<ul><li>Prepare for the ASE Manual Drive Train and Axles (A3) certification test content area “B” (Transmission Diagnosis and Repair) and content area “C” (Transaxle Diagnosis and Repair). </li></ul><ul><li>Explain how to calculate gear ratios. </li></ul><ul><li>Name the parts of a typical manually shifted transmission/transaxle. </li></ul>OBJECTIVES: After studying Chapter 95, the reader should be able to: Continued
<ul><li>Describe how the synchronizer assembly allows for smooth, clash-free shifting. </li></ul><ul><li>Describe the different types of lubricants that may be used in a manual transmission/transaxle. </li></ul><ul><li>Diagnose a difficult-to-shift manual transmission/transaxle. </li></ul>OBJECTIVES: After studying Chapter 95, the reader should be able to:
<ul><li>axis back taper • bell housing • bevel gear • blocker ring cluster gears • cluster shaft • cluster gear • constant-mesh gear • counter gears • countershaft direct drive • drive gear • driven gear extension housing • external gears fifth gear • final drive assembly • first gear • fourth gear • front bearing retainers </li></ul>KEY TERMS: Continued
<ul><li>gear reduction helical gear • hypoid gear set input shaft • internal ring gears keys lay shaft main drive pinion assembly • main gear • main shaft neutral </li></ul>KEY TERMS: Continued
<ul><li>output shaft • overdrive pinion gear quill reverse second gear • sliding reverse gear • sliding sleeve • springs • spur gear • stop ring • synchronizer assemblies • synchronizer ring third gear • transmission case </li></ul>KEY TERMS:
THE NEED FOR A TRANSMISSION <ul><li>A vehicle requires a lot of torque to start off and to climb hills, yet it does not require as much torque to move on level ground. Torque is a twisting or turning force that is exerted on the input shaft of a transmission/transaxle. An engine produces increasing torque as its speed increases up to a certain point where the torque output starts to decrease. To get a vehicle moving or to accelerate up a hill, it is desirable to use a transmission that allows the engine speed to be increased even though the vehicle speed may be low. Using gears allows the engine speed to increase at low vehicle speeds yet still permits it to drop at higher speeds to save fuel and reduce emissions. </li></ul>Continued
<ul><li>A transmission is used on rear-wheel-drive vehicles, whereas a transaxle is usually used on front-wheel-drive vehicles. A vehicle equipped with a transmission uses a separate differential to split the torque equally to the drive wheels.A transaxle includes a differential assembly. In a transaxle, the differential, sometimes called the final drive unit , is incorporated in the construction of the transmission. </li></ul>First gear : Vehicle speed is low , engine speed is high . Second gear : Vehicle speed increases , engine speed decrease . Third gear : Vehicle speed continues to increase , engine speed is kept in a narrow range. Fourth gear : Again, the vehicle speed is increasing , yet engine speed is about the same as in third gear. What Is the Difference Between a Transmission and a Transaxle?
GEAR TYPES <ul><li>The simplest type of gear is the spur gear , consisting of a gear blank with straight-cut teeth around its entire circumference. All gear teeth lie parallel to the centerline, or axis , of the gear. The teeth are shaped so they can mesh without slippage with a second spur gear’s teeth positioned along a parallel axis. </li></ul>Figure 95–1 Spur gears have straight-cut teeth. Continued
<ul><li>A helical gear , although similar to a spur gear, has its teeth cut at an angle to the axis of the gear. This enables more teeth, 2.5 to 3.5, to mesh at a time than the spur gear. The angle allows the teeth to mesh gradually, rather than all at once. As a result, helical gears run quieter than spur gears. Helical gears have two disadvantages. Each gear pushes against its shaft parallel to its axis. Special bearings are needed to protect the gearbox from this type of axial, or thrust, loading. </li></ul><ul><li>Because of the increased contact area, helical gears create more friction than spur gears. See Figures 95–2 and 95–3. </li></ul>Continued
Figure 95–3 A spur gear has straight-cut teeth. This design is very strong and is used where strength is important. Spur gears are noisy during operation. Helical-cut gears, on the other hand, operate quietly but create a force in line with the axis of the gears due to the angle of the gear teeth. Figure 95–2 The teeth of a helical gear are cut at an angle to the gear axis. Continued
<ul><li>Spur and helical gears have teeth on their outside circumference and, for this reason, are called external gears . This type of gear is the most commonly used in manual transmissions and transaxles. Gears having teeth along the inside circumference are called internal ring gears . The teeth of an internal ring gear may be spur or helical teeth. An internal ring gear may mesh with a smaller external gear designed to rotate as it travels around the inside of the internal ring gear. This type of external gear is called a pinion gear because of its smaller diameter. See Figure 95–4. </li></ul>Continued
Figure 95–4 A pinion gear meshed with an internal ring gear rotates in the same direction around a parallel axis of rotation. Continued
<ul><li>When an external gear meshes with an internal ring gear, both gears rotate in the same direction, but when an external gear meshes with another external gear, the gears rotate in opposite directions as shown here. </li></ul>Figure 95–5 When two external gears mesh, they rotate in opposite directions. Continued
Figure 95–6 Bevel gears are often used to change the direction of rotation and are typically used in differentials. <ul><li>Bevel Gears The teeth of a bevel gear are cut at an angle to the outside gear surface. Simple bevel gears have straight-cut teeth similar to those on a spur gear. Special gears used in a differential, called spider gears, are a common example of the simple bevel gear. </li></ul>Continued
<ul><li>Hypoid Gears Hypoid gear sets have gear teeth that are curved much like the teeth of a spiral bevel gear. The pinion gear is offset below the centerline of the ring gear. This design provides maximum gear tooth contact for strength, gradual tooth engagement, and quiet operation. Hypoid gears are generally available only as a matched set. Hypoid gears are commonly used as the final drive gears in rear axles where load-carrying ability and low noise are important. The offset pinion allows the driveshaft to be positioned lower in the vehicle, reducing the size of the hump in the vehicle’s interior. See Figure 95–7. </li></ul>Continued
Figure 95–7 A differential uses a hypoid gear set to provide a change in the direction of torque and for gear reduction (torque increases) to the drive wheels. Continued
GEAR RATIOS <ul><li>When one gear turns another, the speed that the two gears turn in relation to each other is the gear ratio. Gear ratio is expressed as the number of rotations the drive gear must make in order to rotate the driven gear through one revolution. To obtain a gear ratio, divide the number of teeth on the driven gear by the number of teeth on the drive gear. </li></ul>Continued <ul><li>Direct drive </li></ul><ul><li>Gear reduction </li></ul><ul><li>Overdrive </li></ul>Gear ratios, expressed relative to the number one, fall into three categories:
<ul><li>Direct Drive If two meshed gears are the same size and have the same number of teeth, they will turn at the same speed. Since the drive gear turns once for each revolution of the driven gear, the gear ratio is 1:1; this is called a direct drive . When a transmission is in direct drive, the engine and transmission turn at the same speed. </li></ul>Continued NOTE: Ratios always end in one with a colon in between. Therefore, the first number is less than one if it is an overdrive ratio and greater than one if it is a gear reduction ratio.
<ul><li>Gear Reduction If one gear drives a second gear that has three times the number of teeth, the smaller drive gear must travel three complete revolutions in order to drive the larger gear through one rotation. Divide the number of teeth on the driven gear by the number of teeth on the drive gear and you get a 3:1 gear ratio (pronounced three to one). This type of gear arrangement, where driven gear speed is slower than drive gear speed, provides gear reduction . Gear reduction may also be called underdrive as drive speed is less than, or under, driven speed and is used for the lower gears in a transmission. </li></ul>Continued
<ul><li>First gear in a transmission is called “low” gear because output speed, not gear ratio, is low. Low gears have numerically high gear ratios. A 3:1 gear ratio is a lower gear than those with a 2:1 or 1:1 gear ratio. </li></ul>Figure 95–8 This gear combination provides a gear reduction of 3:1. Continued These three ratios taken in order represent a typical upshift pattern from low gear (3:1), to second gear (2:1), to drive gear (1:1).
<ul><li>Overdrive The opposite of a gear reduction is called Overdrive and occurs when a driven gear turns faster than its drive gear. For the gears shown here, the driven gear turns three times for each turn of the drive gear. </li></ul>Figure 95–9 This gear combination provides an overdrive ratio of 0.33:1. Continued The driven gear is said to overdrive the drive gear. For this example, the gear ratio is 0.33:1. Ratios of 0.65:1 and 0.70:1 are typical automotive applications.
<ul><li>Idler Gears A gear that operates between the drive and driven gears is called a floating, or idler gear. They do not affect the speed relationship between the drive and driven gears; they do affect the direction of rotation. </li></ul>Figure 95–10 Idler gears affect the direction of rotation in a gear train, but not the final drive ratio. Continued Continued When an idler gear is installed between the drive and driven gears, both gears rotate in the same direction. Reverse gear on an automatic transmission often uses an idler gear to change the direction of rotation.
TORQUE, SPEED AND POWER <ul><li>Torque is a twisting force commonly expressed in pound-feet (lb-ft) or Newton-meters (N-m). Gears apply torque much like a wrench does; each tooth of a gear is actually a lever. </li></ul>Continued Figure 95–11 Gears apply torque in the same way a wrench applies torque—the force applied multiplied by the distance from the center of the gear equals the torque. On a gear with a 2-foot radius, applying a force of 10 pounds to one gear tooth exerts 20 lb-ft of torque on the center of the shaft to which the gear attaches.
<ul><li>Torque and Speed Relationship Torque and speed have an inverse relationship: as one goes up, the other goes down. With a constant input speed, transmission torque decreases as output speed increases. The opposite also applies assuming a constant input speed, transmission torque increases as output speed decreases. </li></ul>Continued
<ul><li>Torque Multiplication Levers can be used to increase or multiply torque. A wheel too heavy for a person to turn by muscle power alone turns easily when that same person uses a lever and fulcrum to multiply the applied force. </li></ul>Figure 95–12 A lever can be used to multiply torque, but it does so at the expense of distance or speed. Continued The force, or torque, increases at one end, but the lever must be moved a greater distance at the opposite end to obtain the increase in force. Either distance or speed must always be given up in order to increase, or multiply, torque.
<ul><li>Gears can be used in the same way as levers to multiply torque. When two gears of the same diameter are meshed, the driven gear will turn at the same speed as the drive gear. Since there is no difference in speed, there is no difference in torque between the two gears. If the drive gear is one-third the diameter of the driven gear, it must rotate three times for each rotation of the larger gear. This means that the larger gear will turn three times slower than the smaller gear. At the same time, the larger gear will exert three times the torque of the smaller gear. When speed decreases, torque increases. Torque multiplication and gear ratios are directly related. When a gear system is in reduction, there is more torque available at the driven gear, but less speed. </li></ul>Continued
<ul><li>Engine Torque Characteristics The torque curve of an engine shows how much torque is available at different points within a range of engine speeds. Because of these characteristics, torque multiplication must be provided between the crankshaft and drive axles to enable a vehicle to begin moving from a standstill and to accelerate at low speeds. Once engine RPM rises beyond the torque peak, a change in gear ratio brings engine speed back within the most efficient torque producing range. </li></ul>
POWER TRAIN GEAR RATIOS <ul><li>A transmission enables a vehicle to maximize engine torque, allowing the vehicle to move more efficiently. The transmission is aided in this task by the final drive gearing. These components work together to provide select gear ratios that take maximum advantage of engine torque available through various speed ranges. A gear ratio is determined by dividing the number of teeth on the driven gear (output) by the number of teeth on the driving gear (input). See Figure 95–13. </li></ul>Continued
Figure 95–13 Gear ratio is determined by dividing the number of teeth of the driven (output) gear (24 teeth) by the number of teeth on the driving (input) gear (12 teeth). The ratio illustrated is 2:1. <ul><li>The gear ratio represents the number of turns of the input gear to one turn of the output gear. A transmission/transaxle usually uses two pairs of gears to achieve each gear ratio, and there may be four, five, or six forward gears plus reverse. When two pairs of gears are used to create a gear, simply multiply the two ratios together to get the gear ratio. </li></ul>Continued
<ul><li>A low first-gear (high numerical) ratio creates a high amount of torque applied to the drive wheels to get the vehicle moving. </li></ul>Continued Continued <ul><li>Output shaft speed is a lot lower than engine speed. </li></ul><ul><li>Output torque is a lot higher than the engine is producing. </li></ul>First gear : Fifth gear : <ul><li>Output shaft speed is faster than the engine speed. </li></ul><ul><li>Output torque is lower than the engine is producing. </li></ul>
TRANSMISSION CONSTRUCTION <ul><li>A transmission is usually constructed of cast aluminum machined to accept the internal parts and strong enough to be a structural member of the drive train. The front of the transmission attaches to a separate bell housing or includes the bell housing as part of the casting of the transmission itself at the front of the transmission (toward the engine) in the front bearing retainer (sometimes called the quill ) that supports the clutch throwout (release) bearing and usually houses the front grease seal. </li></ul>Continued The rear of the transmission usually includes a separate casting called the extension housing . The center housing is usually referred to as the transmission case .
Figure 95–14 Cross section of a five-speed manual transmission showing the main parts. Continued
<ul><li>The input shaft is splined to the clutch disc and is also referred to as the main gear , clutch gear , or main drive pinion assembly . The main shaft , also called the output shaft , is splined at the end and transmits engine torque to the drive shaft (propeller shaft) through a yoke and universal shaft. All manual transmissions/transaxles use a countershaft (also called a lay shaft or cluster shaft ) to provide the other set of gears necessary to achieve the changes in gear ratios. The gears on the countershaft are called cluster gears or counter gears . See Figure 95–15. </li></ul>Continued
Figure 95–15 Cutaway of a six-speed manual transmission showing all of its internal parts. Continued
<ul><li>The size (77 mm or about 3 inches) is the distance between the center of the input shaft and the center of the countershaft. The greater this distance, the larger the transmission and the more torque it is capable of handling due to the larger gears. </li></ul>What Is Meant by a 77 mm Transmission?
<ul><li>The engine torque is applied to the input shaft when the clutch is engaged (clutch pedal up). This torque is applied to the main gear, which is in constant mesh with the countershaft gear. </li></ul>TORQUE FLOW THROUGH A MANUAL TRANSMISSION Continued HINT: The fact that the countershaft is revolving any time the clutch is engaged makes transmission noise diagnosis easier. The engine torque is multiplied by the ratio difference between the main gear and the cluster gear, then transferred and multiplied again when first gear is in mesh with the corresponding first gear on the main (output) shaft. The engine torque then is applied to the drive wheels.
SPEED GEARS <ul><li>All gears on the countershaft are permanently attached to the shaft. When the countershaft rotates, all gears on the countershaft rotate. The input shaft gear is also part of the input shaft. The gears on the main shaft are free to move on the shaft and are connected to the main shaft through the synchronizer hub when a shift is made. All speed gears use bearings that allow the speed gears to move independently of the main shaft. </li></ul>Continued
<ul><li>When assembling the main shaft and the countershaft, just remember that each shaft should look like a Christmas tree (tapered down from the top). When installed in the transmission, these two “Christmas trees” are meshed together with the small gear end of one shaft meshing with the large gear end of the other shaft. </li></ul>HINT: Figure 95–16 Notice that the countershaft and the main shaft both use gears of increasing size that mesh together.
SYNCHRONIZER PARTS AND OPERATION <ul><li>Most vehicles today in a manually shifted transmission use a floor-mounted shifter to change gears. The shifting lever either moves cables that transfer the shifting motion to the transmission or transaxle or move the shift forks directly. Inside the transmission/transaxle are shift forks that control shifts between two gears, such as first and second or second and third. Interlocks either in the shifter linkage itself or inside the transmission/transaxle prevent the accidental selection of reverse except when shifting from neutral and also prevent selecting two gears at the same time. See Figure 95–17. </li></ul>Continued
Figure 95–17 A typical shift mechanism showing the shift detents designed to not only give the driver a solid feel when shifting but also to prevent two gears from being selected at the same time. Continued
<ul><li>Synchronizers are used in manual transmissions/transaxles to make shifting easier. To synchronize means to make two or more events occur at the same time. When the driver depresses the clutch pedal, torque is no longer being transmitted to the input shaft and the drive wheels are “driving” the main shaft of the transmission/ transaxle. To achieve a clash-free (no grinding sound) shift, the shift speed must match the speed of the rotating gears. The detents and interlocks hold the shift mechanism in position. The real “shifting” in a synchromesh transmission takes place in the synchronizer assemblies , not the gears. Most synchronizer assemblies ride on the output shaft between two gears. </li></ul>Continued
<ul><li>A synchronizer assembly is named for the gears on either side of it, which are the two speeds that it engages. A five-speed transmission with constant-mesh reverse uses a 1–2 synchronizer, 3–4 synchronizer, and a 5-reverse synchronizer. </li></ul>Continued Synchronizer Construction Although there are number of design variations, all are similar and include a hub, a sliding sleeve , a stop ring , (or blocker rings or synchronizer ring ), keys , and springs . In addition, the tapered cone and coupling teeth machined on the speed gear are part of the synchronizer assembly. See Figure 95–18.
Figure 95–18 The shifter fork fits into the groove of the synchronizer sleeve. When a shift is made, the sleeve is moved toward the speed gear. The sleeve presses the stop ring (synchronizer ring) against the cone area of the speed gear. The friction between the stop ring and the speed gear causes the speed of the two to become equal, permitting the sleeve to engage the gear clutch teeth of the speed gear. When this engagement occurs, the shift is complete. Continued
<ul><li>In a typical synchronizer: </li></ul>Continued <ul><li>Splines attach the center hub of the synchronizer to the output shaft, so the hub and output shaft rotate together. There are also splines machined on the outer circumference of the hub. </li></ul><ul><li>An outer sleeve rides on the external hub splines with enough clearance so that it slides freely. The splines on the sleeve also match the small coupling teeth of the stop ring and speed gear. Coupling teeth are also called engagement or clutch teeth. The sleeve is splined to the hub, so it rotates with the output shaft. </li></ul>
<ul><li>In a typical synchronizer ( cont ): </li></ul>Continued <ul><li>A stop ring sits between the speed gear and the sleeve. The coupling teeth on the stop ring match those on both the sleeve and the speed gear. The stop ring also has a tapered cone to match the cone machined on the speed gear. </li></ul><ul><li>Small, spring-loaded detent keys, also called synchronizer keys or struts , ride in slots on the outer sleeve. The stop ring has slots to match these keys. This allows the stop ring to rotate slightly, relative to the sleeve, before the keys hit the sides of their slots and stop the stop ring. As the sleeve moves, the synchronizer keys move with it, which pushes the blocking ring onto the tapered cone of the speed gear. </li></ul>
<ul><li>Synchronizer Operation When the outer sleeve is centered on the hub, the synchronizer is in its neutral position—it does not contact either of the speed gears. To shift into gear, the driver disengages the clutch and moves the shift linkage. The shift linkage, which is described later in this chapter, pushes the sleeve toward one of the speed gears. As the sleeve moves, the detent keys push the stop ring toward the speed gear. This causes the ring cone to slide onto the tapered cone of the speed gear. See Figure 95–19. </li></ul>Continued
Figure 95–19 Typical synchronizer assembly. Continued
<ul><li>The speed gear is turning because it is in constant mesh with a countershaft gear. However, the gear may not be turning at the same speed as the synchronizer assembly even though both are on the same shaft. When the clutch is disengaged, the engine is no longer driving the transmission, so there is no torque applied to the input shaft, and the countershaft, or cluster gear, simply freewheels. As the shift is made, the stop ring acts as a brake to slow down the gear so that its speed matches the speed of the synchronizer assembly. That is, it synchronizes the shift. When the clutch disengages, the crankshaft drives the input shaft, which drives the countershaft, which drives the output shaft through the selected gear. </li></ul>Continued
<ul><li>The synchronizer goes through three stages during a shift: </li></ul>Continued <ul><li>The tapered surface, or cone, of the stop ring touches the speed gear first. As the two conical surfaces begin riding against each other, friction is created. See Figure 95–20. This causes the stop ring to move with the speed gear, but it moves only slightly until the detent keys hit the sides of their slots. This aligns the coupling teeth on the stop ring with the sleeve splines. Friction between the stop ring and cone slows the gear. </li></ul>
Figure 95–20 Synchronizer keys are attached to the clutch hub and push against the synchronizer ring when the sleeve is being moved during a shift. Notice the grooves on the synchronizer ring. These grooves prevent lubricating oil from becoming trapped between the ring and the cone surface of the speed gear. The grooves also help the ring release from the cone surface when a shift is made out of a gear. Continued
<ul><li>The sleeve overcomes the force of the detent key springs as the shift linkage continues to move it toward the gear. This allows the stop ring to relax and move slightly so that the sleeve splines begin to engage the coupling teeth on the stop ring. At this point, the coupling teeth on the stop ring and the speed gear may not line up with each other. However, friction continues to build between the ring and the cone, so the gear continues to slow down. </li></ul><ul><li>Once the sleeve, stop ring, and gear are all turning at the same speed, it takes just a small movement between the stop ring and gear to align the coupling teeth and allow the sleeve to slip completely over both sets. The speed gear is now locked to the output shaft through the synchronizer stop ring and sleeve. See Figure 95–21. </li></ul>Continued
Figure 95–21 A shift sequence starts when the shift fork is moved by the driver, (1) applying a force on the sleeve that moves it toward the speed gear. (2) The sleeve and the inserts contact the stop ring (blocking ring). (3) The synchronizer ring (stop ring) engages the cone on the speed gear, causing both assemblies to reach the same speed. (4) The shift is completed when the internal teeth of the sleeve mesh with the gear clutch teeth of the speed gear. Continued
<ul><li>Synchronizer stop rings are a simple type of clutch, called a cone clutch for the shape of the mating surfaces. Some manufacturers refer to the synchronizer action as “clutching.” Synchronizer sleeves and hubs are gear-quality steel. Stop rings are a softer metal—usually brass, copper, or a sintered metal—to absorb the friction of synchronizer operation. The tapered cone is relieved, that is grooves are machined into its contact surface. These grooves serve two purposes: </li></ul>Continued <ul><li>Channel excess lubricant out from between the two pieces for better contact. </li></ul><ul><li>Retain a small amount of lubricant. This decreases wear when the cone clutch must slip slightly during coupling tooth alignment. </li></ul>
<ul><li>The internal splines on the synchronizer sleeve and the coupling gear teeth on stop rings and speed gears have a special shape that works to hold the gear engaged once the driver releases the shift lever. The ends of the gear teeth are chamfered, giving them a triangular shape. These pointed ends allow easier sleeve-to-gear alignment as the angles tend to center the splines between the teeth. Once aligned, a back taper machined behind the chamfered end of the teeth and splines tends to keep the sleeve in place until the linkage pushes the sleeve away for another shift. Back taper is an angle cut opposite to the chamfer so that spline or tooth narrows just behind the chamfered end. See Figure 95–22. </li></ul>Continued
Figure 95–22 Before reassembling the transmission/transaxle, carefully inspect the splines on the synchronizer sleeves for wear. The shape of the splines helps prevent the transmission/transaxle from jumping out of gear during acceleration and deceleration. Continued
<ul><li>Some synchronizer stop rings have friction material on the cone surface. This paper friction material is the same as used on automatic transmission clutch plates, and provides a smoother synchronizing action than metal-to-metal contact. A manual transmission with paper stop rings must use automatic transmission fluid (ATF). Other lubricants damage the paper ring surface. See Figure 95–23. </li></ul>Continued
Figure 95–23 A three-piece synchronizer assembly. This type of synchronizer uses two cones, which helps achieve a smooth shift with less driver effort. Many newer transmissions/transaxles use a paper lining similar to that of the clutches in an automatic transmission. The transmissions/transaxles that have these paper linings must use automatic transmission fluid (ATF) for proper operation and long life. Continued
FIVE-SPEED GEARBOX TORQUE FLOW <ul><li>This section describes how power is transmitted through a typical five-speed gearbox. Although minor differences exist among different designs, the basic pattern of torque flow, also called power flow, is similar for most gearboxes. The concept of torque flow, or torque transfer, is the same for any transmission, regardless of the number of gear ratios available. The differences are in how the parts assemble and where they are located in the transmission. </li></ul>Continued
<ul><li>Five-Speed Transmission A five-speed transmission has six gear sets that provide five forward speeds and one reverse speed. Either a sliding gear or constant-mesh gears may be used for reverse. All forward gears are the constant-mesh type. The Borg-Warner T5 manual transmission serves as an example of a contemporary five-speed design. In addition to reverse, the T5 provides three gear reduction ratios (first, second, and third), direct drive (fourth), and an overdriven ratio (fifth). A sliding idler gear is used to change output shaft direction and provide reverse. </li></ul>Continued
<ul><li>Neutral In neutral , all of the synchronizer sleeves are centered on their hubs. Note that in this and the following illustrations the reverse idler shaft and sliding gear have been repositioned for clarity. In actuality, the assembly is positioned so it meshes with the reverse gears of the countershaft and output shaft simultaneously. With the clutch engaged, the drive gear of the input shaft turns the cluster gear, or countershaft. The speed gears are driven by the cluster gears, but rotate freely, on the output shaft. The output shaft may turn if the vehicle is moving or coasting, but no engine torque being transferred through the transmission. See Figure 95–24. </li></ul>Continued
Figure 95–24 In neutral, the input shaft and the countershaft are rotating if the clutch is engaged (clutch pedal up), but no torque is being transmitted through the transmission. Continued
<ul><li>First Gear In first gear , the shift linkage slides the 1–2 synchronizer sleeve rearward toward the first speed gear. The synchronizer assembly locks the speed gear to the output shaft. With the clutch engaged, the input shaft drives the countershaft, delivering engine torque to the gearbox. Torque transfers from the first counter gear to the first speed gear, which drives the output shaft through the 1–2 synchronizer hub splines. Torque flows through the transmission in gear reduction at the first gear ratio. See Figure 95–25. </li></ul>Continued
Figure 95–25 In first gear, the 1–2 synchronizer sleeve is moved rearward, locking the speed gear to the output shaft. Torque is transmitted from the input shaft to the countershaft and then to the output shaft. Continued
<ul><li>Second Gear In second gear , the shift linkage slides the 1–2 synchronizer sleeve forward, away from the first speed gear and toward the second speed gear. The synchronizer assembly releases first gear, then locks the second speed gear to the output shaft. With the clutch engaged, the input shaft is driven at crankshaft speed and turns the countershaft. Engine torque transfers from the second counter gear to the second speed gear, which drives the output shaft through the 1–2 synchronizer hub splines. Torque flows through the transmission in gear reduction at the second gear ratio. See Figure 95–26. </li></ul>Continued
Figure 95–26 In second gear, the 1–2 synchronizer sleeve is moved forward, which locks the second speed gear to the output shaft. Continued
<ul><li>Third Gear In third gear , the shift linkage centers the 1–2 synchronizer sleeve and moves the 3–4 synchronizer sleeve back toward the third speed gear. The synchronizer assembly locks the third speed gear to the output shaft. With the clutch engaged and the input shaft driving the countershaft, the third counter gear transfers torque to the third speed gear. The speed gear drives the output shaft through the 3–4 synchronizer hub splines. Torque flows through the transmission in gear reduction at the third gear ratio. See Figure 95–27. </li></ul>Continued
Figure 95–27 To achieve third gear, the shaft linkage first centers the 1–2 synchronizer sleeve and then moves the 3–4 synchronizer sleeve rearward, locking third gear to the output shaft. Continued
<ul><li>Fourth Gear In fourth gear , the shift linkage moves the 3–4 synchronizer sleeve forward, away from the third speed gear and toward the input shaft drive gear. The synchronizer assembly locks the input shaft drive gear to the output shaft. With the clutch engaged, the input shaft drives the output shaft through the 3–4 synchronizer hub splines and both shafts rotate at crankshaft speed. Torque flows straight through the transmission at a 1:1 ratio, delivering engine torque to the drive shaft. This is called direct drive because there is no gear reduction through the transmission. The counter gears also turn because they are in constant mesh, but they do not affect torque flow because all of the speed gears are freewheeling on the output shaft. See Figure 95–28. </li></ul>Continued
Figure 95–28 In fourth gear, the 3–4 synchronizer sleeve is moved forward, which locks the fourth speed gear to the output shaft. Continued
<ul><li>Fifth Gear In fifth gear , shift linkage centers the 3–4 synchronizer sleeve and moves the fifth synchronizer sleeve toward the fifth speed gear. On the T5 transmission the synchronizer assembly locks the fifth speed gear to the countershaft. The speed gear drives a fixed gear on the output shaft.to the countershaft, so it is driven and driving the speed gear when fifth gear is engaged. This transfers torque to the output shaft through the fixed fifth gear. Note the countershaft gear is larger than the output shaft gear. Therefore, fifth gear is overdriven. Torque flows through the transmission at the fifth gear, or overdrive, ratio. Typical overdrive gear ratios are between 0.6:1 and 0.8:1. This lowers engine speed for economical highway cruising. See Figure 95–29. </li></ul>Continued
Figure 95–29 To achieve fifth gear, the shift linkage first centers the 3–4 synchronizer sleeve and then moves the fifth synchronizer sleeve toward the fifth speed gear, locking it to the output shaft. Continued
<ul><li>On some five-speed transmissions, the fifth speed gear is on the output shaft with the other speed gears. This type of arrangement is typically used with constant-mesh reverse gears. In these designs, fifth and reverse gears share a synchronizer assembly. The fixed countershaft gear drives the speed gear, which drives the output shaft through the hub splines when the sliding sleeve is engaged. Torque flow through the transmission is similar to any of the gear reduction forward speeds detailed above, but the speed gear is generally overdriven. </li></ul>Continued
<ul><li>Reverse Two common reverse gear designs: </li></ul>Continued <ul><li>Sliding gear </li></ul><ul><li>Constant-mesh gear. </li></ul>With a sliding reverse gear design, such as on the T5, the shift linkage slides the reverse idler gear on its shaft until it engages the reverse gears on the countershaft and output shaft gear. Both gears are fixed to their respective shafts. This design uses spur gears for reverse, not helical gears, because the gear teeth must move into and out of mesh. On some gearboxes, the sliding gear splines to the output shaft. The linkage moves the gear along the output shaft splines to engage the reverse idler gear.
<ul><li>An unusual feature of the Borg-Warner T5 is that it does not have a separate reverse output shaft gear. Spur teeth machined around the outside of the 1–2 synchronizer sleeve act as the reverse output gear. When the T5 is shifted into reverse, the linkage moves the reverse idler gear rearward so it simultaneously meshes with the countershaft reverse gear and the gear on the synchronizer sleeve. </li></ul><ul><li>See Figure 95–30. </li></ul>Continued
Figure 95–30 Torque flows through the transmission in reverse gear. Note that the idler gear drives the 1–2 synchronizer sleeve gear, which is splined to the output shaft. Continued
<ul><li>When the clutch is engaged, the countershaft is driven and the reverse gear drives the idler gear, which rotates in the opposite direction of the countershaft. The idler gear drives the 1–2 synchronizer sleeve, so there is another directional change in rotation. Although the sleeve is not engaged to a speed gear, it remains splined to the output shaft, so the sleeve drives the output shaft when the idler gear is engaged. The output shaft rotates in the opposite direction of the input shaft because the idler gear is between them. With constant - mesh gears , the shift linkage moves the 5-reverse synchronizer sleeve away from the fifth speed gear and toward the reverse speed gear when reverse is selected. </li></ul>Continued
<ul><li>Typically, no stop ring is used between the synchronizer sleeve and the reverse gear, so the output shaft must be stopped to engage reverse without grinding the sleeve splines against the coupling teeth of the reverse gear. The synchronizer assembly locks the reverse speed gear to the output shaft. With the clutch engaged, the input shaft drives the countershaft. The reverse counter gear drives the reverse idler gear, which drives the reverse speed gear in the direction opposite normal rotation. The reverse speed gear drives the output shaft through the 5-reverse synchronizer hub splines. Torque flows through the transmission in gear reduction at the reverse gear ratio. The output shaft turns opposite its normal direction of rotation, so the vehicle moves to the rear. </li></ul>Continued
Figure 95–31 Cutaway of a T5 five-speed transmission showing all of its internal parts. Continued
MANUAL TRANSAXLE CONSTRUCTION <ul><li>A manually shifted transaxle includes an input shaft, an output shaft, and a differential assembly all in one case. The input shaft is attached to the clutch, which transfers engine torque from the engine flywheel to the input shaft when the clutch is engaged. Most transaxles use speed gears and synchronizers on both the input and output shafts, as shown in Figure 95–32. The differential assembly, also called a final drive assembly , attaches to the output shaft and splits the torque to both front drive axles. See Figure 95–33. </li></ul>Continued
Figure 95–32 Notice that this five-speed transaxle from a Dodge/Plymouth Neon uses synchronizers on both the input and output shafts. Continued
Figure 95–33 Cutaway of a typical manual transaxle showing all of its internal parts including the final drive assembly. Continued
TRANSMISSION/TRANSAXLE REMOVAL <ul><li>Before removing the transmission/transaxle for service, double-check that the problem is not due to any malfunction of the clutch or shift linkage. To remove a transmission or transaxle, always follow the procedure in the service manual to be assured of doing no harm to either the vehicle or to yourself. </li></ul>Continued
<ul><li>Steps typically involved in the removal and disassembly include : </li></ul>Figure 95–34 When the transmission/transaxle is removed from the vehicle, the engine must be supported. In this case, the engine oil pan is supported with a block of wood to spread the load across the entire oil pan to prevent damage. The block of wood is placed on top of a tall safety stand that allows room for the service technician to work while standing. Continued <ul><li>Disconnecting the negative battery cable </li></ul><ul><li>Safely hoisting and supporting the vehicle </li></ul><ul><li>Supporting the engine with a holding fixture or other support (front-wheel-drive) </li></ul><ul><li>Removing the drive axle shafts or drive shaft (rear-wheel- drive) </li></ul>
<ul><li>Steps typically involved in the removal and disassembly include : </li></ul>Continued <ul><li>Removing the clutch linkage and shift linkage (see Figures 95–35 and 95–36) </li></ul><ul><li>Disconnecting the vehicle speed sensor and reverse (backup) light connectors </li></ul><ul><li>Removing the attaching bolts/nuts from the engine and transmission/ transaxle mounts and then removing the unit from the vehicle </li></ul>
Figure 95–36 Typical cable-operated shift linkage used on a front-wheel-drive transaxle. Figure 95–35 A transmission from a restored muscle car from the 1970s. Notice the use of external control rod shift linkage. Continued
Figure 95–37a Saturn drivetrain is removed as an assembly along with the cradle. <ul><li>Sometimes it is easier to remove the entire power train (engine and transaxle as an assembly) from the vehicle, as shown at right. When the entire assembly has been removed from the vehicle, often the transaxle can then be removed from the engine. </li></ul>Continued
Figure 95–37b The transaxle can now be easily removed from the cradle and the engine. Continued
TRANSMISSION/TRANSAXLE DISASSEMBLY <ul><li>Before disassembling the transmission/transaxle, drain any remaining gear lubricant from the unit and dispose of it properly. </li></ul>Continued CAUTION: Most extreme pressure (EP) lubricants contain sulfur compounds cause skin irritation. Wear protective gloves or wash hands thoroughly using soap and water after exposure to used gear lubricant. Mount the transmission/transaxle on a holding fixture or place it on a large, clean work surface. The removal of the shifter housing allows the tech to see any obvious damage as well as providing the opportunity to check the shift forks, which are frequently worn in manually-shifted transmissions/transaxles. See Figures 95–38 and 95–39.
Figure 95–38 The shift forks should be inspected for wear. Figure 95–39 The cost to replace these gears may exceed the cost of a replacement transmission. Continued
<ul><li>The disassembly and reassembly of a manual transaxle is similar to that for a manual transmission except for the addition of the final drive unit. Some transaxles require two people for disassembly and reassembly because often the shift linkage has to be held in place while assembled components are placed into the case. See Figure 95–40. </li></ul>Continued CAUTION: Most extreme pressure (EP) lubricants contain sulfur compounds that can cause skin irritation. Either wear protective gloves or wash your hands thoroughly using soap and water after exposure to used gear lubricant.
Figure 95–40 It often requires two people to assemble a transaxle because the shaft with the shifter forks needs to be placed into the case as an assembly, as on this unit. Continued
<ul><li>Check the service manual for the exact disassembly procedures to follow for the unit being serviced. Sometimes the main shaft is removed through the rear of the transmission and sometimes it is removed through the top of the case. Also look for hidden snap rings. See Figures 95–41 and 95–42. </li></ul>Continued HINT: The fact that the countershaft is revolving any time the clutch is engaged makes transmission noise diagnosis easier.
Figure 95–41 (a) During the disassembly of any manual transmission/transaxle, carefully check for the location of the snap rings. Often they are hidden. Consult the factory service manual or unit repair manual for information and procedures for the unit being serviced Continued
Figure 95–41 (b) Using snap-ring pliers to remove a snap ring. Many snap rings have an “up” side. Be sure to reinstall any snap rings in the correct direction. Continued
Figure 95–41 (c) After the snap ring is removed, some components can be simply lifted off the main shaft, while other gears may require the use of a press. Continued
Figure 95–42 (a) Many gears require that a hydraulic press be used to separate the gear(s) from the shaft. After double-checking that all snap ring retainers have been removed and after checking in the service manual to see which gear needs to be pressed off, carefully position the “bearing splitter” as far inward as possible to avoid damaging the teeth during the pressing operation. Continued
Figure 95–42 (b) For safety, place an old brake drum over the gear(s) being pressed off. If the gear were to shatter, the parts will be trapped inside the brake drum. Continued
Figure 95–42 (c) Some transmission disassembly and reassembly procedures require the use of special pullers, such as this tool being used on a NV 4500 transmission.
<ul><li>A wise technician once told a beginning technician to remember these items when working with transmissions: </li></ul>Manual Transmission Service Tips <ul><li>Always use a brass or plastic hammer when pounding on a steel or aluminum component. </li></ul><ul><li>If using a steel hammer, always use a brass or aluminum punch or place wood between the steel components and the hammer. </li></ul><ul><li>Many parts can be installed in either direction but usually only one way is correct. </li></ul><ul><li>If you are exerting a lot of force, you are probably doing something wrong. </li></ul><ul><li>Many drivetrain parts are pulled or pressed off and pressed or driven on. </li></ul>
HARD-TO-SHIFT PROBLEM DIAGNOSIS <ul><li>Several items that could be worn or defective can cause a manual transmission/transaxle to be difficult to shift: </li></ul>Continued <ul><li>Clutch not fully disengaging If the clutch linkage is not properly adjusted or if there is a leak in the hydraulic clutch linkage, the clutch may not be fully disengaged. A shift is very difficult, if not impossible, if engine torque is being transferred through the transmission/transaxle as a shift is being attempted. </li></ul><ul><li>Worn synchronizer If the synchronizer rings are worn, the rings will be unable to properly match the speed gear speed, making the shift difficult and/or creating gear clash (noise) when shifting. </li></ul>
<ul><li>Worn, cracked, or loose shift forks If there is a problem with shift forks, the synchronizer cannot be properly moved during a shift attempt, making shifting difficult, if not impossible. If one fork is worn or defective, engaging two gears is likely. </li></ul><ul><li>Excessive input- or main-shaft end play Excessive end play in the input or main shaft will cause the gears to move away from the synchronizer assembly, resulting in grinding during shifts or shifts that are difficult or impossible to complete. </li></ul><ul><li>Improper lubrication Many of today’s manual transmissions use synchronizer rings (blocking rings) that are lined with compounds, paper, or other friction material. All of these transmissions/transaxles must be filled with the proper fluid formulated for proper shifting. </li></ul>Continued
<ul><li>A vehicle equipped with a manual transmission had to be repaired several times for worn shift forks. Even though the vehicle warranty paid for the repair, both the customer and the service department personnel were concerned about the repeated failures. All technical service bulletins (TSBs) were checked to see if there was an updated, improved shift fork. No luck. Even the manufacturer’s technical assistance personnel were unable to determine why the shift forks were wearing out. After the third repair, the service technician rode with the customer to see if the cause could be determined. As the woman driver got into the driver’s seat, she placed the handle of her purse over the shifter on the floor and allowed the purse to hang from the shifter. </li></ul>The Worn Shift Fork Mystery - Part 1
<ul><li>The technician asked the owner if she always placed her purse on the shifter and when she said yes, the technician knew immediately the cause of the worn shift forks. The purse exerted a force on the shifter all the time. This force pushed the shift forks against the synchronizer sleeve. Because the sleeve rotates all the time the vehicle is in motion, the shift forks were quickly worn. The service technician should have determined the root cause of the problem after the first repair. The customer agreed to find another location for her purse so that the transmission problem would not reoccur. </li></ul>The Worn Shift Fork Mystery - Part 2 NOTE: A worn synchronizer sleeve and/or blocking ring can cause the transmission/transaxle to pop out of gear while accelerating or decelerating.
MANUAL TRANSMISSION INSTALLATION <ul><li>When installing a repaired or replacement transmission/transaxle, the clutch should be carefully inspected and replaced as necessary. The clutch friction disk must be held in position using an alignment tool (sometimes called a dummy shaft ) that is secured in the pilot bearing. This holds the disk in position while the pressure plate is being installed. Finally, the engine bell housing is put on the engine, if it was not installed before. The alignment of this type of bell housing is then checked. </li></ul>Continued
<ul><li>The clutch release yoke should be checked for free movement. Usually, the clutch release bearing is replaced, ensuring that the new bearing is securely attached to the clutch release yoke. The transmission can then be installed. The clutch shaft must be guided straight into the clutch disk and pilot bearing. The clutch shaft is rotated, as required, to engage in the splines of the clutch disk. The assembly bolts are secured when the transmission fully mates with the bell housing. </li></ul>CAUTION: Perfectly round cylinders can be distorted whenever another part of the engine is bolted and torqued to the engine block. For example, it has been determined that after the cylinders are machined, the rear cylinder bore can be distorted as much as 0.006 inch (0.15 millimeter) out-of-round after the bell housing is bolted onto the block! To help prevent this distortion, always apply the specified torque to all fasteners going into the engine block and tighten in the recommended sequence.
<ul><li>Complete the installation by attaching the transmission/ transaxle mount, driveshaft (drive axle shafts), vehicle speed sensor, and reverse (backup) light switch. </li></ul>Continued CAUTION: Always adjust the clutch free play before starting the engine to help prevent thrust bearing damage.
GEAR LUBRICATION <ul><li>After installation of the transmission/transaxle, the unit should be filled with the correct lubricant. The various lubricants, their general use, and their American Petroleum Institute (API) rating: </li></ul>Continued GL-1 Straight mineral oil GL-2 Worm-type gear lubricant GL-3 Mild-type EP lubricant (will not protect hypoid gears) GL-4 ‑EP-type lubricant (OK for manual transmissions/transaxles) GL-5 EP-type ok for hypoid gears and for Mil-L2150B (military) CAUTION: Failure to use the specified manual transmission/transaxle lubricant could cause hard shifting and possible transmission damage.
<ul><li>Manual transmissions/transaxles require one of the following: </li></ul>Figure 95–43 Some manual transmissions/transaxles require synchromesh transmission fluid. <ul><li>SAE 80W-90 (GL-4) gear lube </li></ul><ul><li>STF (synchromesh transmission fluid), but with friction characteristics designed for manual transmissions (see Figure 95–43) </li></ul><ul><li>ATF (automatic transmission fluid) </li></ul><ul><li>Engine oil (usually SAE 5W-30) </li></ul>Continued
<ul><li>Sometimes parts do not seem to line up correctly. Try this tip the next time. Cut the head off extra-long bolts that are of the same diameter and thread as those being used to retain the part, such as a transmission. </li></ul>Figure 95–44 Headless, long bolts can be used to help install a transmission to the engine. The Headless Bolt Trick Use a hacksaw to cut a slot in the end of these guide bolts for a screwdriver slot.Install the guide bolts; then install the transmission. Use a straight-blade screwdriver to remove the guide bolts after securing the transmission with the retaining bolts.
SUMMARY <ul><li>A transmission is required both to provide the torque necessary to the drive wheels to get the vehicle moving from a stop and to provide economical cruising on the highway. </li></ul><ul><li>A gear ratio is determined by dividing the number of teeth on the driven gear (output) by the number of teeth on the driving gear (input). A ratio is always expressed as a number relative to one rotation of the output gear. </li></ul><ul><li>An overdrive ratio is a ratio that results in the output gear rotating faster than the input gear; the first number of this ratio is less than one. </li></ul><ul><li>A spur gear is a gear with straight teeth, and a helical-cut gear is a gear with angled teeth. </li></ul>Continued
SUMMARY <ul><li>The input shaft is splined to the clutch disc. The output shaft is also called the main shaft. </li></ul><ul><li>A countershaft is another shaft inside a transmission/transaxle which provides another set of gears to produce the necessary gear ratios. </li></ul><ul><li>Care should be taken to not damage the parts of the transmission/ transaxle during disassembly. Always consult the factory service manual for the exact procedures to follow, especially regarding using a hydraulic press to press gears off or on the shafts. </li></ul><ul><li>A synchronizer assembly permits a shift to be made without gear clash. </li></ul>Continued ( cont. )
SUMMARY <ul><li>The parts of a typical synchronizer include the synchronizer sleeve, hub, and ring. </li></ul><ul><li>A transaxle includes a final drive unit that splits the torque to the two front drive wheels and allows the drive wheels to rotate at different speeds while traveling around a corner or over bumpy roads. </li></ul><ul><li>A manual transmission/transaxle may use one of four possible lubricants including gear lube, synchromesh transmission fluid (STF), automatic transmission fluid (ATF), or engine oil. </li></ul>( cont. )