Flow of Diagnosis

NOTE: A successful failure analysis requires three steps:
- Identify the type of failure.
- Determine the cause of the failure.
- Take corrective action to prevent a recurrence.

DESCRIPTION
Certain rear axle and driveline concerns are also common to the engine, transmission, wheel bearings, tires and other parts of the vehicle. For this reason make sure the cause of the trouble is in the rear axle before adjusting, servicing or replacing any of the parts. Rear axle concerns can be diagnosed and corrected quickly by following the proper procedures. Being able to perform a good diagnosis is necessary in order to eliminate guesswork and save time. These tests define various possible rear axle conditions and tests for identifying the cause and the service procedure. The four rear axle conditions that will be reviewed are:
1. Leakage conditions:
a. rear axle drive pinion seal
b. drive pinion nut
c. inner wheel bearing oil seals
d. casting porosity weld leaks rear axle housing vent
2. Vibration conditions:
a. tires
b. driveline angle
c. axle shaft runout
d. drive pinion stem and rear axle universal joint flange
3. Noise conditions:
a. non-axle noise
b. axle noise:
(1) gear noise
(2) chuckle
(3) knock
(4) clunk
(5) bearing whine
(6) chatter on corners
(7) click at engagement
(8) axle shaft noise
c. bearing rumble
4. Inoperative conditions:
a. Broken pinion stem
b. Broken welds
c. Wheel bearing malfunctions
d. Axle lockup
The diagnostic material also deals with symptom analysis which aids the technician in discovering the original cause of a concern so repeat service can be avoided.

QUESTION THE CUSTOMER
1. The preliminary diagnosis begins with the service technician asking the customer enough diagnostic questions, especially those indicating conditions of noisy operation or vibration. Always ask the customer about:
- The exact nature of the symptom. If it is a vibration how is it felt? If a noise, what kind? Is it high-pitched, a rumbling noise or some other concern?
- The driving conditions in which the symptoms appear: road speed, drive or coast, on turns or on a grade only.
- Whether the condition is constant or variable. Does a noise increase in pitch with speed or some other factor?
2. All information should be written on the service order so the technician will know where to start looking. The technician doing the diagnosis must be able to identify the axle concern from what is written on the service order following the road test.
3. Have the customer demonstrate the symptoms in a road test whenever possible.

AXLE DIAGNOSIS CHECK SHEET
1. If there is enough reason to suspect an axle concern, the service technician should also initiate a customer concern evaluation. Record all the information related to the concern in order to diagnose it accurately and quickly.
2. After gathering the necessary information, begin with a road test.