Component Tests and General Diagnostics
Driveline System
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.
Flex Coupling Inspection
Check for visible signs of tearing, cracking or wear in the reinforcing cord. If the flex couplings show signs of damage, inspect the axle and subframe mounts for cracking or tearing.
Driveshaft Center Bearing Universal Joint (U-Joint) Inspection
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or a seized U-joint. The U-joint is not repairable, a new driveshaft must be installed if the U-joint shows signs of seizure, excessive wear, or incorrect seating.
Driveshaft Center Bearing
Rotate the driveshaft by hand. If the bearing shows signs of roughness or is noisy, install a new bearing assembly.
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 halfshaft seals or differential seals.
^ Axle 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.
Flange Yoke Seal
Leaks at the axle drive pinion seal originate for the following reasons:
^ Seal is not correctly installed.
^ Damaged 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.
Differential Seals
Stub shaft pilot bearing housing seals are susceptible to the same kinds of damage as axle drive pinion seals if they are incorrectly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. The seal journal surface must be free of nicks, gouges and rough surface texture.
Analysis of Vibration
Few vibration conditions are caused by the rear axle. For a vibration concern, follow the diagnosis procedure in Noise, Vibration and Harshness Diagnosis 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 driveling 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, trueing 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. 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 operating angularity is the angular relationship between the input and output sides of any flex coupling or universal joint. Some of the factors determining driveling angularity inching ride height, rear spring, and engine mounts.
Driveline Operating Angle
NOTE: See Steps one through sixteen for front and rear flex coupling angles between joints one, two and three. Joint number one is the operating angle of the front flex coupler, number two is the operating angle of the center U-joint and number three is the operating angle of the rear flex coupler.
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 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 angle at the axle (pinion nose upward).
When these conditions exist, check the driveline operating angles.
1. CAUTION: Prior to checking driveling angularity, inspect the flex couplers and the U-joint for correct operation.
Check the vehicle for:
^ overload or sagging.
^ specified air pressures in all four tires.
^ loose axle mounts.
^ loose rear subframe-to-body mounts.
2. Normalize the suspension.
3. Drive the vehicle onto a drive-on hoist or front end alignment rack.
4. Inspect the suspension and chassis.
5. Remove the exhaust heat shield fasteners and slide the exhaust heat shield as far forward as possible to expose the driveshaft to axle flange coupling.
6. NOTE: The special tool contacts the flex coupling bolt sleeve to obtain an accurate reading. The bolt is serrated in the flange. The bolt should not be removed, only the nut.
Prepare to measure the front flex coupling operating angle (A).
1 Remove one of the nuts that attach the flex coupling to the transmission flange.
2 Install the special tool onto the bolt on the rear of the flex coupling and tighten the nut.
7. Place the special tool in the bracket slot with the special tool facing the passenger side and set the gauge to zero using the thumbscrew.
^ Remove the special tool and tighten the fastener to specification.
8. NOTE: The special tool must contact the flex coupling bolt sleeve to obtain an accurate reading. The bolt is serrated in the flange. The bolt should not be removed, only the nut.
Prepare to measure the front flex coupling operating angle (B).
1 Remove one of the nuts that attach the flex coupling to the front driveshaft.
2 Install the special tool onto the bolt on the front of the flex coupling and tighten the nut.
9. Place the special tool in the bracket slot with the special tool facing the passenger side and record the reading.
^ Remove the special tool and tighten the fastener to specification.
10. NOTE: The special tool must contact the flex coupling bolt sleeve to obtain an accurate reading. The bolt is serrated in the flange. The bolt should not be removed, only the nut.
Prepare to measure the rear flex coupling operating angle (C).
1 Remove one of the nuts that attach the flex coupling to the rear driveshaft.
2 Install the special tool onto the bolt on the rear of the flex coupling and tighten the nut.
11. Place the special tool in the bracket slot with the special tool facing the passenger side and record the reading.
^ Remove the special tools and tighten the fastener to specification.
12. NOTE: The special tool must contact the flex coupling bolt sleeve to obtain an accurate reading. The bolt is serrated in the flange. The bolt should not be removed, only the nut.
Prepare to measure the rear flex coupling operating angle (D).
1 Remove one of the nuts that attach the flex coupling to the pinion flange.
2 Install the special tool onto the bolt on the rear of the flex coupling and tighten the nut.
13. Place the special tool in the bracket slot with the special tool facing the passenger side and record the reading (D).
^ Remove the special tool and tighten the fastener to specification.
14. Calculate the operating angles of joints 1, 2 and 3 as follows:
^ A-B = Joint 1
^ B-C = Joint 2
^ C-D = Joint 3
15. NOTE: To adjust the center support bearing adjusting washers, the exhaust heat shield must be removed. Left and right washers should be the same thickness. Two washers should not be assembled together.
Adjust the joint operating angles by varying the center support bearing adjusting washers.
16. Install the exhaust heat shield.
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.
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: 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. Follow the diagnostic procedures in Noise, Vibration and Harshness Diagnosis.
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. Check the wheel bearing for a spelled cup, and spelled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.
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 badly damaged, 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 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 the speed of the driveshaft. Wheel bearing noise also may be high-pitched, similar to gear noise, but will be evident in all four driving modes.