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CHAPTER 10Drum Brakes
OBJECTIVES   After studying Chapter 10, the reader will be able to:   1.        Prepare for the Brakes (A5) ASE certificat...
KEY TERMS   •      Anchor eyes                     •   Lining fade   •      Beehive holddown                •   Lining tab...
DRUM BRAKE ADVANTAGES   •      Drum brakes were the first type of brakes used on          motor vehicles.   •      Even to...
DRUM BRAKE ADVANTAGES                            FIGURE 10–1 Typical brake system components showing disc                 ...
DRUM BRAKE ADVANTAGES                           FIGURE 10–2 An exploded view of a typical drum brake assembly.Automotive B...
DRUM BRAKE ADVANTAGES   •      SELF-ENERGIZING AND SERVO ACTION   •      PARKING BRAKE SERVICEAutomotive Brake Systems, 5/...
DRUM BRAKE DISADVANTAGES        BRAKE FADE   •      Drum brakes are not very efficient at dissipating          heat.   •  ...
DRUM BRAKE DISADVANTAGES        BRAKE FADE   •      The four types of brake fade include:            •    1. Mechanical Fa...
DRUM BRAKE DISADVANTAGES   •      BRAKE ADJUSTMENT   •      BRAKE PULLAutomotive Brake Systems, 5/e        Copyright © 201...
Quick-and-Easy Drum Brake Adjustment        Check          •     Tap the brake drum lightly with a hammer or              ...
DRUM BRAKE PARTS        BACKING PLATE   •      The foundation of every          drum brake is the backing          plate t...
DRUM BRAKE PARTS        BACKING PLATE                                FIGURE 10–4 A labyrinth seal is created between the l...
DRUM BRAKE PARTS        SHOE ANCHORS   •      Shoe anchors prevent the          brake shoes from rotating          with th...
DRUM BRAKE PARTS        PISTON STOPS   •      Some backing plates          incorporate piston stops          that prevent ...
DRUM BRAKE PARTS        SHOE SUPPORT PADS   •      The shoe support pads are stamped into the          backing plate and c...
DRUM BRAKE PARTS        WHEEL CYLINDERS   •      Hydraulic pressure is          transferred from the master          cylin...
DRUM BRAKE PARTS        WHEEL CYLINDERS                        FIGURE 10–8 The pushrods are held in place by the rubber du...
DRUM BRAKE SHOES   •      The linings of drum brakes          are attached to curved          metal assemblies called     ...
DRUM BRAKE SHOES                                                     FIGURE 10–11 Typical drum brake shoe and             ...
DRUM BRAKE SHOES        PRIMARY AND SECONDARY BRAKE SHOES   •      In a dual-servo drum brake system, the shoes in a      ...
DRUM BRAKE SHOES        PRIMARY AND SECONDARY BRAKE SHOES        FIGURE 10–12 The primary (forward facing)             FIG...
DRUM BRAKE SHOES        LINING ASSEMBLY METHODS   •      There are two main          methods used to mount          brake ...
DRUM BRAKE SHOES        LINING ASSEMBLY METHODS                                FIGURE 10–15 Many brake linings are bonded....
DRUM BRAKE SHOES        EDGE CODES   •      Starting in 1964, brake linings have been using a          standardized way to...
DRUM BRAKE SHOES        EDGE CODESAutomotive Brake Systems, 5/e        Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Ed...
DRUM BRAKE SHOES        EDGE CODES                                FIGURE 10–16 Typical drum brake lining edge codes.Automo...
Purchase Quality Brake Linings for Best        Performance          •     While many brands of replacement brake          ...
DRUM BRAKE PARTS        RETURN SPRINGS   •      The brake shoe return          springs retract the shoes          to their...
DRUM BRAKE PARTS        RETURN SPRINGS                          FIGURE 10–18 A single spring-steel spring is used on some ...
DRUM BRAKE PARTS        BRAKE SHOE HOLDDOWNS   •      While the return springs retract the brake shoes to          their u...
DRUM BRAKE PARTS        BRAKE SHOE HOLDDOWNS                                FIGURE 10–19 Various types and styles of hold-...
DRUM BRAKE PARTS        PARKING BRAKE LINKAGE   •      Most rear drum brake          friction assemblies include          ...
DRUM BRAKE PARTS        BRAKE DRUMS   •      The brake drum is not          connected to the backing          plate, but t...
NON-SERVO BRAKE DESIGN        PURPOSE AND FUNCTION   •      A non-servo brake feature is that each brake          shoe is ...
NON-SERVO BRAKE DESIGN        PARTS AND OPERATION   •      Self-energizing action occurs when the forward or          lead...
NON-SERVO BRAKE DESIGN        PARTS AND OPERATION                                           FIGURE 10–22 Self-            ...
NON-SERVO BRAKE DESIGN        DOUBLE-TRAILING BRAKE   •      The least powerful non-          servo drum brake is the     ...
NON-SERVO BRAKE DESIGN        LEADING-TRAILING BRAKE DESIGN   •      The non-servo leading-          trailing brake has on...
DUAL-SERVO BRAKE DESIGN        PURPOSE AND FUNCTION   •      The dual-servo brake is the most common drum brake          d...
DUAL-SERVO BRAKE DESIGN        DUAL-SERVO BRAKE CONSTRUCTION   •      The basic dual-servo brake          uses one anchor ...
DUAL-SERVO BRAKE DESIGN        DUAL-SERVO BRAKE CONSTRUCTION                                FIGURE 10–26 A typical dual-se...
DUAL-SERVO BRAKE DESIGN        DUAL-SERVO BRAKE OPERATION   •      When a dual-servo brake is          applied, the wheel ...
DUAL-SERVO BRAKE DESIGN        SERVO ACTION   •      Once all clearance is taken up between the brake          shoes, adju...
DUAL-SERVO BRAKE DESIGN        SERVO ACTION                                     FIGURE 10–28 Dual servo action greatly    ...
Rear Wheel Lockup? Check the        Adjustment          •     Servo action enables a drum brake to provide                ...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS   •      Servo brakes use three styles of starw...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS                                FIGURE 10–29 A c...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS                                FIGURE 10–30 A l...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS                       FIGURE 10–31 A link-actua...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS                                       FIGURE 10...
AUTOMATIC BRAKE ADJUSTERS        SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS                                       FIGURE 10...
AUTOMATIC BRAKE ADJUSTERS        NON-SERVO STARWHEEL AUTOMATIC ADJUSTERS   •      OPERATION.            •    The starwheel...
AUTOMATIC BRAKE ADJUSTERS        NON-SERVO STARWHEEL AUTOMATIC ADJUSTERS                                         FIGURE 10...
AUTOMATIC BRAKE ADJUSTERS        RATCHET-TYPE AUTOMATIC ADJUSTERS   •      Most ratchet automatic adjusters use movement o...
AUTOMATIC BRAKE ADJUSTERS        RATCHET-TYPE AUTOMATIC ADJUSTERS   •      LEVER-LATCH RATCHET AUTOMATIC          ADJUSTER...
AUTOMATIC BRAKE ADJUSTERS        RATCHET-TYPE AUTOMATIC ADJUSTERS                                FIGURE 10–36 A lever-latc...
AUTOMATIC BRAKE ADJUSTERS        RATCHET-TYPE AUTOMATIC ADJUSTERS                                      FIGURE 10–37 A stru...
Cool the Brakes before Backing          •     Self-adjusters can over-adjust the rear drum brakes if                the br...
SUMMARY   1.       Drum brake shoes include the lining table and shoe web            plus holes for the springs to attach ...
SUMMARY   6.       Dual-servo brakes use primary and secondary brake            shoes that are connected at one end. The w...
REVIEW QUESTIONS   1.        Describe the difference between a dual-servo and             a leading–trailing drum brake sy...
CHAPTER QUIZ   1. Two technicians are discussing drum brake      shoes. Technician A says that forward and      rearward f...
CHAPTER QUIZ   2. Two technicians are discussing brake lining edge      codes. Technician A says that the code can      id...
CHAPTER QUIZ   3. Technician A says that starwheel adjusters use      different threads (left- and right-handed) for the  ...
CHAPTER QUIZ   4. Technician A says that drum brakes can fail to      slow the vehicle if driven through deep water.      ...
CHAPTER QUIZ   5.                                Technician A says                                     that self-adjusters...
CHAPTER QUIZ   6. Drum brake shoes ________.            a.       Can have riveted linings            b.       Can have bon...
CHAPTER QUIZ   7. Which lining does most of the braking on a dual-      servo brake?            a.       Front (forward fa...
CHAPTER QUIZ   8. Which lining does most of the braking on a      leading-trailing brake?            a.       Leading (for...
CHAPTER QUIZ   9. Two technicians are discussing drum brake self-      adjusters. Technician A says that a frozen      sta...
CHAPTER QUIZ   10.A typical drum brake backing plate has how many      shoe support pads (also called ledges)?            ...
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Transcript of "Brakesdrumchapter10 111221140048-phpapp01 (1)"

  1. 1. CHAPTER 10Drum Brakes
  2. 2. OBJECTIVES After studying Chapter 10, the reader will be able to: 1. Prepare for the Brakes (A5) ASE certification test content area “B” (Drum Brake Diagnosis and Repair). 2. Identify drum brake component parts. 3. Describe the operation of non-servo brakes. 4. Explain the operation of dual-servo brakes. 5. Discuss drum brake adjusters.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 2 Upper Saddle River, NJ 07458 • All rights reserved.
  3. 3. KEY TERMS • Anchor eyes • Lining fade • Beehive holddown • Lining table • Bonded linings • Mechanical fade • Brake fade • Nibs • Brake shoe return springs • Non-servo brakes • Brake shoe holddown • Over-travel spring • Brake shoes • Pawl • Core charge • Piston stops • Double-trailing shoe • Platform • Dual-servo brake • Primary shoe • Duo-Servo • Riveted linings • Edge codes • Secondary shoe • Gas fade • Self-energizing action • Labyrinth seal • Shoe anchors • Leading shoe • Shoe contact areas • Leading-trailing brakes • Shoe rim • Ledges • Shoe support pads • Lining edge codes • Shoe web • Trailing shoe • Water fadeAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 3 Upper Saddle River, NJ 07458 • All rights reserved.
  4. 4. DRUM BRAKE ADVANTAGES • Drum brakes were the first type of brakes used on motor vehicles. • Even today, over 100 years after the first “horseless carriages,” drum brakes are still used on the rear of most vehicles.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 4 Upper Saddle River, NJ 07458 • All rights reserved.
  5. 5. DRUM BRAKE ADVANTAGES FIGURE 10–1 Typical brake system components showing disc brakes on the front and drum brakes on the rear.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 5 Upper Saddle River, NJ 07458 • All rights reserved.
  6. 6. DRUM BRAKE ADVANTAGES FIGURE 10–2 An exploded view of a typical drum brake assembly.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 6 Upper Saddle River, NJ 07458 • All rights reserved.
  7. 7. DRUM BRAKE ADVANTAGES • SELF-ENERGIZING AND SERVO ACTION • PARKING BRAKE SERVICEAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 7 Upper Saddle River, NJ 07458 • All rights reserved.
  8. 8. DRUM BRAKE DISADVANTAGES BRAKE FADE • Drum brakes are not very efficient at dissipating heat. • The brake drum covers the linings, and most of the heat produced during braking must pass through the drum, from the inside out into the air. • The greatest drawback of drum brakes is that they are susceptible to fade. • Brake fade is the loss of stopping power that occurs when excessive heat reduces the friction between the brake shoe linings and the drum.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 8 Upper Saddle River, NJ 07458 • All rights reserved.
  9. 9. DRUM BRAKE DISADVANTAGES BRAKE FADE • The four types of brake fade include: • 1. Mechanical Fade • 2. Lining Fade • 3. Gas Fade • 4. Water FadeAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 9 Upper Saddle River, NJ 07458 • All rights reserved.
  10. 10. DRUM BRAKE DISADVANTAGES • BRAKE ADJUSTMENT • BRAKE PULLAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 10 Upper Saddle River, NJ 07458 • All rights reserved.
  11. 11. Quick-and-Easy Drum Brake Adjustment Check • Tap the brake drum lightly with a hammer or wrench. If the brake shoes are not contacting the drum, the drum will ring like a bell. If the shoes are contacting the drum, the sound will be muffled.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 11 Upper Saddle River, NJ 07458 • All rights reserved.
  12. 12. DRUM BRAKE PARTS BACKING PLATE • The foundation of every drum brake is the backing plate that mounts to the steering knuckle on the front brakes, or to the suspension or axle housing on the rear brakes. FIGURE 10–3 The backing plate is the foundation of every drum brake.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 12 Upper Saddle River, NJ 07458 • All rights reserved.
  13. 13. DRUM BRAKE PARTS BACKING PLATE FIGURE 10–4 A labyrinth seal is created between the lip of the backing plate and the groove in the brake drum.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 13 Upper Saddle River, NJ 07458 • All rights reserved.
  14. 14. DRUM BRAKE PARTS SHOE ANCHORS • Shoe anchors prevent the brake shoes from rotating with the drum when the brakes are applied. • The majority of drum brakes have a single anchor, but some drum brake designs use two or more. FIGURE 10–5 A keystone anchor allows the brake shoes to self-center in the drum.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 14 Upper Saddle River, NJ 07458 • All rights reserved.
  15. 15. DRUM BRAKE PARTS PISTON STOPS • Some backing plates incorporate piston stops that prevent the wheel cylinder pistons from coming out of their bores when the friction assembly is disassembled for servicing. FIGURE 10–6 Piston stops prevent the wheel cylinder from coming apart.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 15 Upper Saddle River, NJ 07458 • All rights reserved.
  16. 16. DRUM BRAKE PARTS SHOE SUPPORT PADS • The shoe support pads are stamped into the backing plate and contact the edges of the brake shoes to keep the linings properly aligned with the center of the friction surface inside the brake drum. • These pads are also called ledges or shoe contact areas. • The support pads are slightly coated with special high-temperature silicone brake grease to minimize wear, prevent rust, and eliminate squeaking that can occur when the shoes move slightly on the pads during a stop.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 16 Upper Saddle River, NJ 07458 • All rights reserved.
  17. 17. DRUM BRAKE PARTS WHEEL CYLINDERS • Hydraulic pressure is transferred from the master cylinder to each wheel cylinder through brake fluid. • The force exerted on the brake fluid by the driver forces the piston inside the wheel cylinder to move outward. FIGURE 10–7 Cross-section of a wheel cylinder that shows all of its internal parts. The brake line attaches to the fluid inlet. The cup extender prevents the cup seal lip from collapsing when the brakes are released.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 17 Upper Saddle River, NJ 07458 • All rights reserved.
  18. 18. DRUM BRAKE PARTS WHEEL CYLINDERS FIGURE 10–8 The pushrods are held in place by the rubber dust boots. As the wheel cylinder pistons move outward, the pushrods transfer the movement to the brake shoes.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 18 Upper Saddle River, NJ 07458 • All rights reserved.
  19. 19. DRUM BRAKE SHOES • The linings of drum brakes are attached to curved metal assemblies called brake shoes. • Most shoes are made of two pieces of sheet steel welded together in a T- shaped cross section. FIGURE 10–9 Steelbrake shoes are made from two stampings welded together—the web and the lining table.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 19 Upper Saddle River, NJ 07458 • All rights reserved.
  20. 20. DRUM BRAKE SHOES FIGURE 10–11 Typical drum brake shoe and the names of the parts. (Courtesy of Allied Signal Automotive Aftermarket) FIGURE 10–10 Tapered ends on the linings help to reduce brake noise.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 20 Upper Saddle River, NJ 07458 • All rights reserved.
  21. 21. DRUM BRAKE SHOES PRIMARY AND SECONDARY BRAKE SHOES • In a dual-servo drum brake system, the shoes in a dual-servo brake perform different jobs. • The primary shoe (forward facing shoe) is self- energized by drum rotation to create a servo action that forces the secondary shoe more firmly against the drum. • Because of this, the two shoes have physical differences and cannot be interchanged.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 21 Upper Saddle River, NJ 07458 • All rights reserved.
  22. 22. DRUM BRAKE SHOES PRIMARY AND SECONDARY BRAKE SHOES FIGURE 10–12 The primary (forward facing) FIGURE 10–13 Primary shoe lining may brake shoe often has a shorter lining than the vary depending on the application. secondary shoe (rearward facing).Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 22 Upper Saddle River, NJ 07458 • All rights reserved.
  23. 23. DRUM BRAKE SHOES LINING ASSEMBLY METHODS • There are two main methods used to mount brake linings to the brake shoe. • RIVETING • BONDING FIGURE 10–14 Riveted brake linings are quiet and reliable at high temperatures.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 23 Upper Saddle River, NJ 07458 • All rights reserved.
  24. 24. DRUM BRAKE SHOES LINING ASSEMBLY METHODS FIGURE 10–15 Many brake linings are bonded.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 24 Upper Saddle River, NJ 07458 • All rights reserved.
  25. 25. DRUM BRAKE SHOES EDGE CODES • Starting in 1964, brake linings have been using a standardized way to identify the brake lining materials. • The edge codes follow the Society of Automotive Engineers (SAE) Standard J866a. • The edge codes contain three groups of letters and numbers: • The first group is a series of letters that identify the manufacturer of the lining. • The second group is a series of numbers, letters, or both that identify the lining compound or formula. • The third group is two letters that identify the coefficient of friction.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 25 Upper Saddle River, NJ 07458 • All rights reserved.
  26. 26. DRUM BRAKE SHOES EDGE CODESAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 26 Upper Saddle River, NJ 07458 • All rights reserved.
  27. 27. DRUM BRAKE SHOES EDGE CODES FIGURE 10–16 Typical drum brake lining edge codes.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 27 Upper Saddle River, NJ 07458 • All rights reserved.
  28. 28. Purchase Quality Brake Linings for Best Performance • While many brands of replacement brake lining provide acceptable stopping power and long life, purchasing factory brake lining from a dealer is usually the best opportunity to get lining material that meets all vehicle requirements. Aftermarket linings are not required by federal law to meet performance or wear standards that are required of original factory brake linings.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 28 Upper Saddle River, NJ 07458 • All rights reserved.
  29. 29. DRUM BRAKE PARTS RETURN SPRINGS • The brake shoe return springs retract the shoes to their unapplied positions when the brake pedal is released. • This helps prevent brake drag, and aids the return of brake fluid to the master cylinder reservoir. • Most brakes use closed- coil return springs to retract the brake shoes. FIGURE 10–17 A typical drum brake assembly showing the support plate (backing plate), anchor pin, and springs.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 29 Upper Saddle River, NJ 07458 • All rights reserved.
  30. 30. DRUM BRAKE PARTS RETURN SPRINGS FIGURE 10–18 A single spring-steel spring is used on some drum brakes.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 30 Upper Saddle River, NJ 07458 • All rights reserved.
  31. 31. DRUM BRAKE PARTS BRAKE SHOE HOLDDOWNS • While the return springs retract the brake shoes to their unapplied positions, the brake shoe holddowns keep the shoes securely against the support pads on the backing plate. • The holddowns prevent noise, vibration, and wear, but still allow the shoes to move out and back as the brakes are applied and released. • The holddowns also provide enough freedom of movement to allow adjustments of the shoes outward as the linings wear.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 31 Upper Saddle River, NJ 07458 • All rights reserved.
  32. 32. DRUM BRAKE PARTS BRAKE SHOE HOLDDOWNS FIGURE 10–19 Various types and styles of hold-down springs.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 32 Upper Saddle River, NJ 07458 • All rights reserved.
  33. 33. DRUM BRAKE PARTS PARKING BRAKE LINKAGE • Most rear drum brake friction assemblies include a parking brake linkage. • The linkage commonly consists of a cable, lever, and strut system that spread the brake shoes apart to apply the brake mechanically. • The parking brake strut plays a large part in many of the automatic brake adjusters. FIGURE 10–20 A mechanical brake linkage is part of most drum brake assemblies.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 33 Upper Saddle River, NJ 07458 • All rights reserved.
  34. 34. DRUM BRAKE PARTS BRAKE DRUMS • The brake drum is not connected to the backing plate, but turns with the wheel. • The drum mounts on the hub or axle, and covers the rest of the brake assembly. • Brake drums are made of cast iron or cast aluminum with a castiron liner. • Many of these drum types may have ribs or fins on FIGURE 10–21 An aluminium brake drum with their outer edge to help a cast iron friction surface. The cooling fins around the outside help dissipate the heat from dissipate heat. the friction surface to the outside air.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 34 Upper Saddle River, NJ 07458 • All rights reserved.
  35. 35. NON-SERVO BRAKE DESIGN PURPOSE AND FUNCTION • A non-servo brake feature is that each brake shoe is applied individually. • The action of one shoe has no effect on the action of the other. • Many non-servo drum brakes use self-energizing action to improve their braking performance.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 35 Upper Saddle River, NJ 07458 • All rights reserved.
  36. 36. NON-SERVO BRAKE DESIGN PARTS AND OPERATION • Self-energizing action occurs when the forward or leading shoe contacts the drum and the drum attempts to rotate the shoe along with it. • However, the shoe cannot rotate because its far end (relative to drum rotation) is fixed in place by an anchor. • As a result, drum rotation energizes the shoe by forcing it outward and wedging it tightly against the brake drum.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 36 Upper Saddle River, NJ 07458 • All rights reserved.
  37. 37. NON-SERVO BRAKE DESIGN PARTS AND OPERATION FIGURE 10–22 Self- energizing action can increase or decrease the stopping power of a brake shoe.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 37 Upper Saddle River, NJ 07458 • All rights reserved.
  38. 38. NON-SERVO BRAKE DESIGN DOUBLE-TRAILING BRAKE • The least powerful non- servo drum brake is the double-trailing brake. FIGURE 10–23 A double-trailing non-servo drum brake.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 38 Upper Saddle River, NJ 07458 • All rights reserved.
  39. 39. NON-SERVO BRAKE DESIGN LEADING-TRAILING BRAKE DESIGN • The non-servo leading- trailing brake has one leading shoe and one trailing shoe. FIGURE 10–24 A leading-trailing non-servo brake.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 39 Upper Saddle River, NJ 07458 • All rights reserved.
  40. 40. DUAL-SERVO BRAKE DESIGN PURPOSE AND FUNCTION • The dual-servo brake is the most common drum brake design. • The name “servo” comes from the fact that one shoe “serves” the other to increase application force. • All servo brakes used on automobiles are of the dual-servo design that works with equal force in both directions. • The primary advantage of the dual-servo brake is that it is more powerful than any of the non-servo designs. • Another advantage of the dual-servo brake is that it makes a good parking brake. • Dual-servo action not only makes the brake very powerful, it allows the brake to hold equally well in both directions.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 40 Upper Saddle River, NJ 07458 • All rights reserved.
  41. 41. DUAL-SERVO BRAKE DESIGN DUAL-SERVO BRAKE CONSTRUCTION • The basic dual-servo brake uses one anchor and a single two-piston wheel cylinder. • ADJUSTING LINK • PRIMARY AND SECONDARY BRAKE SHOES FIGURE 10–25 A typical dual-servo drum brake.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 41 Upper Saddle River, NJ 07458 • All rights reserved.
  42. 42. DUAL-SERVO BRAKE DESIGN DUAL-SERVO BRAKE CONSTRUCTION FIGURE 10–26 A typical dual-servo brake adjusting link assembly.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 42 Upper Saddle River, NJ 07458 • All rights reserved.
  43. 43. DUAL-SERVO BRAKE DESIGN DUAL-SERVO BRAKE OPERATION • When a dual-servo brake is applied, the wheel cylinder attempts to force the tops of both brake shoes outward against the drum. FIGURE 10–27 Dual-servo brake operation. The primary shoe on the left exerts a force on the secondary shoe on the right.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 43 Upper Saddle River, NJ 07458 • All rights reserved.
  44. 44. DUAL-SERVO BRAKE DESIGN SERVO ACTION • Once all clearance is taken up between the brake shoes, adjusting link, and anchor, both brake shoes become self-energized like the leading shoes in a non-servo brake. • The anchor pin prevents the secondary shoe from rotating, and the adjusting link (held in position by the secondary shoe) serves as the anchor for the primary shoe. • Servo action then occurs as a part of the braking force generated by the primary shoe is transferred through the adjusting link to help apply the secondary shoe.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 44 Upper Saddle River, NJ 07458 • All rights reserved.
  45. 45. DUAL-SERVO BRAKE DESIGN SERVO ACTION FIGURE 10–28 Dual servo action greatly increases the application force on the secondary shoe.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 45 Upper Saddle River, NJ 07458 • All rights reserved.
  46. 46. Rear Wheel Lockup? Check the Adjustment • Servo action enables a drum brake to provide increased stopping power, but it can also cause the brakes to grab and lock if they get too far out of adjustment. As clearance between the shoes and drum increases, the primary brake shoe is allowed a greater range of movement. The farther the shoe moves, the more speed it picks up from the rotating brake drum. At the moment the slack is taken up between the brake shoes, adjusting link, and anchor, the speed of the primary shoe is converted into application force by servo action. If the primary shoe is moving too quickly, it will apply the secondary shoe very hard and fast, causing the brakes to grab and possibly lock the wheels.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 46 Upper Saddle River, NJ 07458 • All rights reserved.
  47. 47. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS • Servo brakes use three styles of starwheel adjusters: • Cable • Lever • LinkAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 47 Upper Saddle River, NJ 07458 • All rights reserved.
  48. 48. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–29 A cable-actuated starwheel adjuster. This type of adjuster makes the adjustment as the brakes are released.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 48 Upper Saddle River, NJ 07458 • All rights reserved.
  49. 49. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–30 A lever-actuated starwheel automatic adjuster. This type of adjuster makes the adjustment when the brakes are applied.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 49 Upper Saddle River, NJ 07458 • All rights reserved.
  50. 50. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–31 A link-actuated starwheel adjuster. This type of adjuster makes the adjustment when the brakes are released.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 50 Upper Saddle River, NJ 07458 • All rights reserved.
  51. 51. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–32 The operation of a typical self-adjuster. Notice that the adjuster actually moves the starwheel.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 51 Upper Saddle River, NJ 07458 • All rights reserved.
  52. 52. AUTOMATIC BRAKE ADJUSTERS SERVO BRAKE STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–33 A cable-actuated starwheel adjuster with an over-travel spring.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 52 Upper Saddle River, NJ 07458 • All rights reserved.
  53. 53. AUTOMATIC BRAKE ADJUSTERS NON-SERVO STARWHEEL AUTOMATIC ADJUSTERS • OPERATION. • The starwheel automatic adjusters used on nonservo brakes may be mounted on either the leading or trailing shoe. • These types of adjusters work whenever the brakes are applied—in either the forward or reverse direction. FIGURE 10–34 A non-servo brake with a lever-actuated starwheel automatic adjuster on a leading shoe. This type of adjuster makes an adjustment as the brakes are applied.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 53 Upper Saddle River, NJ 07458 • All rights reserved.
  54. 54. AUTOMATIC BRAKE ADJUSTERS NON-SERVO STARWHEEL AUTOMATIC ADJUSTERS FIGURE 10–35 A non-servo brake with a lever-actuated starwheel automatic adjuster on the trailing shoe. This type of adjuster makes the adjustment as the brakes are released.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 54 Upper Saddle River, NJ 07458 • All rights reserved.
  55. 55. AUTOMATIC BRAKE ADJUSTERS RATCHET-TYPE AUTOMATIC ADJUSTERS • Most ratchet automatic adjusters use movement of the brake shoes to adjust the lining-to-drum clearance. • The adjustment of a ratchet adjuster is carried out by two parts that have small interlocking teeth. • As the adjustment is made, the two toothed elements ratchet across one another. • Once adjustment is complete, the teeth lock together to hold the brake shoes in their new positions.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 55 Upper Saddle River, NJ 07458 • All rights reserved.
  56. 56. AUTOMATIC BRAKE ADJUSTERS RATCHET-TYPE AUTOMATIC ADJUSTERS • LEVER-LATCH RATCHET AUTOMATIC ADJUSTER • STRUT-QUADRANT RATCHET AUTOMATIC ADJUSTERAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 56 Upper Saddle River, NJ 07458 • All rights reserved.
  57. 57. AUTOMATIC BRAKE ADJUSTERS RATCHET-TYPE AUTOMATIC ADJUSTERS FIGURE 10–36 A lever-latch ratchet automatic adjuster.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 57 Upper Saddle River, NJ 07458 • All rights reserved.
  58. 58. AUTOMATIC BRAKE ADJUSTERS RATCHET-TYPE AUTOMATIC ADJUSTERS FIGURE 10–37 A strut-quadrant ratchet automatic adjuster.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 58 Upper Saddle River, NJ 07458 • All rights reserved.
  59. 59. Cool the Brakes before Backing • Self-adjusters can over-adjust the rear drum brakes if the brake drums are hot and have increased in diameter due to the heat. For example, if a pickup truck towing a boat had to brake while backing down a long, steep grade to the boat ramp, the rear brake drums could become larger in diameter due to the heat created during braking. The brakes could overadjust if the driver repeatedly depresses and releases the brake pedal while backing the trailer down the boat ramp. Then, after the boat has been removed from the trailer and the rear brakes have cooled, the drums will shrink and keep the rear brakes from releasing, preventing the truck from moving up the ramp.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 59 Upper Saddle River, NJ 07458 • All rights reserved.
  60. 60. SUMMARY 1. Drum brake shoes include the lining table and shoe web plus holes for the springs to attach and semicircular anchor eyes. 2. Brake linings can be attached using rivets or bonding. 3. Lining edge codes identify the manufacturer and include two letters at the end, which identify the coefficient of friction of the material. The first letter indicates the coefficient when the lining is cold and the second indicates the coefficient when the lining is hot. 4. Brake shoes are forced outward against a brake drum by hydraulic action working on the brake shoes by the piston of a wheel cylinder. 5. The curved arch of the brake shoe causes a wedging action between the brake shoe and the rotating drum. This wedging action increases the amount of force applied to the drum.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 60 Upper Saddle River, NJ 07458 • All rights reserved.
  61. 61. SUMMARY 6. Dual-servo brakes use primary and secondary brake shoes that are connected at one end. The wedge action on the front (primary) shoe forces the secondary shoe into the drum with even greater force. This action is called servo self-energizing. 7. Leading-trailing brakes use two brake shoes that are not connected. Leading-trailing brakes operate on a more linear basis and are therefore more suited than dual-servo for ABS. 8. Most self-adjusting mechanisms usually operate from the secondary or rearward facing brake shoe and adjust the brakes as the brakes are released. 9. Some self-adjusters operate on the primary shoe and adjust the brakes as they are being applied.Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 61 Upper Saddle River, NJ 07458 • All rights reserved.
  62. 62. REVIEW QUESTIONS 1. Describe the difference between a dual-servo and a leading–trailing drum brake system. 2. List all the parts of a typical drum brake. 3. Explain how a self-adjusting brake mechanism works. 4. What do the last two letters of the lining or pad edge code identify?Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 62 Upper Saddle River, NJ 07458 • All rights reserved.
  63. 63. CHAPTER QUIZ 1. Two technicians are discussing drum brake shoes. Technician A says that forward and rearward facing shoes are the same and can be installed in either position on any drum brake system. Technician B says that the darker color lining should always be placed toward the front of the vehicle. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor BAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 63 Upper Saddle River, NJ 07458 • All rights reserved.
  64. 64. CHAPTER QUIZ 2. Two technicians are discussing brake lining edge codes. Technician A says that the code can identify the manufacturer. Technician B says that all friction material from the same manufacturer will have the same edge codes. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor BAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 64 Upper Saddle River, NJ 07458 • All rights reserved.
  65. 65. CHAPTER QUIZ 3. Technician A says that starwheel adjusters use different threads (left- and right-handed) for the left and right sides of the vehicle. Technician B says that a pawl controls the teeth of the starwheel adjuster. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor BAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 65 Upper Saddle River, NJ 07458 • All rights reserved.
  66. 66. CHAPTER QUIZ 4. Technician A says that drum brakes can fail to slow the vehicle if driven through deep water. Technician B says that when drum brakes get hot, the brake pedal will drop because the drum expands away from the shoes. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor BAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 66 Upper Saddle River, NJ 07458 • All rights reserved.
  67. 67. CHAPTER QUIZ 5. Technician A says that self-adjusters used on most drum brakes work when the brakes are applied, then release while traveling in reverse. Technician B says that some adjusters can overadjust if the brake drums are hot. Which technician is correct? Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,Automotive Brake Systems, 5/eBy James D. Halderman 67 Upper Saddle River, NJ 07458 • All rights reserved.
  68. 68. CHAPTER QUIZ 6. Drum brake shoes ________. a. Can have riveted linings b. Can have bonded linings c. Can have one shoe that is longer than the other on the same wheel brake d. All of the above are possibleAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 68 Upper Saddle River, NJ 07458 • All rights reserved.
  69. 69. CHAPTER QUIZ 7. Which lining does most of the braking on a dual- servo brake? a. Front (forward facing) b. Rear (rearward facing) c. Both contribute equally d. Depends on the speed of the vehicleAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 69 Upper Saddle River, NJ 07458 • All rights reserved.
  70. 70. CHAPTER QUIZ 8. Which lining does most of the braking on a leading-trailing brake? a. Leading (forward facing) b. Trailing (rearward facing) c. Both contribute equally d. Depends on the speed of the vehicleAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 70 Upper Saddle River, NJ 07458 • All rights reserved.
  71. 71. CHAPTER QUIZ 9. Two technicians are discussing drum brake self- adjusters. Technician A says that a frozen starwheel adjuster can cause the brakes to lock up due to the adjusting lever being unable to move the adjuster causing the linkage to bind. Technician B says that some brakes self-adjust when the brakes are applied rather than when released. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor BAutomotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 71 Upper Saddle River, NJ 07458 • All rights reserved.
  72. 72. CHAPTER QUIZ 10.A typical drum brake backing plate has how many shoe support pads (also called ledges)? a. 3 b. 4 c. 6 d. 8Automotive Brake Systems, 5/e Copyright © 2010, 2008, 2004, 2000, 1995 Pearson Education, Inc.,By James D. Halderman 72 Upper Saddle River, NJ 07458 • All rights reserved.
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