Drive/Propeller Shafts, Bearings and Joints: Testing and Inspection
SYMPTOM TROUBLESHOOTING CHART - DRIVELINE / AXLEPreliminary Diagnosis
^ Question the Customer
The preliminary diagnosis starts with the customer interview. The history of the concern must be investigated: When was it first noticed? Did it appear suddenly or gradually? Did any abnormal occurrence coincide with or precede its appearance (such as pothole or curb impacts, minor collisions, etc.)? Were any repair procedures performed or parts replaced? It is also necessary to know any special conditions affecting the appearance and degree of the concern, such as road speed, type of road, drive mode, engine temperature, ambient temperature, etc.
A gradual appearance of the concern indicates a deterioration of a component, such as tires, halfshafts or front wheel bearings.
A sudden appearance of the concern could indicate a lost wheel balance weight or frozen constant velocity (CV) joint.
ROAD TEST - DRIVELINE / AXLE
A road test is mandatory for any customer concern of noise/vibration that is not verified by the on-hoist check of chassis components.
Operate the vehicle in all four modes and record those in which the noise occurs. Write down the kilometers-per-hour (miles-per-hour) range at which both noise and vibration occur. Evaluate rear axle noise with the transmission in DIRECT DRIVE and not in OVERDRIVE. Transmission noise can be mistaken for rear axle noise when in OVERDRIVE.
AXLE 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 chaffer noise on slow turns after extended highway driving is considered acceptable and has no detrimental effect on the locking axle function.
PROPELLER SHAFT 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 trouble is in the axle before adjusting, repairing, or replacing any of its parts.
Certain symptoms may be caused by limited slip differentials. Check the vehicle certification label and axle identification tag to determine the type of differential.
AXLE - 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 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 if necessary.
Make sure the axle lubricant it, at the proper level.
AXLE VENT
Note:
^ If the vent cannot be cleared, it must be replaced.
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.
AXLE DRIVE PINION SEAL
Leaks at the axle drive pinion oil seal originate for the following reasons:
^ Seal was not properly 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 companion 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 companion flange may blacken, indicating excessive heat. Marks, nicks, gouges, or rough surface texture on the seal journal of the companion flange will also cause leaks.
Axle drive pinion seal wear 1.27 mm (0.050 inch) or greater is considered excessive.
The companion flange must be replaced 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 companion flange and heavy pinion seal wear.
When a seal leak occurs, replace the seal and check the vent and the vent hose to make sure they are clean and free of debris.
DRIVE PINION NUT
Caution:
^ Be sure to follow the correct procedure for setting the bearing preload when the nut is installed.
On some high-mileage units, oil may leak past the threads of the pinion nut. This condition can be corrected by removing the nut and applying sealant on the threads and nut face.
AXLE SHAFT SEALS
Axle shaft oil seals are susceptible to the same kinds of damage as axle drive pinion seals if improperly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. The axle shaft journal surface must be free of nicks, gouges, and rough surface texture.
DIFFERENTIAL SEALS
For additional information on differential seals, see AXLE AND DIFFERENTIAL STRUCTURAL VIEW REAR (LIMITED SLIP), or See AXLE AND DIFFERENTIAL STRUCTURAL VIEW REAR (STANDARD), for the rear axle or See AXLE AND DIFFERENTIAL FRONT DISASSEMBLY / ASSEMBLY, for the front axle.
DRIVELINE / AXLE VIBRATION ANALYSIS
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. Failure to follow these instructions may result in personal injury.
Few vibration conditions are caused by the front or rear axle. On a vibration concern, follow the diagnosis procedure in SYMPTOM TROUBLESHOOTING CHART - DRIVELINE / AXLE, unless there is a good reason to suspect the axle. Symptom Troubleshooting Chart - Driveline / Axle
TIRES
Warning:
^ Do not balance the wheels and tires while they are mounted on the vehicle. Possible tire disintegration/ differential failure could result, causing personal injury/extensive component damage. Use an off- vehicle wheel and tire balancer only.
Most vibration in the rear end is caused by tires or driveline angle.
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 ANGLE
Driveline angularity is the angular relationship between the engine crankshaft, the propeller shaft, and the rear axle pinion, Factors determining driveline angularity include ride height, rear spring, and engine mounts.
Driveline Angle
An incorrect driveline (pinion) angle can often be detected by 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.
If the tires and driveline angle are not the cause, perform the NVH tests to determine whether the concern is caused by a condition in the axle.