GMC Chevrolet Camaro 1998 Service Manual page 71

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General Information
Isolating the Components
1. Perform the Neutral run-up test, noting the rpm at
which the vibration is the worst, and the severity.
Refer to Road Test.
2. Inspect all powertrain mounts. Repair or replace
as needed.
3. Inspect for any bindings or ground-outs in the
exhaust system.
Important: The following steps apply to A/T-equipped
vehicles only.
4. Matchmark the torque converter and the flywheel.
5. Disconnect the torque converter from the
propeller shaft, pushing the converter back from
the flywheel.
6. Tie up the converter, away from the flywheel.
7. Perform the Neutral run-up test again. Refer to
Road Test
• If the flexplate shows any wobble or lateral
runout, replace the flexplate. Refer to
Engine Flywheel Replacement or Engine
Flywheel Replacement
• Reindex the torque converter in three different
positions. If the disturbance still exists,
replace the torque converter.
8. If the vibration still exists, inspect the propeller
shaft runout.
9. If the vibration still exists, inspect the harmonic
balancer.
10. If the vibration still exists, the problem is related to
residual engine imbalance. Refer to the
procedure below.
Correcting Residual Engine Imbalance
1. Install washers on the harmonic balancer
pulley bolts.
2. Replace bolts with longer bolts of equal hardness
as needed.
3. (MIT only): Inspect the flywheel and the pressure
plate for the following conditions:
• Correct factory indexing. (The white paint spot
on the flywheel and the pressure plate should
line up.)
• Warping
• Balance
Vibration Diagnosis and Correction 0-59
Excessive Inherent Engine Firing Frequency
Engine Speeds and Frequencies
Firing
First Order Frequency
Type of
VS Fourth
Vibration rpm
Hz
Order
500 8.3 33.2
750 12.5
50.0
Shake
1000 16.6 66.4
1500
25.0 100.0
2000 33.3 133.2
Roughness
2500 41.6
166.4
3000 50.0 200.0
Buzz ··3500 110.6
233.2
4000 132.4 266.4
Firing frequency is a term used to describe the pulses
created as the engine fires each cylinder. All engines
have a firing frequency - but the object is to keep
these disturbances from entering the passenger
compartment. Initially, inspect for the following
conditions:
• The engine and the exhaust system are mounted
in a relaxed position. ·
• All of the mounts and hangers should be in good
condition and correct for the application.
• No components, hoses, or lines are grounding to
the frame or to the body.
The frequency of these disturbances will depend on
the number of cylinders. The engine order will always
be equal to one-half the number of cylinders. This
is because a four-stroke engine requires two complete
revolutions of the crankshaft in order to fire all of
the cylinders.
For example, a VB engine will fire cylinders 1, 3, 5,
and 7 on the first revolution. Cylinders 2, 4, 6,
and 8 will fire on the second revolution. This results in
four firing pulses per revolution of the crankshaft, or
fourth order.