Driveline System - General Information
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Special Tool(s)
Inspection and Verification
Certain axle noise or vibration symptoms are also common to the engine, transmission, wheel bearings, tires, and other parts of the vehicle. For this reason, be sure that the cause of the trouble is in the axle before disassembling, adjusting or repairing the axle.
Certain driveshaft vibration symptoms are common to the front engine accessory drive (FEAD), the engine, transmission or tires. Be sure the cause of the concern is the driveshaft before repairing or installing a new driveshaft.
Certain symptoms may be caused by Traction-Lok differentials. Check the vehicle certification label and axle identification tag to determine the type of differential.
Noise Acceptability
NOTE: A gear-driven unit will produce a certain amount of noise. Some noise is acceptable and audible at certain speeds or under various driving conditions such as a newly paved blacktop road. Slight noise is not detrimental to the operation of the axle and is considered normal.
With the Traction-Lok differential axle, slight chatter noise on slow turns after extended highway driving is considered acceptable and has no detrimental effect on the locking axle function.
Universal Joint (U-Joint) Inspection
WARNING: The electrical power to the air suspension system must be shut off prior to hoisting, jacking or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch. Failure to do so can result in unexpected inflation or deflation of the air springs, which can result in shifting of the vehicle during these operations.
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or seized U-joint. Install a new U-joint if it shows signs of seizure, excessive wear, or incorrect seating.
Analysis of Leakage
Clean up the leaking area enough to identify the exact source. An axle leak can be caused by the following:
^ Axle lubricant level is too high
^ Worn or damaged axle shaft seals or differential seals.
^ Differential housing is cracked.
^ Flange yoke seal is worn or damaged.
^ Pinion flange is scored or damaged.
^ Axle cover is not sealed.
^ Vent is plugged.
Repair the axle as necessary. Make sure the axle lubricant is at the correct level.
Axle Vent
NOTE: If a plugged vent cannot be cleared. install a new one.
A plugged vent will cause excessive seal lip wear due to internal pressure buildup. If a leak occurs, check the vent. Make sure the vent hose is not kinked. Remove the hose from the vent nipple and clear the hose of any foreign material. While the hose is removed, pass a length of mechanics wire or a small diameter Allen wrench in and out of the vent to clean it. Connect the hose when done.
Flange Yoke Seal
Leaks at the axle drive pinion seal originate for the following reasons:
^ Seal was not correctly installed.
^ Poor quality seal journal surface.
Any damage to the seal bore (dings, dents, gouges, or other imperfections) will distort the seal casing and allow leakage past the outer edge of the axle drive pinion seal.
The axle drive pinion seal can be torn, cut, or gouged if it is not installed carefully. The spring that holds the axle drive pinion seal against the pinion flange may be knocked out and allow leakage past the lip.
The rubber lips can occasionally become hard (like plastic) with cracks at the oil lip contact point. The contact point on the pinion flange may blacken, indicating excessive heat. Marks, nicks, gouges, or rough surface texture on the seal journal of the pinion flange will also cause leaks.
Axle drive pinion seal wear 1.27 mm (0.050 inch) or greater is considered excessive.
A new pinion flange must be installed if any of these conditions exist.
Metal chips or sand trapped at the sealing lip may also cause oil leaks. This can cause a wear groove on the pinion flange and heavy pinion seal wear.
When a seal leak occurs, install a new seal and check the vent and the vent hose to make sure they are clean and free of foreign material.
Axle Shaft Seals
Axle shaft oil seals are susceptible to the same kinds of damage as axle drive pinion seals if incorrectly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. Axle shaft journal surface must be free of nicks, gouges, and rough surface texture.
Analysis of Vibration
WARNING: A vehicle equipped with a Traction-Lok differential will always have both wheels driving. If only one wheel is raised off the floor and the rear axle is driven by the engine, the wheel on the floor could drive the vehicle off the stand or jack. Be sure both rear wheels are off the floor.
Few vibration conditions are caused by the front or rear axle. On a vibration concern, follow the diagnosis procedure unless there is a good reason to suspect the axle.
Wheel Hub or Axle Flange Bolt Circle Runout
NOTE: The brake discs must be removed to carry out all runout measurements.
1. Position the special tool perpendicular to the wheel hub or axle flange bolt, as close to the hub or flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub or flange until the next bolt is contacted. Record the measurement and continue until each bolt is checked. The difference between the maximum and minimum contact readings will be the total wheel hub or axle flange bolt pattern runout. The runout must not exceed 0.38 mm (0.015 inch).
Pilot Runout
1. Position the special tool as close to the hub or axle flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub or flange one full turn and note the maximum and minimum readings. The difference between the maximum and minimum readings will be the total pilot runout. Pilot runout must not exceed 0.15 mm (0.006 inch).
Wheel Hub or Axle Flange Face Runout
NOTE: If the axle shaft assembly is removed, check runout of the shaft itself. The forged (unmachined) part of the shaft is allowed to have as much as 3.0 mm (0.120 inch) runout. This alone will not cause a vibration condition.
1. Position the special tools on the wheel hub or axle flange face, as close to the outer edge as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub or flange one full turn and note the maximum and minimum readings. The difference between the maximum and minimum readings will be the total face runout. The runout must not exceed 0.254 mm (0.010 inch).
Drive Pinion Stem and Pinion Flange
Check the pinion flange runout when all other checks have failed to show the cause of vibration.
One cause of excessive pinion flange runout is incorrect installation of the axle drive pinion seal. Check to see if the spring on the seal lip has been dislodged before installing a new ring gear and pinion.
Halfshafts
NOTE: New constant velocity (CV) joints must not be installed unless disassembly and inspection reveals unusual wear.
NOTE: Inspect the boots for indentations ("dimples") in the boot convolutions. Indentations must be removed.
^ Inspect the boots for evidence of cracks, tears, or splits.
^ Inspect the underbody for any indication of grease splatter near the boots outboard and inboard locations. This is an indication of boot/clamp damage.
Axle Noise
NOTE: Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks, axle shafts and wheel bearings as possible causes. Follow the diagnostic procedures.
The noises described as follows usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are the type of noise heard during the road test.
Gear Howl and Whine Howling or whining of the ring gear and pinion is due to an incorrect gear pattern, gear damage or incorrect bearing preload.
Bearing Whine
Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by worn/damaged pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds.
This distinguishes it from gear whine which usually comes and goes as speed changes.
As noted, pinion bearings make a high-pitched, whistling noise, usually at all speeds. If however there is only one pinion bearing that is worn/damaged, the noise may vary in different driving phases. New pinion bearings must not be installed unless scoring or damage is found or there is a specific pinion bearing noise. A worn/damaged bearing will normally be obvious at disassembly. Examine the large end of the rollers for wear. If the pinion bearings original blend radius has worn to a sharp edge, a new pinion bearing must be installed.
NOTE: A low-pitched rumble normally associated with a worn/damaged wheel bearing can be caused by the exterior luggage rack or tires.
A wheel bearing noise can be mistaken for a pinion bearing noise. On 4x2 vehicles, check the wheel bearing for a spelled cup, and spelled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.
If the wheel bearing is damaged, the roller surface on the axle shaft may also be damaged. Install a new axle shaft if any damage is detected.
On 4x4 vehicles, check the wheel bearing for rotating smoothness and end play. Install new wheel bearings as required.
Chuckle
Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the differential gear hub and the differential case bore.
Damage to a gear tooth on the coast side can cause a noise identical to a chuckle. A very small tooth nick or ridge on the edge of a tooth can cause the noise.
Clean the gear tooth nick or ridge with a small grinding wheel. If the damaged area is larger than 3.2 mm (1/8 inch), install a new gearset.
To check the ring gear and pinion, remove as much lubricant as possible from the gears with clean solvent. Wipe the gears dry or blow them dry with compressed air. Look for scored or damaged teeth. Also look for cracks or other damage.
If either gear is scored or damaged badly, a new ring gear and pinion must be installed.
If metal has broken loose, the axle housing must be cleaned to remove particles that will cause damage. At this time if any other damaged parts are found in the axle housing, new parts must also be installed.
Knock
Knock, which can occur on all driving phases, has several causes including damaged teeth or gearset.
In most cases, one of the following conditions will occur:
1. A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.
2. NOTE: Measure the end play with a Dial Indicator Gauge with Holding Fixture and not by feel.
The knock is also caused by excessive end play in the axle shafts. Up to 0.762 mm (0.030 inch) is allowed in semi-float axles. The frequency of the knock will be less because the axle shaft speed is slower than the driveshaft.
Clunk
Clunk is a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE. The noise may also occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components; it is felt or heard in the axle.
Additionally, clunk may be heard upon initial drive-away. This occurs as engine torque shifts vehicle weight, forcing changes in driveling angles, preventing the driveshaft slip-yoke from sliding on the output shaft. To correct this condition, lubricate the slip-yoke splines.
Total Backlash Check
WARNING: The electrical power to the air suspension system must he shut off prior to hoisting, jacking or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch. Failure to do so can result in unexpected inflation or deflation of the air springs, which can result in shifting of the vehicle during these operations.
1. Raise and support the vehicle.
2. Remove the driveshaft.
3. Install the special tool.
^ Clamp a rigid bar or pipe to the tool. Clamp the other end of the bar or pipe to the flame or a body member in order to prevent movement of the pinion flange.
4. Lower the vehicle so that one rear wheel is resting on a wheel chock to prevent it irons turning. The other rear wheel will be used to measure total rear axle backlash.
5. Rotate the free wheel slowly, by hand, until the feeling of driving the rear axle is encountered. Place a mark on the side of the tire, 305 mm (12 inches) from the center of the wheel. with a crayon or chalk.
6. While holding the crayon or chalk against the tire, rotate the wheel slowly in the opposite direction until the feeling of driving the rear axle is encountered again.
7. Measure the length of the crayon or chalk mark on the tire.
^ If the length of the mark is 25.4 mm (1 inch) or less, the rear axle backlash is within allowable limits.
^ If the chalk mark is greater than 25.4 mm (1 inch), check for these conditions:
- Elongation of the differential pinion shaft and holes in the differential case.
- Missing differential pinion thrust washer or differential side gear thrust washer
- alling of the differential pinion shaft and bore.
- Excessive ring gear and pinion backlash. Follow the procedure for the type of rear axle to check backlash.
Axle Shaft Bearing Noise
Axle shaft bearing noise is similar to gear noise and differential pinion bearing whine. Axle shaft bearing noise will usually distinguish itself from gear noise by occurring in all driving modes (drive, coast, and float), and will persist with the transmission in NEUTRAL while the vehicle is moving at the speed in which the concern is occurring. If the vehicle makes this noise, remove the suspect axle shaft and install a new bearing and axle seal. Re-evaluate the vehicle for noise before removing any internal components.
Bearing Rumble
Bearing rumble sounds like marbles being tumbled.
This condition is usually caused by a worn/damaged wheel bearing. The lower pitch is because the wheel bearing turns at only about one-third of the driveshaft speed. Wheel bearing noise also may be high-pitched, similar to gear noise, but will be evident in all four driving modes.