Chap97

Prepare for ASE Suspension and Steering (A4) certification test content area “C” (Related Suspension and Steering Service). Explain how to perform a U-joint inspection. List the steps necessary to replace a U-joint. Explain how to perform a measurement of the working angles of a U-joint. OBJECTIVES: After studying Chapter 97, the reader should be able to: Continued

Describe the service procedures for replacing CV joints and boots. Describe the routine maintenance service procedures required for drive axle shafts and universal CV joints. OBJECTIVES: After studying Chapter 97, the reader should be able to:

Inclinometer pin bushings • pinch bolt spline bind • synthetic retainers torque prevailing nut U-joints KEY TERMS:

The driveshaft of a typical rear-wheel-drive (RWD) vehicle rotates about three times faster than the wheels. This is due to the gear reduction that occurs in the differential. The driveshaft rotates at the same speed as the engine if the transmission ratio is 1 to 1 (1:1). The engine speed, in revolutions per minute (RPM), is transmitted through the transmission at the same speed.

The owner of a pickup truck complained that a squeaking noise occurred while driving in reverse. The “ eeeee - eeeee - eeee ” sound increased in frequency as the truck increased in speed, yet the noise did not occur when driving forward. Because there was no apparent looseness in the U-joints, the service technician at first thought that the problem was inside either the transmission or the rear end. When the driveshaft was removed to further investigate the problem, it became obvious where the noise was coming from. The U-joint needle bearing had worn the cross-shaft bearing surface of the U-joint. The noise occurred only in reverse because the wear had occurred in the forward direction, and therefore only when the torque was applied in the opposite direction did the needle bearing become bound up and start to make noise. A replacement U-joint solved the squeaking noise in reverse. The Squeaking Pickup Truck - Part 1

Figure 97–1 Notice how the needle bearings have worn grooves into the bearing surface of the U-joint. The Squeaking Pickup Truck - Part 2

DRIVESHAFT AND U-JOINT INSPECTION The driveshaft should be inspected for the following: Continued CAUTION: A dented or creased driveshaft can collapse, especially when the vehicle is under load. This collapse of the driveshaft can cause severe damage to the vehicle and may cause an accident. Any dents or creases caused by incorrect hoisting of the vehicle or by road debris. Undercoating, grease, or dirt buildup on the driveshaft can cause a vibration. Undercoating should be removed using a suitable solvent and a rag. Always dispose of used rags properly.

Figure 97–2 All U-joints and spline collars equipped with a grease fitting should be greased four times a year as part of a regular lubrication service. The U - joints should be inspected every time the vehicle chassis is lubricated, or four times a year. Original equipment (OE) U-joints are permanently lubricated and have no provision for greasing. If there is a grease fitting, the U-joint should be lubricated by applying grease with a grease gun. See Figure 97–3. Continued

Figure 97–3 Many U-joints require a special grease gun tool to reach the grease fittings. Continued Continued

U-joints can be defective and not show noticeable free movement. Continued A proper U-joint inspection can be performed only by removing the driveshaft from the vehicle. NOTE: U-joints are not serviceable items and cannot be repaired. If worn or defective, they must be replaced. In addition to periodic lubrication, the driveshaft should be grabbed and moved to see if there is any movement of the U-joints. If any movement is noticed when the driveshaft is moved, the U-joint is worn and must be replaced.

Before removing the driveshaft, always mark the position of all mating parts to ensure proper reassembly. White correction fluid, also known as “White Out” or “Liquid Paper,” is an easy and fast-drying marking material. Figure 97–4 Always mark the original location of U-joints before disassembly. Continued

Figure 97–5 Two types of retaining methods that are commonly used at the rear U-joint at the differential. To remove the driveshaft from a rear-wheel-drive vehicle, remove the four fasteners at the rear U-joint at the differential. Push the driveshaft forward toward the transmission and then down and toward the rear of the vehicle. The driveshaft should slip out of the transmission spline and can be removed from underneath the vehicle. Continued

Figure 97–6 The best way to check any U-joint is to remove the driveshaft from the vehicle and move each joint in all directions. A good U-joint should be free to move without binding. To inspect U-joints, move each joint through its full travel, making sure it can move (articulate) freely and equally in all directions. NOTE: With the driveshaft removed, transmission lubricant can leak out of the rear extension housing. To prevent a mess, use an old spline the same size as the one being removed or place a plastic bag over the extension housing to hold any escaping lubricant. A rubber band can be used to hold the bag onto the extension housing.

U-JOINT REPLACEMENT All movement in a U-joint should occur between the trunnions and the needle bearings in the end caps. The end caps are press-fit to the yokes, which are welded to the driveshaft. Three types of retainers are used to keep bearing caps on U-joints: After removing the retainer, use a press or a vise to separate the U-joint from the yoke. See Figure 97–9. Continued The outside snap ring. See Figure 97–7 The inside retaining ring. See Figure 97–8 Injected synthetic (usually nylon)

Figure 97–7 Typical U-joint that uses an outside snap ring. This style of joint bolts directly to the companion flange that is attached to the pinion gear in the differential. Figure 97–8 Removing an inside retaining ring (snap ring). Continued

Figure 97–9 Use a vise and two sockets to replace a U-joint. One socket fits over the bearing cup and one fits on the bearing to press fit the cups from the crosspiece. Continued

When removing a driveshaft, use tape to prevent the rear U-joint caps from falling off. If the caps fall off the U-joint, all of the needle bearings will fall out and scatter over the floor. Use Tape to be Safe Figure 97–10 Taping the U-joint to prevent the caps from coming off.

Figure 97–11 A special tool being used to press apart a U-joint that is retained by injected plastic. Heat from a propane torch may be necessary to soften the plastic to avoid exerting too much force on the U-joint. U-joints that use synthetic retainers must be separated using a press and a special tool to press onto both sides of the joint in order to shear the plastic retainer, as shown here. Continued

Replacement U-joints use spring clips instead of injected plastic. Remove the old joint from the yoke, and replace with a new one. Continued NOTE: If a U-joint is slightly stiff after being installed, strike the U-joint using a brass punch and a light hammer. This often frees a stiff joint and is often called “relieving the joint.” The shock aligns the needle bearings in the end caps. Replacement U-joints should be forged (never cast) and use up to 32 needle bearings (also called pin bushings ) instead of just 24 needle bearings, as used in lower-quality U-joints. Replacement U-joints usually have a grease fitting so that the new replacement U-joint can be properly lubricated. See Figures 97–12 and 97–13.

Figure 97–13 When installing a new U-joint, position the grease fitting on the inboard side (toward the driveshaft tube) and in alignment with the grease fitting of the U-joint at the other end. After removing any dirt or burrs from the yoke, press in a new U-joint. Rotate the new joint after installation to make sure it moves freely, without binding or stiffness. If a U-joint is stiff, it can cause a vibration. Figure 97–12 Removing the worn cross from the yoke. Continued

U-JOINT WORKING ANGLES Unequal or incorrect U-joint working angles can cause severe vibrations. driveshaft and U-joint angles may change from the original factory setting due to one or more of the following: Continued Defective or collapsed engine or transmission mounts Defective or sagging springs, especially the rear springs due to overloading or other causes Accident damage or other changes to the chassis of the vehicle Vehicle modification that raises or lowers the ride height

Replace any engine or transmission mount that is cracked or collapsed. When a mount collapses, the engine drops from its original location. Now the driveshaft angles are changed and a vibration may be felt. Rear springs often sag after many years of service or after being overloaded. This is especially true of pickup trucks. Many people carry as much as the cargo bed can hold, often exceeding the factory-recommended carry capacity or gross vehicle weight (GVW) of the vehicle. To measure U-joint and driveshaft angles, the vehicle must be hoisted using an axle contact or drive-on-type lift so as to maintain the same driveshaft angles as the vehicle has while being driven. Continued

Figure 97–14 The working angle of most U-joints should be at least 1/2 degree (to permit the needle bearing to rotate in the U-joints) and should not exceed 3 degrees or a vibration can occur in the driveshaft, especially at higher speeds. The difference between the front and rear working angles should be within 1/2 degree of each other. The working angles of the two U-joints on a driveshaft should be within 1/2 degree of each other in order to cancel out speed changes. Continued

To measure the working angle: Figure 97–15 Inclinometer reads 19 1/2 degrees at this rear U-joint. Step # 1 Place an inclinometer (a tool used to measure angles) on the rear U-joint bearing cap. Level the bubble and read the angle. At right, the pictured reading is 19.5 degrees. Step #2 Rotate the driveshaft 90 degrees and read the angle of the rear yoke. This reading is 17 degrees. Step #3 Subtract the smaller reading from the larger reading to obtain the working angle of the joint. Here, it is 2.5 degrees (19.5 - 17 = 2.5 degrees). Continued

Figure 97–16 Placing a tapered metal wedge between the rear leaf spring and the rear axle pedestal to correct rear U-joint working angles. Repeat the same procedure for the front U-joint. The front and rear working angles should be within 0.5 degrees. If the two working angles are not within 0.5 degrees, shims can be added to bring the two angles closer together. The angle of the rear joint is changed by installing a tapered shim between the leaf spring and the axle, as shown here. Continued

Angle of the front joint is changed by adding or removing shims from the mount under the transmission. Figure 97–17 A transmission oil pan gasket leak allowed automatic transmission fluid (ATF) to saturate the rear transmission mount rubber, causing it to collapse. After replacing the defective mount, proper driveshaft angles were restored and the driveline vibration was corrected. CAUTION: Use caution when using wedges between the differential and the rear leaf spring to restore the correct U-joint working angle. Even though wedges are made to raise the front of the differential, the tilt often prevents rear-end lubricant from reaching the pinion bearing, resulting in pinion bearing noise and eventual failure.

CV JOINT DIAGNOSIS When a CV joint wears or fails, the most common symptom is noise while driving. An outer fixed CV joint will most likely be heard when turning sharply and accelerating at the same time. This noise is usually a clicking sound. While inner joint failure is less common, a defective inner CV joint often creates a loud clunk while accelerating from rest. To help verify a defective joint, drive the vehicle in reverse while turning and accelerating. This almost always will reveal a defective outer joint.

Whenever a driveline clunk is being diagnosed, one possible cause is excessive backlash (clearance) between the ring gear teeth and differential pinion teeth in the differential. Another cause of excessive differential backlash is too much clearance between differential carrier pinion teeth and side gear teeth. A quick test to check backlash involves three steps: Quick and Easy Backlash Test Step #1 Hoist the vehicle on a frame contact lift, allowing the drive wheels to be rotated. Step #2 Have an assistant hold one drive wheel and the driveshaft to keep them from turning. Step #3 Move the other drive wheel, observing how far the tire can rotate. This is the amount of backlash in the differential; it should be less than 1 in. (25 mm) of movement measured at the tire. If the tire can move more than 1 in. (25 mm), then the differential should be inspected for wear and parts should be replaced as necessary. If the tire moves less than 1 in. (25 mm), then the backlash between the ring gear and pinion is probably not the cause of the noise.

REPLACEMENT SHAFT ASSEMBLIES Front-wheel-drive vehicles were widely used in Europe and Japan long before they became popular in North America. The standard repair procedure used in these countries is the replacement of the entire drive assembly if there is a CV joint failure. Replacement boot kits are rarely seen in Europe because it is felt that even a slight amount of dirt or water inside a CV joint is unacceptable. Vehicle owners simply wait until the joint wear causes severe noise, and the entire assembly is replaced. The entire drive axle shaft assembly can easily be replaced and the defective unit can be sent for remanufacturing. Continued

CV JOINT SERVICE The hub nut must be removed whenever servicing a CV joint or shaft assembly on a front-wheel-drive vehicle. Since these nuts are usually torqued to almost 200 lb-ft (260 N-m), keep the vehicle on the ground until the hub nut is loosened. Continued Continued Figure 97–18 The hub nut must be removed before the hub bearing assembly or drive axle shaft can be removed from the vehicle.

Follow these steps: Figure 97–19 Many knuckles are attached to the ball joint on the lower control arm by a pinch bolt. NOTE: Most manufacturers warn against using an air impact wrench to remove the hub nut. The impacting force can damage the hub bearing. Step #1 Remove the front wheel and hub nut. Continued Lower ball joint or pinch bolt. Tie rod end. See Figure 97–20 Stabilizer bar link. Front disc brake caliper. Step #2 To allow the knuckle room to move outward enough to remove the drive axle shaft, disconnect the following: Continued

Figure 97–20 The preferred method for separating the tie rod end from the steering knucke is to use a puller such as the one shown. A “pickle-fork”-type tool should be used only if the tie rod is going to be replaced. A pickle-fork-type tool can damage or tear the rubber grease boot. Continued

Step #3 Remove the splined end of the axle from the hub bearing. Sometimes a special puller may be necessary, but in most cases the shaft can be tapped inward through the hub bearing with a light hammer and a brass punch can be used. Figure 97–21 Many drive axles are retained by torque prevailing nuts that must not be reused. Torque prevailing nuts are slightly deformed or contain a plastic insert that holds the nut tight (retains the torque) to the shaft without loosening. Continued See Figure 97–22. To protect the threads of the drive axle shaft, install the hub nut temporarily.

Figure 97–22 A special GM tool is being used to separate the drive axle shaft from the wheel hub bearing. Continued

Figure 97–23 Most inner CV joints can be separated from the transaxle with a prybar. Step #4 Use a prybar or special tool with a slide hammer, as shown below, and remove the inner joint from the transaxle. Step #5 Disassemble, clean, and inspect all components. See Figures 97–24 through 97–30. Continued

Figure 97–24 When removing a drive axle shaft assembly, use care to avoid pulling the plunge joint apart. Continued

Figure 97–25 If other service work requires that just one end of the drive axle shaft be disconnected from the vehicle, be sure that the free end is supported to prevent damage to the protective boots or allowing the joint to separate. The method shown using a shop cloth to tie up one end may not be very pretty, but at least the technician took precautions to support the end of the shaft while removing the transaxle to replace a clutch. Continued

Figure 97–26 With a scribe, mark the location of the boots before removal. The replacement boots must be in the same location. Figure 97–27 Most CV joints use a snap ring to retain the joint on the drive axle shaft. Continued

Figure 97–28 After releasing the snap ring, most CV joints can be tapped off the shaft using a brass or shot-filled plastic (dead-blow) hammer. Continued Figure 97–29 Typical outer CV joint after removing the boot and the joint from the drive axle shaft. This joint was removed from the vehicle because a torn boot was found. After disassembly and cleaning, this joint was found to be OK and was put back into service. Even though the grease looks terrible, there was enough grease in the joint to provide enough lubrication to prevent any wear from occurring.

Figure 97–30 The cage of this Rzeppa-type CV joint is rotated so that one ball at a time can be removed. Some joints require that the tech use a brass punch and a hammer to move the cage. Continued

Figure 97–31 Be sure to use all of the grease supplied with the replacement joint or boot kit. Use only the grease supplied and do not use substitute grease. Step #6 Replace the entire joint if there are any worn parts. Pack all the grease that is supplied into the assembly or joint. Assemble the joint and position the boot in the same location as marked. Before clamping the last seal on the boot, be sure to release trapped air to prevent the boot from expanding when heated and collapsing when cold. This is sometimes called burping the boot. Clamp the boot to manufacturer’s specs. Continued

Figure 97–32 A screwdriver is shown, but a punch would be better, to keep the rotor from rotating while removing or installing the drive axle shaft spindle nut. Step #7 Reinstall the drive axle shaft in the reverse order of removal, and torque the drive axle nut to factory specs.

The owner of a front-wheel-drive Buick complained that it vibrated during acceleration only. The vehicle would also pull toward one side during acceleration. An inspection discovered a worn (cracked) engine mount. After replacing the mount, the CV joint angles were restored and both the vibration and the pulling to one side during acceleration were solved. Figure 97–33 The engine had to be raised higher to get the new (noncollapsed) engine mount installed. The Vibrating Buick

Driveline “ clunk ” often occurs in rear-wheel-drive vehicles when shifting between drive and reverse or when accelerating from a stop. Often the cause of this noise is excessive clearance between the teeth of the ring and pinion in the differential. Another cause is called spline bind, where the changing rear pinion angle creates a binding in the spline when the rear springs change in height. When a pickup truck stops, the weight transfers toward the front and unloads the rear springs. The front of the differential noses downward and forward as the rear springs unload. When the driver accelerates forward, the rear of the truck squats downward, causing the drive shaft to be pulled rearward when the front of the differential rotates upward. This upward movement on the spline often causes the spline to bind and make a loud clunk when the bind is finally released. Spline Bind Cure - Part 1

The method recommended by vehicle manufacturers to eliminate this noise is to follow these steps: Spline Bind Cure - Part 2 Remove the driveshaft. Clean the splines on both the driveshaft yoke and the transmission output shaft. Remove any burrs on the splines with a small metal file (remove all filings). Apply a high-temperature grease to the spline teeth of the yoke. Apply grease to each spline, but do not fill the splines. Synthetic chassis grease is preferred because of its high temperature resistance. Reinstall the driveshaft.

PHOTO SEQUENCE Drive Axle Shaft Replacement Continued

PHOTO SEQUENCE Drive Axle Shaft ( cont. )

SUMMARY A defective U-joint often makes a clicking sound when the vehicle is driven in reverse. Severely defective U-joints can cause driveline vibrations or a clunk sound when the transmission is shifted from Reverse to Drive or from Drive to Reverse. Incorrect driveshaft working angles can result from collapsed engine or transmission mounts. Driveline clunk noise can often be corrected by applying high temperature chassis grease to the splines of the front yoke on the driveshaft. CV joints require careful cleaning, inspection, and lubrication with specific CV joint grease.

Chap97

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