GMC chevrolet camaro 2000 Service Manual page 57

0-46 Vibration Diagnosis and Correction
Depending on the symptoms or the frequency, the
repair will concentrate on one of the following
components:
.. The tire and wheel assemblies
" The transmission output shaft
.. The propeller shaft
• The rear. axle differential pinion
" The rear drive axle or the rear drive axle shafts
Downshift Test
Caution: Refer to Road Test Caution in Cautions
and Notices.
1. On a smooth, level road, accelerate to the speed
at which the concern vibration occurs.
Observe the engine RPM.
2. Decelerate and safely downshift to the next
lower gear.
3. Operate the vehicle at the previous engine RPM.
If the vibration returns at the same engine RPM,
the following conditions are the most probable causes
of the vibration:
.. The engine
" The clutch disc (manual transmission)
• The propeller shaft
• The transmission flywheel (automatic
transmission)
.. The torque converter
Repeat this test in lower gears, and in NEUTRAL, in
order to confirm the results.
In some cases, a vibration may also be sensitive to
torque or engine load, as well as being related to
a specific engine speed or vehicle speed. These
vibrations can be most difficult to diagnose, and require
additional testing. A systematic approach usually
leads to isolating the problem.
Neutral Run-Up Test
This test is designed to identify vibrations which are
related to the speed of the engine. Use this test when
the customer has a concern with vibration at idle,
or as a follow-up to the downshifttest. This test
probably doesn't apply when the complaint is related
to vehicle speed only (appearing at the same
vehicle speed regardless of the engine speed).
Caution: Refer to Road Test Caution in Cautions
and Notices.
1. Slowly increase the engine speed while looking
for disturbances that match the customer's
complaint.
2. Observe the engine speed (RPM) and the
frequency (if possible) where the vibration occurs.
General Information
Brake Torque Test
This test is designed to identify engine-related (
vibrations that were not uncovered with the neutral
run-up test. This test also works for vibrations that are
sensitive to the engine load or to the torque. This
test will probably not apply to vibrations which
are related only to the speed of the vehicle.
Caution: Refer to Road Test Caution in Cautions
and Notices.
i. Apply the park brake.
2. Block the front wheels.
3. Step firmly on the brake pedal.
4. Place the vehicle in DRIVE.
5. Slowly increase the engine speed while looking
for vibrations that match the customer's
description.
6. Observe the engine speed (RPM) and the
frequency (if possible) at which the disturbance
occurs.
7. If necessary, place the vehicle in REVERSE gear
and repeat steps 5 and 6.
Steering Input Test
This test is intended to determine how much the ·
wheel bearings and other suspension components
contribute to the vibration, especially a vibration · (.
relating to noise, such as growl, grinding, and roaring.
Caution: Refer to Road Test Caution in Cautions
and Notices.
1. With the vehicle at the vibration speed (mph),
drive through slow sweeping turns, first in
one direction and then in the other direction.
2. If the vibration gets worse or if the vibration goes
away, inspect the following components as
possible causes of the vibration:
• The wheel bearings
O
The hubs
• The tire tread
3. The CV joint angle increases when the vehicle is
turning. On front wheel drive (FWD) and
four wheel drive (4WD) vehicles, CV joint condition
systems may appear when the angle increases.
Putting a load on the CV joint may increase ·
the vibration amplitude. The third order, tire speed
related amplitude would remain the same. ·
(