Driveline Systems

Driveline System

Special Tools:

Special Tool(s)

Inspection and Verification
Certain axle and driveline 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 concern 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.

Noise Acceptability
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.

Universal Joint (U-Joint) Inspection
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or seized U-joints. 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 vent.

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 mechanic's 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:
^ The seal is not correctly installed.
^ A 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 can be knocked out, which can 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.

A new pinion flange must be installed if any of these conditions exist.

Metal chips or sand trapped at the sealing lip can 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.

Analysis of Vibration

WARNING: An All-Wheel Drive (AWD) vehicle will always have all wheels (on both axles) driving. If only one wheel/axle is raised off the floor and the axle is driven by the engine, the wheel/axle on the floor could drive the vehicle off the stand or jack. Be sure all wheels are off the floor.

Few vibration conditions are caused by the front or rear axle. For a vibration concern, follow the diagnosis procedure unless there is a good reason to suspect the axle.

Tires

WARNING: Do not balance the wheels and tires while they are mounted on the vehicle. Possible tire disintegration or differential failure could result, causing personal injury or extensive component damage. Use an off-vehicle wheel and tire balancer only.

Most vibration is caused by tires, driveline angle or driveline imbalance.

Vibration is a concern with modern, high-mileage tires if they are not "true" both radially and laterally. They are more susceptible to vibration around the limits of radial and lateral runout of the tire and wheel assembly. They also require more accurate balancing. Wheel and tire runout checks, truing and balancing are normally done before axle inspection.

Driveline Imbalance
Driveline imbalance can be caused by excessive looseness in the driveshaft, damaged driveshaft tubing, looseness or high runout at the driveshaft attachments (axle and transfer case flanges). Excessive looseness in the driveshaft can be caused by CV joint or universal joint wear as well as loose fitting slip-yoke splines. Inspect and install new driveshaft components as necessary.

Driveline Angle








Driveline angularity is the angular relationship between the engine crankshaft, the driveshaft, and the rear axle pinion. Some of the factors determining driveline angularity include ride height, rear spring, and engine mounts.

Driveline Angle
An incorrect driveline (pinion) angle can often be detected by examining the driving condition in which the vibration occurs.
^ A vibration during coastdown from 72 to 56 km/h (45 to 35 mph) is often caused by an excessive U-joint angle at the axle (pinion nose downward).
^ A vibration during acceleration, from 56 to 72 km/h (35 to 45 mph) may indicate an excessive U-joint angle at the axle (pinion nose upward).

When these conditions exist, check the driveline angles.

1. CAUTION: Prior to checking driveline angularity, inspect the U-joints for correct operation.

Check the vehicle for evidence of overload or sagging. Check for specified air pressures in all four tires.
2. Normalize the suspension.
3. Drive the vehicle onto a drive-on hoist or front end alignment rack.





4. Inspect the suspension and chassis. Verify the vehicle curb position ride height is within specification.





5. Place the special tool on a clean, level section on the bottom of the frame. Press the ALT Zero button to calibrate the inclinometer to the vehicle.





6. For the driveshaft angle reading, place the special tool flush against the bottom of the driveshaft. Check and record the reading. Compare the results with the correct angles.





7. To check the pinion angle, rotate the driveshaft so the rear axle pinion flange yoke ear is parallel to the floor. Remove the U-joint snap ring and install the special tool. Check and record the pinion angle reading.
^ If the angle is not within specifications, inspect the rear suspension, rear axle, rear axle mounting or the frame for wear or damage. Repair or adjust to obtain correct angles.
8. To check the engine angle, rotate the driveshaft so the slip-yoke ear is parallel to the floor. Remove the U-joint snap ring and install the special tool. Check and record the engine angle reading.
^ If the angle is not within specifications, inspect the powertrain/drivetrain mounts or frame rails for wear or damage. Repair or adjust to obtain correct angles.
^ If the tires and driveline angle are not the cause, carry out the NVH tests to determine whether the concern is caused by a condition in the axle.

Universal Joint (U-Joint) Wear
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or seized U-joints. Install a new U-joint if it shows signs of seizure, excessive wear, or incorrect seating.

Wheel Hub Bolt Circle Runout

NOTE: The brake discs must be removed to carry out all runout measurements.





1. Position the special tool on the wheel hub bolt, as close to the hub face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub 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 bolt circle runout. The runout must not exceed 0.38 mm (0.015 inch).

Pilot Runout





1. Position the special tools on the pilot, as close to the hub as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub 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 Runout





1. Position the special tool on the wheel hub, as close to the outer edge as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub one full turn and note the maximum and minimum readings. The difference between the maximum and minimum readings will be the total wheel hub runout. The runout must not exceed 0.127 mm (0.005 inch).

Drive Pinion Stem and Pinion Flange
Check the pinion flange runout when all other checks have failed to show the cause of the 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.

Halfshafts

NOTE: Constant Velocity (CV) joints must not be installed unless disassembly and inspection reveals unusual wear.

NOTE: While inspecting the boots, watch 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 and wheel bearings as possible causes.

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 they are scored or damaged 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.

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.

On 4x4 vehicles, check the wheel bearing for rotating smoothness and end play.

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 (118 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, any other damaged parts in the axle housing must also be installed new.

Knock





Knock, which can occur in all driving phases, has several causes including damaged teeth or gearset.

1. NOTE: Measure the end play with a Dial Indicator with Bracketry and not by feel.

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 can 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 driveline angles which prevent the driveshaft slip-yoke from sliding on the output shaft. To correct this condition, lubricate the slip-yoke splines.

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.