Driveline Diagnosis and Service

1. Driveline Diagnosis and Service Chapter 76

2. Objectives • Diagnose and repair universal joints • Remove and replace axle bearings and seals • Disassemble and reassemble a differential • Run a gear pattern and adjust a differential

3. Introduction • Driveline components • Drive shaft and U-joints • Axles and axle bearings • Differential • This chapter covers more than driveline service and repair procedures • Hydraulic press procedures for installing bearings and other parts are described

4. Drive Shaft Diagnosis • Drive shaft problems result in noise or vibration • Worn or rusted U-joints • Worn slip yoke • Bad center support bearing • Causes of clunking sound when changing from acceleration to deceleration • Worn slip yoke splines • Bad extension housing bushing • Excessively worn U-joint • Problems in the differential

5. Drive Shaft Diagnosis (cont’d.) • Whining sound that varies with speed • Worn center support bearing in a two-piece driveshaft • Vibration • Bent driveshaft or a worn universal joint • Driveshaft inspection considerations • Physical damage and loose joints • Rust at seals • Excess slip yoke movement • Indentation in tubing

6. Universal Joint Diagnosis and Service • Universal joint begins to fail • Squeaking sound is often noticed • Most common cause of U-joint failure • Grease has dried out • Sharp, one-time click sound • Often occurs when vehicle direction is changed • Vibration can also occur

7. Drive Shaft Service • Steps to remove a drive shaft • Mark drive shaft • Unbolt rear U-joint from differential companion flange • Pry rear U-joint forward away from differential • Wrap tape around U-joint cups • On two-piece drive shaft: unbolt center support bearing • When removed: oil will come out of transmission

8. Universal Joint Disassembly • Important considerations • Remove any snap rings • There are three ways U-joints are commonly disassembled • Most common is to use a bench vise • Many shops have a special universal joint tool • Some shops pound the joint out with a hammer • Inspect the old U-joint for unusual wear • Problem with driveshaft angles can cause galling

9. Universal Joint Reassembly • Important steps and points • Replacement U-joints usually have a zerk fitting • If U-joint doesn't have zerk fitting: be sure to check that it has been packed with lubricant • Put bearing cup partially into yoke • Do not knock needle bearings out of position • Move joint back and forth to see that it is free • Install one snap ring before completing pressing procedure • Some replacement U-joints use internal snap rings

10. Drive Shaft Installation • Installing a drive shaft that bolts • Be sure universal joints fit exactly • Be sure all contact surfaces are clean • Major steps • With transmission in neutral: slip yoke into transmission • Align marks • Install rear U-Joint • Install retaining bolts

11. Two-Piece Drive Shaft Service • Center support bearing sometimes fails • Seized bearing can tear away rubber mount • Drive shaft will wobble • Bearing is pressed off and new one is pressed on • Be sure to press on the inside bearing race • Two pieces of drive shaft are separated • Reassemble in phase

12. Differential and Axle Diagnosis and Service • Differential gears on RWD • Rarely wear out • Causes of damage to gears • Moisture and dirt • Abuse by driver • Sometimes gear ratio change is desired • Requires disassembly

13. Problem Diagnosis • Important terms • Drive, cruise, coast, and float • Problems related to spider gears • Pinion gears too tight on shaft • Side gears too tight or too loose in differential case • Excessive backlash between spider gears • Lubricant leaks • Not usually an obvious problem

14. Axle Bearing Diagnosis • Damaged axle bearing • Can result in fluid leak or bearing noise • Important considerations • Driving the vehicle can sometimes pinpoint problem • Raise the vehicle after the road test • Have colleague run the engine with transmission engaged • Carrier bearings and pinion bearings will make a constant sound • Limited slip differentials can make a chattering sound during turns

15. Axle Bearing Service • Sealed rear axle bearings • No service interval • Axle removal is required • Presswork is usually done by parts business or machine shop • Repair of axle seal • Requires removal of axle from differential

16. Removing a Bearing-Retained Axle • Major steps and considerations • Remove retaining plate • Cover on back of differential must be removed prior to removal of a C-lock axle • Remove lock bolt of pinion shaft • Shaft is pulled out • Push axles inward • Allows C-locks to be removed • Pry out old seal and apply lubricant to new seal • Support the axle

17. Axle Bearing Replacement • Axles with pressed-fit bearings • Removed independent of backing plate • Pressed-fit bearing replacement • Do not try to press bearing and retaining ring off at same time • Bearing explodes during removal • Comparable to a grenade exploding

18. Axle Bearing Installationand Reinstall the Axle • Key points • Cage and rollers should always be able to be turned during installation • Retaining ring is often heated for easier assembly • Pressed into place against axle bearing • Reinstall axle in housing and bolt on retainer • Be sure that the slot in the retainer aligns with the oil return hole in the axle housing • Similar to oil return on clutch bearing retainer on a manual transmission

19. Full-Floating Axle Service • Found on trucks and vans • Three-quarter ton and larger • Axle bearings • Located in hub and brake drum assembly • Major steps • To remove drum: axle must be removed first • Install a new bearing seal • Retaining nut is tightened until it has little or no clearance • Install axle and beveled washers

20. Differential Pinion Seal Replacement • Important considerations • Maintain tension on pinion bearing crush sleeve • Use a dial indicator torque wrench • Always use a long bar to hold yoke from turning • Use puller to remove flange • Remove seal with hammer and chisel • Lubricate new seal and install

21. Differential Repair and Removing a Third Member • Identify differential • Look for an identification tag • Usually under one of the nuts holding third member or cover • Remove third member • Pull the axles • Remove all nuts from studs around third member • Remove washers • Be careful not to drop third member

22. Disassembling a Salisbury Axle • Major steps and considerations • Requires removal of rear cover • Remove C-locks and axles • Mark side bearing caps • Pry caps and remove from axle housing • Remove drive pinion gear

23. Clean and Inspect Parts • Considerations • Look for signs of wear • Keep bearing caps with their bearings

24. Differential Reassembly • Major steps and considerations • Clean and coat all parts with oil • Replace ring and pinion as a matched set • Install ring gears perfectly flat • Heat ring gear to make it easier to install • Torque ring gear retaining screws

25. Adjusting a Differential • Ring and pinion must mesh with each other in correct position • Incorrect position: noise and rapid wear may result • Adjustments • Pinion gear depth: measures how far the pinion gear extends into the differential housing • Ring and pinion backlash: too little backlash can break a gearset after it expands

26. Side Bearing Preload • Bearings can fail if too tight • Too loose: ring gear can move in case • Causes noise and wear • Salisbury axle preload and backlash adjustments • Made with shims • Installed by pounding them in • Separable third member • Side bearing adjustment made with backlash adjustment

27. Contact Pattern • Differential is adjusted • Gear pattern is taken off of ring gear teeth • Colored paste is painted onto gear teeth • Drive side of gear is convex • Coast side is concave • Pitch line • Runs through center of tooth • Face is area above pitch line and flank is area below • Good pattern • Tends to be toward the toe of tooth when tested

28. Backlash Pattern Change and Pinion Depth Pattern Change • An increased backlash causes pattern on both sides of gear tooth to move higher on tooth face • Moving ring gear closer to pinion will reduce backlash clearance • Altering pinion depth results in a different pattern change than changing backlash clearance • When changing pinion depth: leave pinion seal out until correct depth has been established

29. Pinion Bearing Preload and Ring and Pinion Noise • Pinion bearings must be preloaded • Use a collapsible spacer to preload the bearings • Check amount of effort required to turn pinion • Ring and pinion noise • Pattern is good but there is a gear howl • Replace ring and pinion • Noise during acceleration • Points to heavy heel contact • Noise happens when coasting in gear • Pattern will be too heavy on toe

30. Four-Wheel-Drive Service and Repair • Key points • Same as two-wheel-drive components except for transfer case and front hubs • Before attempting to service transfer case: check service manual • Mark both drive shafts at each end • Axles and locking hubs must be removed in order to remove differential from axle housing • 4WD wheel hub has a pair of tapered roller wheel bearings similar to those found on 2WD vehicles • 4WD axle is the same on inside as a 2WD axle