GMC chervolet camaro 1999 Service Manual page 75

0-72 Vibration Diagnosis and Correction
Diagnosis and Repair of Engine Firing
Frequency-Related Vibrations
1. Raise and suitably support the vehicle. Refer to
Lifting and Jacking the Vehicle in General
Information.
Caution: Refer to Work Stall Test Caution in
Cautions and Notices.
2. Attempt to duplicate the vibration.
3. While the vibration is present, find the area of the
vehicle affected by the vibration.
4. Inspect for witness marks caused by rnbbing
components.
5. Isolate the component and re-evaluate the
vibration.
6. Inspect for proper torque on the affected
component. Tighten as needed.
7. If the vibration still exists, follow the
procedure below.
Engine Firing-Frequency Related Vibration
Causing Components
1. Inspect for collapsed engine mounts.
Replace as needed. Refer to Engine Mount
Replacement in Engine Mechanical - 3.8L or refer
to Engine Mount Replacement (Right) or
Engine Mount Replacement (Left) in Engine
Mechanical - 5.7L.
2. Inspect for collapsed or broken
transmission mount.
Replace as needed. Refer to Transmission Mount
in Transmission.
3. Inspect the exhaust hangers.
• Exhaust systems can expand one to two
inches when hot.
• Remove the hangers one at a time.
• Adjust or replace the exhaust hangers as
needed.
4. Inspect the A/C and P/S lines.
• Isolate the hoses from the body.
• Install the retainers.
5. Inspect the drive belt for the proper tension.
6. Inspect the accessory unit fasteners for damage
or looseness.
7. Inspect the body panels for missing or
loose welds.
8. Remove any aftermarket equipment that may
complete a transfer path into the passenger
compartment.
9. Inspect the exhaust system and powertrain
mounts. Re-bed the engine and align the exhaust
system as follows if needed:
• Loosen the mounts and hangers.
• Tighten all fasteners with the powertrain in the
relaxed position.
General Information
Some residual vibrations may be normal. Compare the
vibrations with a similar vehicle to get a feel for
what is commercially acceptable, preferably with the
customer present. Also, refer to bulletins for updates
on the use of mass damper weights for specific
applications.
Inherent Engine Shaking Forces
Just as with firing frequency, some engine
disturbances are the resul.t of normal operation. Some
engines can ·have additional inherent vibration due
to the cylinder arrangement, the design, or
the firing order.
Before attempting to repair a disturbance, compare
the disturbance to another, known good, vehicle. Some
vibrations could be normal though they may not be
pleasing to the customer.
The key to resolving an inherent engine disturbance is
to isolate the vibration from the passenger
compartment Follow the same procedures as outlined
for the engine firing-frequency related vibrations.
Engine-Driven Accessories
95613
Engine driven accessories that exhibit vibration pose
some special challenges. For example, the drive
belts can no longer be removed one at a time in order
to isolate the condition. If removing the belt eliminates
the vibration, reinstall the belt and operate each
accessory individually in order to determine which has
the most effect on the vibration. However, one
component may affect another because the drive belt
drives all of the accessories.
Verify that the accessory load is not affecting the
engine firing frequency.
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