Diagnosis Of Driveline Vibration (Road Test) - GMC G Service Manual

Figure 3 — Simple Universal Joint
DIAGNOSIS OF DRIVELINE VIBRATION
Four mayor component groups are usually the cause of
or are related to vibration. When a technician is road testing
a vehicle for vibration he must remember the four major
component groups:
1. Engine and mounts.
2. Clutch and transmission.
3. Tires, wheels and brake drums.
4. Propeller shaft and universal joints.
Before road testing a vehicle, check the following:
1. Propeller shaft is properly phased.
2. All fasteners for tightness at universal joints, wheel
studs and engine and transmission mounts.
3. Tire air pressure is correct.
4. Load conditions.
A. Ball Socket
(ROAD TEST)
ROAD TEST
A technician should road test the vehicle to diagnose
exactly what the complaint is. Record the speed and rpm at
which the greatest vibration occurs. The vibration is likely to
be in two places; in the steering wheel or in the seat bottom.
The road test can be helpful in locating the vibration source
either forward or aft.
COAST TEST
Drive the vehicle past the vibration speed, shift into neu­
tral, and coast back through the vibration speed. In this test
two kinds of vibration normally occur; a shaking or a buzz­
ing. A shaking vibration is usually tires or a wheel and brake
drum/disc assembly problem. A buzzing vibration is usually
a driveline problem.
PROPELLER SHAFT 4A-3
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Figure 4 — Constant Velocity Joint
B-06813