GMC Chevrolet Camaro 1998 Service Manual page 66

0-54 Vibration Diagnosis and Corre.ction
Driveline vibrations may relate either to the first or to
the second order of driveline rotation. Driveline
vibrations are always related to the speed of the
vehicle. The vibration is often related to torque. If the
vibration is worse or only noticeable when
accelerating, decelerating, or crowding the throttle,
then the vibration is related to the torque. The vibration
will always occur at the same speed. If a vibration is
both torque and speed sensitive, the driveline is
the probable cause. Tire/wheel vibrations are speed
sensitive, but not torque sensitive.
First-Order Driveline Vibration Symptoms
The following symptoms may indicate first-order
driveline vibration:
• The vibration is related to vehicle speed.
• The vibration is torque sensitive.
• A "boom" or "moan" noise is present.
• The vibration occurs commonly above
72 km/h (45 mph), but possibly as low as
48 km/h (30 mph).
• The "roughness" or "buzz" vibration is felt in the
seat, floor or steering wheel.
• The corresponding frequency on the EVA equals
first-order driveline rotation (25-60 Hz), depending
on the speed of the vehicle and the .ratio of the
axle. Refer to the worksheet in order to obtain the
rotation speed of the propeller shaft.
Driveline Vibration Analysis
Once you identify a vibration that is related to the
driveline, continue testing in this service area.
The following components are possible sources of
first-order driveline vi.bration:
• The propeller shafts
• The transmission output shaft
• The pinion flange
• The pinion gear
General Information
Locate the Source of Driveline Vibration with
the EVA
Caution: Never run the vehicle faster than 112 km/h
(70 mph) when performing propeller shaft
vibration or checking for balance. Stay clear of
rotating components and balance weights to avoid
personal injury. Do not run the vehicle on the
hoist for extended periods of time to avoid engine
or transmission overheating. Do not step on the
brake pedal with the brake drums removed.
In order to pinpoint the source of vibration, reproduce
the vibration with the vehicle in the service stall.
Then determine which component is vibrating the most
using the EVA and the following procedure:
1. Raise the vehicle to curb height. Support the
vehicle on a hoist or on safety stands. Do not
allow the axle to hang. Refer to Lifting and Jacking
the Vehicle
2. Remove the rear tire/wheel assemblies. Refer to
Lifting and Jacking the Vehicle
3. Ensure that the propeller shaft is free of
undercoating.
4. Inspect the propeller shaft and U-joints for dents
or damage.
5. Start the engine.
6. Place the transmission in gear.
7. Run the vehicle at the speed which the vibration
occurs.
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Hold the EVA sensor against the pinion nose and the
transmission tailshaft assembly in order to determine
which end of the propeller shaft has the most vibration.
The end that has the most vibration will have a
higher amplitude on the EV A.
If the vehicle has a two-piece propeller shaft, inspect
the center support bearing.
If the transmission tailshaft vibrates, inspect the
transmission crossmember under the transmission
mount. If the mount is secured properly, there should
be no vibration at the crossmember.
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