakeshoe Installation . . . . . . . . . .. . . . . . . . 42 Rear Caliper Removal . . . . . . . . . . . . . . . . . . . . . . 43Rear Brakeshoe Removal . . . . . . . . . . .. . . . . . . . 41 Rear Rotor Installation . . . . . . . . . . . . . . . . . . . . . 47Rear Caliper Assembly . . . . . . . . . . . . .. . . . . . . . 44 Rear Rotor Removal . . . . . . . . . . . . . . . . . . . . . . . 46Rear Caliper Disassembly and Overhaul . . . . . . . . 43 Wheel Nut Tightening . . . . . . . . . . . . . . . . . . . . . . 47Rear Caliper Installation . . . . . . . . . . . .. . . . . . . . 46GENERAL INFORMATION iper bracket shoe contact surfaces are machined for Rear disc brake components consist of single piston, the new shoes. There are dimensional differences be-floating-type, rear disc brake calipers and solid rotors. tween the 1995 and prior built calipers, shoes, and The rear calipers are mounted in a bracket at- brackets. It is important that these parts not be in-tached to the rear axle tube flange (Fig. 1). The cal- terchanged at any time.ipers are secured to the bracket with mounting bolts.The bracket also secures the rear disc brake rotorsplash shield to the tube flange. Fig. 2 Rear Disc Brake Rotor REAR CALIPER OPERATION AND WEAR COMPENSATION Rear disc caliper operation is the same as for front disc brakes. Refer to the information in the front disc brake section. REAR BRAKESHOE REMOVAL (1) Raise and support vehicle. (2) Remove rear wheels and tires. (3) Press caliper piston back into caliper bore with large C-clamp (Fig. 3). Fig. 1 Rear Disc Brake Caliper Mounting The rotor and splash shield used for rear discbrake applications are unique. The parking brake-shoes are mounted on the splash shield. The discbrake rotor has a built in brake drum surface for theparking brakeshoes (Fig. 2). Parking brakeshoe ser-vice is covered in the parking brake service section.Changes For 1995 The rear brakeshoes, caliper, and caliper bracketare different for 1995. The outboard shoe now has ananti-rattle spring attached at the shoe rear. A wearstrip has been added to the inboard shoe and the cal- Fig. 3 Bottoming Rear Caliper Piston In Bore
5 - 42 REAR DISC BRAKES ZJ (4) Remove caliper mounting bolts with ratchet REAR BRAKESHOE INSTALLATIONhandle and 13 mm socket (Fig. 4). (1) Clean brakeshoe contact surfaces of caliper mounting bracket (Fig. 6). Use wire brush or emery cloth. Fig. 6 Brakeshoe Contact Surfaces Of Mounting Bracket Fig. 4 Rear Caliper Mounting Bolt Removal/ Installation (2) Install brakeshoes in caliper. (3) Install caliper over rotor and into mounting (5) Rotate caliper rearward and off rotor (Fig. 5). bracket. (6) Remove outboard brakeshoe from caliper (Fig. (4) Verify that brakeshoe lugs are properly seated5). Press one corner of shoe inward then pry shoe up- on caliper mounting bracket (Fig. 7). Be sure springsward with suitable tool and rotate shoe out of caliper. on outboard shoes are also seated against bracket. (7) Remove inboard brakeshoe (Fig. 5). Pry shoeoutward until shoe retainers come out of caliper pis-ton. Then remove shoe from caliper. Fig. 7 Correct Brakeshoe Position On Bracket (Right Rear Caliper Shown) Fig. 5 Rear Caliper Removal (From Rotor) (5) Check rear brake hose position (Fig. 8). Hose (8) Support caliper with wire attached to nearby must not be twisted or kinked.suspension component. Do not allow brake hose to (6) Lubricate and install caliper mounting bolts.support caliper weight. Start bolts by hand then tighten bolts to 10-20 N⅐m (9) Wipe caliper off with shop rags or towels. Do (7-15 ft. lbs.) torque.not use compressed air. Compressed air can un- (7) Install wheel and tire assemblies. Tighten lugseat dust boot and force dirt into piston bore. nuts to 109-150 N⅐m (80-110 ft. lbs.) torque. (10) Inspect condition of caliper piston dust boot. (8) Turn ignition On and run HCU pump until itOverhaul caliper if evidence of leakage past piston shuts off. Then pump brake pedal until shoes areseal and dust boot is evident. seated and indicator lights go out. (11) Inspect caliper mounting bolt bushings and (9) Top off brake fluid level if necessary. Use Mo-boots. Replace boots if torn or cut. Replace bushings, par brake fluid or equivalent meeting SAE J1703 andor bolts if either exhibits wear, or heavy corrosion. DOT 3 standards only.
ZJ REAR DISC BRAKES 5 - 43 Fig. 10 Inboard Brakeshoe Removal Fig. 8 Rear Brake Hose PositionREAR CALIPER REMOVAL (1) Raise vehicle and remove wheels. (2) Remove caliper mounting bolts (Fig. 4). (3) Rotate caliper rearward by hand or with prytool. Then rotate caliper and brakeshoes off ledges ofmounting bracket. (4) Remove caliper fitting bolt and disconnect rearbrake hose at caliper. Discard metal washers on fit-ting bolt. Washers should be replaced and not reused. Fig. 11 Mounting Bolt Bushing And Boot Removal (5) Remove caliper from vehicle.REAR CALIPER DISASSEMBLY AND OVERHAUL (1) Remove outboard brakeshoe from caliper (Fig.9). Push one end of shoe inboard and pry shoe upwith tool to free shoe spring from caliper. (2) Remove inboard brakeshoe from caliper (Fig.10). Tilt shoe out until shoe spring is free of caliperpiston. Fig. 12 Padding Caliper Interior (For Piston Removal) CAUTION: Do not blow the piston out of the bore with sustained air pressure. This could result in a cracked piston. Use only enough air pressure to ease the piston out. In addition, NEVER attempt to catch the piston as it leaves the bore. This could re- sult in personal injury. (6) Remove caliper piston dust boot (Fig. 14). Use Fig. 9 Outboard Brakeshoe Removal suitable pry tool to remove boot. (3) Remove mounting bolt boots and bushings from (7) Remove and discard caliper piston seal withcaliper (Fig. 11). pencil, or plastic tool (Fig. 15). Do not use metal tools (4) Pad interior of caliper with minimum, one-inch as they will scratch piston bore.thickness of shop towels or rags (Fig. 12). Towels are CALIPER CLEANING AND INSPECTIONneeded to protect caliper piston during removal. Clean the caliper and piston with clean brake fluid (5) Remove caliper piston with short bursts of low or Mopar brake cleaning solvent only. Do not use gas-pressure compressed air. Direct air through fluid in-let port and ease piston out of bore (Fig. 13).
5 - 44 REAR DISC BRAKES ZJ iper if the bore is corroded, rusted, or scored. Do not hone the caliper piston bore. Replace the caliper if the bore is damaged. Inspect the caliper piston (Fig. 16). The piston is made from a phenolic resin and should be smooth and clean. Although surface discoloration is normal, replace the piston if cracked, chipped, or scored. Do not attempt to restore a scored piston surface by sanding or polishing. CAUTION: Never interchange phenolic resin and steel caliper pistons. The seals, seal grooves, cali- per bores and piston tolerances are different for resin and steel pistons. Do not intermix these com- ponents. Fig. 13 Caliper Piston Removal Inspect the caliper bushings and boots (Fig. 16). Replace the boots if cut or torn. Clean and lubricate the bushings with GE 661 or Dow 111 silicone grease if necessary. Replace the bolts if worn, or the threads are damaged. Fig. 14 Removing Caliper Piston Dust Boot Fig. 16 Rear Caliper Components REAR CALIPER ASSEMBLY (1) Lubricate caliper piston bore and new piston seal with clean brake fluid. (2) Install new piston seal in groove machined in piston bore. Be sure seal is fully seated and is not Fig. 15 Removing Caliper Piston Seal twisted. Press seal into place with fingertips. (3) Lubricate caliper piston with clean brake fluidoline, kerosene, thinner, or similar fluids. Theseproducts may leave a residue that could damage the and start piston into bore and seal by hand. Use apiston and seal. twisting, rocking motion to start piston into seal. Wipe the caliper and piston dry with lint free tow- Keep piston level while starting it in seal other-els or use low pressure compressed air. wise seal can be folded over. Inspect the piston and piston bore. Replace the cal-
ZJ REAR DISC BRAKES 5 - 45 (4) Once piston is firmly started in seal, press pis-ton about 2/3 of way into bore with C-clamp or benchvise (Fig. 17).CAUTION: Position a protective wood block be-tween the piston and C-clamp or vise jaws (Fig. 18).The wood block will avoid chipping or cracking thepiston while pressing it into place. Fig. 19 Seating Caliper Piston Dust Boot Fig. 17 Piston Installed Part Way In Caliper Bore Fig. 20 Mounting Bolt Bushing Boots Centered In Caliper Fig. 18 Using Wood Block To Protect Piston (5) Install dust boot on piston. Be sure boot lip isfully seated in groove at top of caliper piston. (6) Seat dust boot in caliper either by hand, orwith a suitable size installer tool (Fig. 19). (7) Press caliper to bottom of bore after seatingdust boot. Be sure to use wood block to protect pistonand boot. Fig. 21 Mounting Bolt Bushings Installed In Boots (8) Install caliper bleed screw, if removed. (9) Install bushing and boot assemblies in caliper. (13) Install inboard brakeshoe in caliper (Fig. 22).Be sure boots are centered in caliper as shown (Fig. Be sure shoe spring is fully seated in caliper piston.20). (14) Install outboard brakeshoe in caliper (Fig. 23). (10) Apply GE or Dow silicone grease to interior of Seat one end of shoe spring in caliper and rotate andbushing boots. Then apply same lubricant to exterior snap shoe into place. Be sure both ends of shoeand interior of bushings. spring are firmly seated in caliper. (11) Install mounting bolt bushings in boots (Fig. (15) If caliper will not be installed immediately,21). Be sure boot lips are seated in grooves at ends of cover caliper assembly with clean shop towels.bushings. (12) Center bushing boots in caliper.
5 - 46 REAR DISC BRAKES ZJ (2) Position caliper over rotor and into bracket. Be sure brakeshoe tabs are properly seated on mounting bracket ledges. (3) Connect rear brake hose to caliper. Use new washers on hose fitting. Tighten hose fitting bolt to 24-38 N⅐m (216-336 in. lbs.) torque. (4) Check brake hose position before proceeding. Verify that hose is not twisted, kinked, or touching any suspension components. (5) Lubricate and install caliper mounting bolts. Start bolts by hand then tighten bolts to 10-20 N⅐m Fig. 22 Inboard Brakeshoe Installation (7-15 ft. lbs.) torque. CAUTION: If new caliper bolts are being installed, or if the original reason for repair was a drag/pull condition, check caliper bolt length before proceed- ing. If the bolts have a shank length greater than 67.6 mm (2.66 in.), they will contact the inboard brakeshoe causing a partial apply condition. Refer to Figure 25 for required caliper bolt length. Fig. 23 Outboard Brakeshoe InstallationREAR CALIPER INSTALLATION (1) Verify that brakeshoes, boots and bushings arecorrectly positioned in caliper (Fig. 24). Fig. 25 Caliper Mounting Bolt Dimensions (6) Fill and bleed brake system. Refer to bleeding procedure in brake adjustments section. (7) Install wheel and tire assemblies. Tighten lug nuts to 109-150 N⅐m (80-110 ft. lbs.) torque. (8) Lower vehicle. REAR ROTOR REMOVAL (1) Raise vehicle. (2) Remove wheel and tire assembly. (3) Bottom caliper piston in bore with C-clamp, or screwdriver. Then remove caliper mounting bolts and slide caliper off rotor. Secure caliper to spring or sus- pension arm with wire. (4) Remove access plug from splash shield and back off parking brakeshoes by rotating adjuster screw star wheel with brake tool (Fig. 26). At driver side rear wheel, rotate adjuster screw star wheel Fig. 24 Shoe/Bushing/Boot Position In Caliper clockwise to back off shoes. At passenger side wheel,
ZJ REAR DISC BRAKES 5 - 47rotate star wheel in counterclockwise direction. Di-rection of rotation is while looking from rear to frontof vehicle. Fig. 27 Parking Brakeshoe Inspection (4) Install wheel and tire assembly and lower vehi- cle. (5) Adjust parking brakeshoes. Use brake tool to rotate adjuster screw star wheel. Tighten shoes until Fig. 26 Backing Off Parking Brake Shoes light drag is created. Then back off shoes about 1/2 to (5) If rotor and/or axle hub contact surfaces are one turn of star wheel.heavily rusted, apply Mopar rust penetrant to rotor (6) Install plug in splash shield access hole.and axle hub and through spaces around wheel (7) Pump brake pedal to seat caliper piston andstuds. brakeshoes. Do not move vehicle until firm brake pedal is obtained. (6) Remove push nuts securing rotor to axle shaftstuds. WHEEL NUT TIGHTENING (7) Work rotor off axle hub and studs. Use plastic The wheel attaching nuts must be tightened prop-or rawhide mallet to loosen rotor if necessary. erly to ensure efficient brake operation. Overtighten- (8) Clean and inspect rotor braking surfaces. Re- ing the nuts or tightening them in the wrongfinish, or replace rotor if necessary. sequence can cause distortion of the brake rotors and (9) Inspect condition of parking brakeshoes (Fig. drums.27). Replace shoes if worn to thickness of 1.6 mm Impact wrenches are not really recommended for(0.063 in.). Refer to procedures in Parking Brake ser- tightening wheel nuts. A torque wrench is preferredvice section. for this purpose. Correct tightening torque is 109-150 N⅐m (80-110 ft. lbs.).REAR ROTOR INSTALLATION The correct tightening sequence is important in (1) Clean axle hub and hub bore in rotor with wire avoiding rotor and drum distortion. The correct se- quence is in a diagonal crossing or star pattern. Seatbrush, or emery cloth. the wheel and install the wheel nuts finger tight. (2) Install rotor on axle hub. Tighten the nuts in sequence to half the required (3) Install disc brake caliper. Refer to procedure in torque. Then repeat the tightening sequence to finalthis section. specified torque.
5 - 48 DISC BRAKE ROTOR SERVICE ZJ DISC BRAKE ROTOR SERVICE INDEX page pageChecking Front Rotor Thickness . . . . . . .. . . . . . . 48 Checking Rotor Lateral Runout . . . . . . . . . . . . . . . 49Checking Front Rotor Thickness Variation . . . . . . . 48 Rear Disc Brake Rotor Usable Thickness . . . . . . . . 49Checking Rear Rotor Lateral Runout . . . .. . . . . . . 50 Rotor Refinishing . . . . . . . . . . . . . . . . . . . . . . . . . 48Checking Rear Rotor Thickness . . . . . . .. . . . . . . 49ROTOR REFINISHING Rotor braking surfaces can be refinished by sand-ing and/or machining in a disc brake lathe. Machin-ing can be performed on, or off the vehicle. Use astandard lathe, or one of the newer style, portablelathes. The new portable lathes machine the rotorwhile in place on the vehicle. The disc brake lathe must be capable of machiningboth rotor surfaces simultaneously with dual cutterheads (Fig. 1). Equipment capable of machiningonly one side at a time will produce a taperedrotor. The lathe should also be equipped with agrinder attachment or dual sanding discs for finalcleanup or light refinishing. If the rotor surfaces only need minor cleanup ofrust, scale, or minor scoring, use abrasive discs toclean up the rotor surfaces. However, when a rotor isscored or worn, machining with cutting tools will berequired.CAUTION: Do not refinish a rotor if machiningwould cause the rotor to fall below minimum allow-able thickness. The final finish on the rotor should be a non-direc-tional, cross hatch pattern (Fig. 2). Use sanding discsto produce this finish. The final finish on the rotor should be a non-direc-tional, cross hatch pattern. Use sanding discs to pro-duce this finish.CHECKING FRONT ROTOR THICKNESS Rotor minimum usable thickness is 22.7 mm (0.89in.). Do not resurface a rotor if machining wouldcause thickness to fall below this limit. Measure rotor thickness at the center of the brake-shoe contact surface. Replace the rotor if worn belowminimum thickness, or if refinishing would reducethickness below the allowable minimum.CHECKING FRONT ROTOR THICKNESS VARIATION Variations in rotor thickness will cause pedal pul-sation, noise and shudder. Measure rotor thickness at four to six pointsaround the rotor face. Position the micrometer ap- Fig. 1 Typical Rotor Refinishing Equipment
ZJ DISC BRAKE ROTOR SERVICE 5 - 49 Fig. 4 Securing Rotor For Runout Check Fig. 2 Preferred Rotor Surface Finishproximately 3/4 inch from the rotor outer circumfer-ence for each measurement (Fig. 3). Thickness should not vary by more than 0.013 mm(0.0005 in.) from point to point on the rotor. Refinishor replace the rotor if necessary. Fig. 5 Checking Rotor Lateral Runout REAR DISC BRAKE ROTOR USABLE THICKNESS Minimum usable thickness of the rear disc brake rotor is 9.5 mm (0.374 in.). The thickness specifica- tion is located on the edge of the parking brake drum section of the rotor (Fig. 6). Never resurface a rotor if machining would cause thickness to fall below this limit. Measure rotor thickness at the center of the brake- shoe contact surface. Replace the rotor if worn below Fig. 3 Measuring Rotor Thickness Variation minimum thickness, or if refinishing would reduce thickness below the allowable minimum.CHECKING ROTOR LATERAL RUNOUT Check rotor lateral runout whenever pedal pulsa- CHECKING REAR ROTOR THICKNESStion, or rapid, uneven brakelining wear has occurred. Variations in rotor thickness will cause pedal pul- The rotor must be securely clamped to the hub to sation, noise and shudder.ensure an accurate runout measurement. Secure the Measure rotor thickness at four to six pointsrotor with the wheel nuts and 4 or 5 large diameter around the rotor face. Position the micrometer ap-flat washers on each stud as shown (Fig. 4). Use a dial indicator to check lateral runout (Fig. 5). proximately 3/4 inch from the rotor outer circumfer- Maximum allowable rotor lateral runout is 0.13 ence for each measurement.mm (0.005 in.).
5 - 50 DISC BRAKE ROTOR SERVICE ZJ CHECKING REAR ROTOR LATERAL RUNOUT Check rotor lateral runout whenever diagnosis in- dicates pedal pulsation and rapid, uneven brakelin- ing wear. On 4-wheel drive models, the rotor must be se- curely clamped to the hub to ensure an accurate runout measurement. Secure the rotor with the wheel nuts and 4 or 5 large diameter flat washers on each stud as shown (Fig. 5). Use a dial indicator to check lateral runout (Fig. 5). Maximum allowable lateral runout is 0.13 mm (0.005 in.).Fig. 6 Location Of Thickness Specification On Rear Rotor Thickness should not vary by more than 0.0254mm (0.001 in.) from point to point on the rotor. Re-finish or replace the rotor if necessary.
ZJ PARKING BRAKES 5 - 51 PARKING BRAKES INDEX page pageCam and Lever Replacement . . . . . . . . . . . . . . . . 58 Parking Brake Rear Cable Installation . . . . . . . . . . 55General Service Information . . . . . . . . . . . . . . . . . 51 Parking Brake Rear Cable Removal . . . . . . . . . . . 55Parking Brake Front Cable Installation . . . . . . . . . . 54 Parking Brake Tensioner Adjustment . . . . . . . . . . . 55Parking Brake Front Cable Removal . . . . . . . . . . . 53 Parking Brakeshoe Adjustment . . . . . . . . . . . . . . . 58Parking Brake Hand Lever Installation (With Full Parking Brakeshoe Installation . . . . . . . . . . . . . . . . 57 Console) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Parking Brakeshoe Removal . . . . . . . . . . . . . . . . . 56Parking Brake Hand Lever Installation (With Mini Parking Brakeshoe Replacement . . . . . . . . . . . . . . 56 Console) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Splash Shield/Caliper Bracket/Lever BootParking Brake Hand Lever Removal (With Full Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Console) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Parking Brake Hand Lever Removal (With Mini Console) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53GENERAL SERVICE INFORMATION the second, is when the tensioner and cables The parking brakes on Grand Cherokee models are are disconnected for access to other brake com-operated by a cable and hand lever system. Three ca- ponents.bles are used, consisting of one front cable and tworear cables. The hand lever is mounted on the floor-pan adjacent to the driver (Fig. 1). All three cables are interconnected at the cable ten-sioner and equalizer mechanism. The front cable isconnected to the hand lever and the rear cables areconnected to the brakeshoes. Cable adjustment isperformed at the tensioner which is attached to thefront cable.Parking Brake Systems A separate set of brakeshoes are used for parkingbrake operation. The shoes are mounted on the discbrake splash shield and are enclosed within the com-bination disc brake rotor and parking brake drum(Fig. 2). On these models, the rear cables are con-nected to a cam and lever mechanism. It is the camand lever that operates the shoes on these models.Rear Cable Attachment The cable is connected to the lever by a rectangulareyelet on the cable end (Fig. 3). A retainer on the ca-ble secures it in a bracket attached to the rear of thecaliper bracket.Parking Brake Cable Tensioner Adjustment Parking brake cable adjustment is controlledby a tensioner mechanism. This applies to ZJ Fig. 1 Parking Brake Hand Lever Mounting (All)models from 1992 to current. The cable ten-sioner, once adjusted at the factory, will not PARKING BRAKE HAND LEVER REMOVAL (WITHneed further adjustment under normal circum- FULL CONSOLE)stances. There are only two instances when ad- (1) Release parking brakes.justment is required. The first is when a new (2) Disconnect battery negative cable.tensioner, or cables have been installed. And (3) Remove screws at bottom of console storage bin (Fig. 4).
5 - 52 PARKING BRAKES ZJ Fig. 4 Full Console Rear Attaching Screw Location Fig. 2 Parking Brake Components Fig. 5 Full Console Front Attaching Screw Location (12) Disconnect and remove air bag control module (Fig. 6). (13) Disconnect parking brake switch wires. (14) Remove parking brake lever attaching screws. Fig. 3 Rear Cable Attachment At Lever (15) Disengage front cable from parking brake le- (4) On models with automatic transmission, re- ver and remove lever assembly.move handle from transmission shift lever. Grasphandle and pull up sharply to remove handle from le- PARKING BRAKE HAND LEVER INSTALLATIONver. (WITH FULL CONSOLE) (5) Unsnap and remove shift lever bezel (Fig. 5). (1) Attach front cable to parking brake lever.Bezel has two retainer tabs on each side. (2) Install parking brake lever on floorpan. (6) Remove bulb from shift lever bezel. (3) Connect parking brake switch wires to lever. (7) Remove screws attaching front of console. (4) Install air bag control module and connect allScrews are under shift lever bezel and are accessible wires to module.once bezel has been removed. (5) Install console over shift levers and on mount- (8) Remove bezel under parking brake lever. ing brackets and floorpan. (9) Move transmission and transfer case shift le- (6) Install bulbs in shift lever bezels.vers rearward. (7) Install console attaching screws. (10) Raise front of console and remove bulb at rear (8) Install transmission shift lever bezel and in-of transfer case shift lever bezel. stall bezel under parking brake lever. (11) Remove console by lifting it upward and off (9) Align and install shift handle on transmissionshift levers. shift lever.
ZJ PARKING BRAKES 5 - 53 (10) Adjust parking brake cable if a new tensioner (7) Unsnap and remove cup holder from parkinghas been installed. brake lever cover (Fig. 8). (11) Lower vehicle. (8) Remove screws attaching lever cover to floor (12) Connect battery negative cable. pan and remove cover (Fig. 8). (9) Disconnect wires at parking brake switch and at air bag module (Figs. 5 and 8). Note that air bag module has two sets of wires connected to it. (10) Remove screws attaching air bag control mod- ule to floorpan and parking brake lever (Figs. 8 and 9). Then move module aside for access to lever. (11) Remove screws attaching parking brake lever to bracket (Fig. 10) and lift lever upward for access to front cable. (12) Disengage front cable from parking brake le- ver and remove lever assembly from vehicle. PARKING BRAKE HAND LEVER INSTALLATION (WITH MINI CONSOLE) (1) Connect front cable to lever assembly. (2) Seat front cable in floor pan. (3) Install lever assembly on mounting bracket (Fig. 8). (4) Connect parking brake switch wire. (5) Install air bag control module (Fig. 6). Be sure all module wires harnesses are securely connected. Fig. 6 Air Bag Control Module Mounting (6) Install parking lever cover. (7) Install cup holder in cover.PARKING BRAKE HAND LEVER REMOVAL (WITH (8) Raise vehicle.MINI CONSOLE) (9) Assemble front cable, cable tensioner and cable (1) Release parking brakes if applied. bracket. (2) Disconnect battery negative cable. (10) Adjust parking brake front cable. Refer to pro- (3) Raise vehicle on hoist. cedure in this section. (4) Remove front cable adjusting nut and disen- (11) Lower vehicle.gage cable tensioner from equalizer. Then remove (12) Connect battery negative cable.front cable from tensioner (Fig. 7). (5) disengage front cable from insert and insert PARKING BRAKE FRONT CABLE REMOVALfrom floorpan (Fig. 7). (1) Release parking brakes, if applied. (2) Disconnect battery negative cable and raise ve- hicle on hoist. (3) Remove front cable adjusting nut and disen- gage cable tensioner from equalizer. Then remove front cable from tensioner (Fig. 7). (4) disengage front cable from insert and insert from floorpan (Fig. 7). (5) Lower vehicle. (6) On models with full console, remove console. Refer to parking brake lever removal procedure for full console. (7) On models with mini console, unsnap and re- move cup holder from parking brake lever cover (Fig. 8). Then remove screws attaching lever cover to floor pan and remove cover. (8) Disconnect wires at parking brake switch and Fig. 7 Parking Brake Front Cable Attachment at air bag module (Figs. 6 and 10). Note that air bag (6) Lower vehicle. module has two sets of wires connected to it.
5 - 54 PARKING BRAKES ZJ Fig. 8 Mini Console Components (10) Remove screws attaching parking brake lever to bracket and lift lever upward for access to front cable. (11) Disconnect front cable from parking brake le- ver and remove cable. PARKING BRAKE FRONT CABLE INSTALLATION (1) Connect front cable to lever assembly. (2) Seat front cable in floor pan. (3) Install lever assembly on mounting bracket. (4) Connect parking brake switch wire. (5) Install air bag control module. Be sure all mod- ule wires harnesses are securely connected. (6) Install parking lever cover. (7) Install cup holder in cover. (8) Raise vehicle. (9) Assemble front cable, cable tensioner and equalizer. (10) Adjust parking brake system if new cable, or tensioner has been installed, or if tensioner mecha- nism has been loosened, or removed for access to Fig. 9 Parking Brake Lever Mounting other components. Refer to Parking Brake Adjust- ment procedure in this section. (9) Remove screws attaching air bag control mod- (11) Lower vehicle.ule to floorpan and parking brake lever. Then move (12) Disconnect battery negative cable.module aside for access to lever.
ZJ PARKING BRAKES 5 - 55 PARKING BRAKE REAR CABLE INSTALLATION (1) Install cable eyelet on lever. Be sure eyelet is seated in lever notch. (2) Seat cable retainer in caliper bracket. (3) Route cable up to cable tensioner and equalizer. Then connect cable to equalizer. (4) Check cable routing. Be sure cable is secured in body and chassis clips and retainers. Also be sure ca- ble is not twisted, kinked or touching any rotating components. (5) Adjust parking brake front cable as described in following procedure. PARKING BRAKE TENSIONER ADJUSTMENT Parking brake tensioner adjustment is only necessary when the tensioner, or a cable has been replaced or disconnected for service. When adjustment is necessary, perform adjust- ment only as described in the following proce- dure. This is necessary to avoid faulty parking brake operation. (1) Raise vehicle. (2) Back off tensioner adjusting nut at equalizer to create slack in cables. (3) Remove rear wheel/tire assemblies. Then re- move calipers and rotors. (4) Adjust parking brake shoes as follows:Fig. 10 Parking Brake Lever And Cable Attachment (a) Replace worn parts if necessary. ExcessivePARKING BRAKE REAR CABLE REMOVAL shoe-to-drum clearance, or worn cam and le- (1) Raise vehicle and loosen adjusting nut at equal- ver components will result in faulty parkingizer to provide slack in rear cables. brake adjustment and operation. (2) Disengage cable at equalizer. Then disengage (b) Verify that parking brake cables operatecable from body and chassis clips and retainers. freely and are not binding, or seized. Replace faulty (3) Slide cable eyelet off actuating lever (Fig. 11). cables, or cam and lever before proceeding. (c) Install rotors if removed. (d) Adjust parking brakeshoes to drum surface in rotor by turning adjuster screw star wheel with brake tool. Verify that rotor assembly rotates freely without drag. (e) Install calipers. (5) Reinstall wheel/tire assemblies after brakeshoe adjustment is complete. (6) Lower vehicle enough for access to parking brake lever or foot pedal. Then fully apply parking brakes. Leave brakes applied until adjustment is complete. (7) Raise vehicle again. (8) Mark tensioner rod 6.5 mm (1/4 in.) from ten- sioner bracket (Fig. 12).Fig. 11 Parking Brake Cable Attachment (With Disc (9) Tighten adjusting nut at equalizer until Brakes) mark on tensioner rod moves into alignment (4) Compress retainer securing cable in bracket at- with tensioner bracket (Fig. 12).tached to caliper bracket. Then remove cable from CAUTION: Do not loosen, or tighten the tensionerbracket. adjusting nut for any reason after completing ad- justment.
5 - 56 PARKING BRAKES ZJ (10) Lower vehicle until rear wheels are 15-20 cm(6-8 in.) off shop floor. (11) Release parking brake hand lever and verifythat rear wheels rotate freely without drag. Thenlower vehicle. Fig. 13 Retracting Parking Brake Shoes (With Rear Disc Brakes) (9) Tap rotor a few times with plastic or rubber mallet to loosen it. Then remove rotor from axle hub flange and park brake shoes (Fig. 14).Fig. 12 Placing Adjustment Mark On Tensioner Rod (10) Remove rear shoe holddown clip and pin (Fig. 14). Clip is held in place by pin which fits in clipPARKING BRAKESHOE REPLACEMENT notch. To remove clip, first push clip ends together A drum style, dual-shoe parking brake mechanism with thumb or forefinger. Next, slide clip upward un-is used on all models. The shoes are expanded me- til head of pin clears narrow part of notch. Then re-chanically by a cable operated cam and lever. move pin and clip. The braking surface for the parking brake shoes iscast into the central hub of the rear disc brake rotor.The shoes are mounted on the splash shield and se-cured with holddown clips and return springs. A cam and lever mechanism is used to expand thepark brake shoes. The levers are connected to andoperated by the parking brake rear cables.PARKING BRAKESHOE REMOVAL (1) Raise vehicle. (2) Remove rear wheel and tire assembly. (3) Apply Mopar rust penetrant all around jointformed by axle hub and disc brake rotor. Then applypenetrant through stud holes in rotor. This will helploosen any corrosion buildup that may have formedand ease rotor removal. (4) Press caliper piston back into caliper bore withlarge C-clamp or screwdriver. (5) Remove caliper mounting bolts with ratchetand 13 mm socket. (6) Rotate caliper rearward and off rotor. Do notallow brake hose to support caliper weight.Support caliper with wire attached to suspen-sion component. (7) Remove rubber access plug from back of reardisc brake splash shield. (8) Retract parking brakeshoes. Use standardbrake tool to rotate adjuster screw star wheel (Fig.13). Position tool at top of star wheel and rotate Fig. 14 Rear Shoe Holddown Clip And Pin Removalwheel downward in clockwise direction (while facingfront of vehicle).
ZJ PARKING BRAKES 5 - 57 (11) Disengage lower spring from rear shoe withneedle nose pliers (Fig. 15). Fig. 18 Front Brakeshoe And Holddown Clip And Pin Removal (16) Clean and inspect condition of adjuster screw assembly. Replace assembly if worn, or damaged in any way. (17) Inspect condition of park brake cam and lever. If these parts are worn, replace both parts as an as-Fig. 15 Disengaging Lower Spring From Rear Shoe sembly. Note position of cam and lever for in- (12) Tilt rear shoe outward and remove spring and stallation reference.adjuster screw (Fig. 16). Note spring and adjuster (18) Clean splash shield with Mopar brake cleanerscrew position for installation reference. and note condition of shoe contact pads (Fig. 19). Re- place shield if any pad surfaces are worn through. Refer to Splash Shield/Caliper Bracket/Lever Boot re- placement procedure in this section. (19) Note condition of cam and lever dust boot. If boot is cut, torn, folded over, or mispositioned, re- place boot. Refer to Splash Shield/Caliper Brack- et/Lever Boot replacement procedure in this section as boot position is important to proper rotor to splash shield clearance. (20) Clean and inspect rotor. Minor surface corro- sion, nicks, or scratches can be reduced with 180 grit emery cloth. Replace rotor if either braking surface is Fig. 16 Lower Shoe Spring And Adjuster Screw scored, or worn. Do not machine the rotor. Removal (13) Disengage upper spring from front shoe andremove rear shoe and upper spring (Fig. 17).Fig. 17 Rear Brakeshoe And Upper Spring Removal (14) Remove front shoe holddown clip and pin. Fig. 19 Shoe Contact Pad Locations On SplashThen remove front shoe (Fig. 18). Shield (15) Inspect condition of shoe springs, holddown PARKING BRAKESHOE INSTALLATIONclips and pins. Replace these parts if bent, distorted, (1) Lubricate shoe contact pads and cam and leveror heat damaged. with Mopar multi-mileage grease.
5 - 58 PARKING BRAKES ZJ (2) Install shoes on splash shield. Use new hold- Lever/Cam Interchangeability And Correct Positiondown clips and pins to secure shoes if necessary. Be The cams are reversible and can be used at eithersure shoes are properly engaged in caliper bracket wheel.and cam. The levers are NOT reversible. They are marked R (3) Lubricate adjuster screw threads with Mopar and L to identify them and must only be used on thespray lube, LPS all purpose lube, or equivalent. Be correct wheel.sure star wheel turns freely. Correct lever position is important. The lever notch (4) Install adjuster screw assembly. Be sure (for the cable eyelet), faces rearward on both sides. Innotched ends of screw assembly are properly seated addition, be sure the R side is facing up on the pas-on shoes and that star wheel is aligned with access senger side and the L side is facing up on the driverhole in shield. side. (5) Install shoe lower return spring. Needle nosepliers can be used to connect spring to each shoe. Replacement Procedure (6) Install shoe upper return spring. Engage short (1) Raise vehicle.end of spring in front shoe. Then use pointed tool (2) Remove wheel and tire assembly.with 20-25 cm (8-10 in.) long shank to engage spring (3) Remove disc brake caliper.in rear shoe. (4) Remove parking brakeshoes. (7) Check shoe installation. Operate lever to verify (5) Move lever forward and disconnect parkingthat shoes expand and retract properly. brake rear cable from lever. (8) Install rotor. (6) Pull lever forward through boot. Disengage cam (9) Install caliper over rotor and into bracket. from lever and remove cam (Fig. 20). Note cam posi- (10) Adjust parking brakeshoes. Refer to procedure tion for installation reference.in this section. (7) Remove lever. (11) Lubricate caliper mounting bolts with lightcoat of Dow or GE silicone grease. Then install andtighten bolts to 10-20 N⅐m (7-15 ft. lbs.) torque. (12) Install wheel and tire assembly. (13) Adjust parking brake cable tensioner. Refer toParking Brake Tensioner Adjustment procedure inthis section. (14) Lower vehicle and verify correct parking brakeoperation.PARKING BRAKESHOE ADJUSTMENT (1) Install rotor, if removed. Temporarily secure ro-tor with one or two wheel nuts. Fig. 20 Parking Brake Cam, Lever And Boot (2) Remove rubber access plug from back of splash (8) Lubricate replacement lever with GE or Dowshield. silicone grease. Then insert lever part way through (3) Insert brake tool through access hole in splash boot. Be sure lever notch is facing rearward.shield (Fig. 11). Position tool at bottom of star wheel. (9) Engage cam in lever. Then simultaneously slide (4) Rotate star wheel upward in counterclockwise cam into place on splash shield and work leverdirection to expand shoes (while facing front of vehi- through boot.cle). (10) Install parking brakeshoes. (5) Expand shoes until light drag is experienced. (11) Verify correct installation of cam and lever byThen back off adjuster screw only enough to elimi- pulling lever toward front of vehicle. Cam should ex-nate drag. pand both brakeshoes as lever is pulled forward. (6) Install plug in splash shield access hole. (12) Install rotor and adjust parking brakeshoes. Refer to procedure in this section.CAM AND LEVER REPLACEMENT (13) Connect rear cable to lever. Be sure cable eye- The cam and lever that operates each set of park- let is securely attached in lever notch.ing brakeshoes are serviceable parts. (14) Install brake caliper and wheel and tire as- The lever boot should also be inspected and ser- sembly.viced when necessary. Replace the boot if cut, torn, or (15) Lower vehicle and verify correct parking brakefolded over (mispositioned). Refer to the Splash operation.Shield/Caliper Bracket/Lever Boot Replacement pro-cedure in this section.
ZJ PARKING BRAKES 5 - 59SPLASH SHIELD/CALIPER BRACKET/LEVER BOOTREPLACEMENT The splash shield and caliper bracket are now rivetedtogether at the factory. The rivets only ensure that theparking brake lever boot is not displaced during assem-bly operations. Although the rivets must be drilled outfor shield, bracket, or boot replacement, it is not nec-essary to install new rivets afterward. (1) Raise vehicle and remove appropriate wheeland tire assembly. (2) Remove caliper bolts and lift caliper off rotorand bracket. Suspend caliper from chassis or suspen-sion component with wire. (3) Retract parking brakeshoes and remove rotor. (4) Remove axle shaft. Refer to Group 3 for proce-dure. Fig. 22 Drilling Out Splash Shield Rivets (5) Remove parking brakeshoes from splash shield. (6) Remove nuts attaching splash shield and cali-per bracket to axle tube flange. (7) Remove splash shield and caliper bracket fromaxle studs and work lever out of rear cable eyelet. (8) Mark position of splash shield and bracket forassembly reference (Fig. 21). Use paint or scriber tomark parts. Fig. 23 Caliper Bracket, Splash Shield And Lever Boot Fig. 21 Marking Position Of Splash Shield And grit paper. Lubricate pad surfaces with light coat of Bracket Mopar multi-mileage grease. (9) Drill out rivets that retain splash shield to cal- (13) Apply thin coat of contact cement or siliconeiper bracket (Fig. 22). If rivet heads did not come adhesive to new lever boot and to boot mounting areacompletely off after drilling, remove remaining pieces of caliper bracket (Fig. 24). Apply adhesive to areaswith small chisel. Note that the rivets do not where boot and bracket contact one another. Adhe-have to be replaced at installation. The rivets sive is needed to hold boot in position when splashare only used during manufacture to keep the shield is attached to bracket.boot in place during handling. (14) Install new boot on caliper bracket. Metal re- (10) Note position of cam and lever for installation tainer part of boot fits over ledge on caliper as shownreference. Then remove cam and lever from splash (Fig. 25). Rubber part of boot extends through rearshield and bracket. opening in bracket. Allow adhesive on boot and bracket (11) Separate splash shield and caliper bracket. to set up for a minute or two before proceeding.Then remove lever boot from bracket (Fig. 23). (15) Position splash shield on caliper bracket. Then (12) If original bracket and shield will be reused, carefully install shield and bracket assembly on axleclean them with Mopar carb and brake cleaner. Also tube flange studs.clean shoe contact pad surfaces of shield with 400
5 - 60 PARKING BRAKES ZJ Fig. 24 Applying Adhesive To Parking Brake Lever Boot Fig. 26 Cam And Lever Installation Fig. 25 Lever Boot InstallationCAUTION: Be sure the parking brake lever boot is notdisplaced when the shield/assembly is installed. If theboot becomes mispositioned, it will prevent the shieldfrom seating squarely on the bracket. This will cock theshield causing it to rub against the rotor after installation.Inspect the boot and reposition it if necessary. (16) Apply Mopar Lock N’ Seal (or Loctite 242), toaxle tube stud nuts. Then install and tighten nuts to43-61 N⅐m (32-45 ft. lbs.) torque. (17) Assemble and install cam and lever. Push lever Fig. 27 Parking Brakeshoes Mounted On Shieldthrough boot and seat cam between lip on shield andledge on bracket (Fig. 26). Then engage lever in cableeyelet. Be sure cable notch in lever is facing rearward.Remove and reposition cam and lever if necessary. (18) Install parking brakeshoes on splash shield.Verify positioning of cam and lever, shoes, springsand holddown clips and pins (Fig. 27). (19) Verify correct positioning of caliper bracketand shield (Fig. 28). Caliper opening and ledgesshould be to rear as shown. (20) Install axle shaft, shaft retainer clips and hous-ing cover. Check lube level and add lubricant if needed. (21) Install rotor, caliper, and wheel and tire as-sembly. Then adjust parking brakeshoes. (22) Lower vehicle and verify correct service andparking brake operation. Fig. 28 Checking Caliper Bracket And Shield Position
ZJ BRAKE PEDAL AND BRAKELIGHT SWITCH 5 - 61 BRAKE PEDAL AND BRAKELIGHT SWITCH INDEX page pageBrake Pedal Installation . . . . . . . . . . . . . . . . . . . . . 61 Brakelight Switch Removal . . . . . . . . . . . . . . . . . . 62Brake Pedal Removal . . . . . . . . . . . . . . . . . . . . . . 61 Brakelight Switch Test and Diagnosis . . . . . . . . . . . 62Brake Pedal Service . . . . . . . . . . . . . . . . . . . . . . . 61 General Information . . . . . . . . . . . . . . . . . . . . . . . 61Brakelight Switch Adjustment and Installation . . . . . 62GENERAL INFORMATION (4) Remove retainer clip and washers attaching A suspended-type brake pedal is used on all models booster push rod to pedal pin (Fig. 1).(Fig. 1). The pedal pivots on a pin mounted in the (5) Remove nut securing pedal shaft in supportpedal support bracket. The bracket is attached to the bracket.dash and instrument panels on all models. (6) Slide pedal shaft outward for clearance and re- A plunger-type, self adjusting brakelight switch is move brake pedal.used on all models. The switch is attached to a flange (7) Remove pedal bushings if they are to be re-on the pedal support bracket. placed.BRAKE PEDAL SERVICE BRAKE PEDAL INSTALLATION The brake pedal is a serviceable component. The (1) Install new bushings in pedal. Lubricate bush-pedal, pivot pin, sleeve, pedal bushings and spacers/ ings and pivot pin with Mopar multi-mileage grease.washers are all replaceable parts. The pedal bracket (2) Position pedal, sleeve and spacer(s) in bracketcan also be replaced when necessary. and install pedal shaft in support and through pedal. (3) Install new nut on pedal shaft. Shaft nut isBRAKE PEDAL REMOVAL specially formed and should not be reused. Be (1) Remove lower trim panel and air conditioning sure to install new nut to secure shaft.duct if necessary. (4) ) Tighten pedal shaft nut to 27 N⅐m (20 ft. lbs.) (2) Remove steering column lower trim panel and on models with manual transmission. Tighten nut tobezel. (3) Remove necessary dash panel-to-instrument 35 N⅐m (26 ft. lbs.) on models with automatic trans-panel brace rods. mission. Fig. 1 Brake Pedal Mounting
5 - 62 BRAKE PEDAL AND BRAKELIGHT SWITCH ZJ (5) Install bushing on pedal pin if removed (Fig. 1). • Switch terminals 5 and 6 are for the brakelight (6) Install booster push rod on pedal pin. Secure circuitpush rod to pedal with retainer ring and washers. • Switch terminals 3 and 4 are for the speed control (7) Install dash brace rod, if equipped. circuit (8) Install instrument panel trim and air condition-ing duct if removed. (9) Check and adjust brakelight switch if neces-sary. Refer to procedure in this section.BRAKELIGHT SWITCH REMOVAL The brakelight switch is mounted on the pedal sup-port bracket. The switch plunger is actuated by astriker attached to the pedal. The switch is securedin the bracket means of a built-in retainer on theswitch body. (1) Remove steering column cover and lower trimpanel for switch access (if necessary). (2) Press brake pedal downward to fully appliedposition. (3) Rotate switch approximately 30° in counter- Fig. 3 Brakelight Switch Terminal Identification Andclockwise direction to unlock switch retainer. Then Plunger Test Positionpull switch rearward and out of bracket. Switch Continuity Test Procedure (4) Disconnect switch wire harness and remove (1) Check continuity between terminal pins 5 andswitch from vehicle (Fig. 2). 6 as follows: (5) Test switch as described in following procedure, (a) Pull plunger all the way out to fully extendedif necessary. position. (b) Attach test leads to pins 5 and 6 and note ohmmeter reading. (c) If continuity exists, proceed to next test. Re- place switch if meter indicates lack of continuity (shorted or open). (2) Check continuity between terminal pins 1 and 2 and pins 3 and 4 as follows: (a) Push switch plunger inward to fully retracted position. (b) Attach test leads to pins 1 and 2 and note ohmmeter reading. (c) If continuity exists, switch is OK. Replace switch if meter indicates lack of continuity (shorted or open). BRAKELIGHT SWITCH ADJUSTMENT AND Fig. 2 Brakelight Switch INSTALLATION (1) Pull switch plunger all the way out to fully ex-BRAKELIGHT SWITCH TEST AND DIAGNOSIS tended position. Brakelight switch operation can be tested with an (2) Connect harness wires to switch.ohmmeter. The ohmmeter is used to check continuity (3) Press and hold brake pedal in applied position.between the pin terminals at different plunger posi- (4) Install switch as follows: Align tab on switchtions (Fig. 3). with notch in switch bracket. Then insert switch in The switch wire harness must be discon- bracket and turn it clockwise about 30° to lock it innected before testing switch continuity. place. (5) Release brake pedal. Then pull pedal fully rear-Switch Circuit Identification ward. Pedal will set plunger to correct position as• Switch terminals 1 and 2 are for the brake sensor pedal pushes plunger into switch body. Switch willcircuit make racheting sound as it self adjusts.