GMC Chevrolet Camaro 1998 Service Manual page 68

0-56 Vibration Diagnosis and Correction
• The weight and original light spot are
90 to 180 degrees off (between the 9 and the
3 o'clock positions) - This condition means that
one weight is too much.
In order to correct the balance, split the two
weights equally on either side of the original light
spot. in order to produce a total weight less
than one (between 120 and 180 degrees apart).
Inspect the balance again using the strobe
light. Adjust the weights as necessary.
• The weight and the original light spot are
within 180 degrees of the 6 o'clock position.
Move weight towards the 6 o'clock position.
Inspect the balance again using the strobe light.
Adjust the weight as necessary. Refer to the
previous two conditions.
If the shaft will not balance using two weights, then
place a third weight on the light spot. Split the first
two weights in order to produce a total weight between
two and three weights.
If three weights fail to balance the driveline, replace
the propeller shaft.
When the propeller shaft balances, road test the
vehicle in order to verify that the vibration is eliminated.
First-Order Driveline Vibration Analysis
(Torque Sensitive)
If the vehicle has a vibration that is equal to first-order
driveline rotation, and the vibration is not present
when testing the vehicle in the stall, then internal rear
axle components are the probable cause of the
vibration.
Internal rear axle components are also the probable
cause of the vibration if you were able to correct
the vibration in the stall, but the vibration returned
during the road test. Internal rear axle vibrations may
be aggravated by the load of the vehicle working
against the ring and pinion gear seat.
Since the propeller shaft and the pinion gear are
bolted together through the pinion flange, the propeller
shaft and the pinion gear operate at the same
speed. Vibration in the pinion gear will therefore have
the same frequency and symptoms as the
propeller shaft.
In order to isolate the vibration to the pinion gear, use
the following procedure:
1 . Raise the vehicle to curb height. Support the
vehicle on a hoist or on safety stands. Refer
to Lifting and Jacking the Vehicle in General
Information.
2. Remove the tire/wheelassemblies. Refer to
Wheel Removal in Tires and Wheels.
3. Remove the brake drums.
4. Touch the pinion nose, or hold the EVA vibration
sensor up to the pinion nose.
General Information
5. Use another technician in order to accelerate' and
decelerate the vehicle through the speed range at
which the vibration was noticed during the
road test.
Example
• If the vibration was originally noticed at
88 km/h (55 mph), accelerate from 72 km/h
(45 mph) to 107 km/h (65 mph). Then
decelerate from 107 km/h (65 mph) back to
72 km/h (45mph).
• Repeat the above step and note whether or
not the pinion nose vibrates under load
during acceleration and/or deceleration.
If the vibration does not occur during the above
procedure, install the brake drums and the tire/wheel
assemblies. The brake drums and tire/wheel
assemblies will add additional load on the system.
Then repeat the above test.
Ensure that t>oth axle shafts rotate at the same speed.
The differential may mask a vibration when one tire
is spinning faster than the other tire. Adjust the brakes
in order to correct ynequal tire rotation speed.
If you are unable to reproduce the vibration in the
stall, apply the brake lightly in order to load the system
further. Maintain the vehicle speed at which the
vibration was noticed. Do not overheat the brakes.
If the pinion nose vibrates under acceleration and/or
deceleration, and the ottier driveline components
are eliminated as the cause of the vibration, then one
of the following conditions may cause the vibration:
• A high spot on the pinion gear
• A bent pinion stem
• A cocked pinion bearing
• An improper axle housing bore
Anything that effects the pinion gear and how the
pinion gear contacts. the rotating ring gear may
contribute to a first-order, torque-sensitive driveline
vibration. The only way to correct the condition
is to replace the faulty components. In most cases,
the ring and piniori gear set and the related bearings
must be replaced. In some case, however, the
axle housing must be replaced .. Complete a close-up
visual inspection for damage or unusual wear in
order to measure or identify the specific faulty
component.
It is possible to isolate an internal axle vibration. Install
a "known good" axle assembly from a stock unit.
Verify that the "known good" axle assembly does not
have a vibration problem.
Once you correct the internal axle problem, road test
the vehicle. Inspect the vehicle for vibration.
Balance the driveline as necessary in order to
eliminate any remaining vibration.
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