GMC chervolet camaro 1999 Service Manual page 439

4-24 Rear Drive Axle
7. Determine if loose or rough front wheel inner or
outer bearings cause the noise.
• Noise in front wheel inner or outer bearings
does not change between drive and coast.
• Light application of the brake pedal while
holding the vehicle speed steady takes
some weight off of the bearings. This action
will often cause noise in front wheel inner
or outer bearings to diminish.
• Use the following steps in order to determine if
the front wheel inner and outer bearings
are loose:
7.1. Jack up the tires and the wheels.
7.2. Spin or shake the tires and the
wheels in order to determine if the
bearings are loose.
8. Rear axle noise is dampened when the rear
suspension rubber bushings and the spring
insulators are correctly installed.
Determine if any metallic contact exists between
the following components:
• The spring and the spring opening in the
underbody
• The lower control arm bushings and the
underbody or axle housing brackets
Metal-to-metal contact at these points may
increase road noise and normal axle noise.
Rear Axle Noises
After verifying that a noise exists in the rear axle,
determine the type of the noise. Determining the type
of the rear axle noise will aid in repair.
Gear Noise
Gear noise (whine) is audible from 32-89 km/h
(20-55 mph) under the following driving conditions:
• Drive - Acceleration or heavy pull
• Road Load - The vehicle driving load or the
constant speed
• Float - Using enough throttle in order to keep the
vehicle from driving the engine, the vehicle slows
down gradually but the engine still pulls slightly.
• Coast - The throttle closes and the vehicle is
in gear.
Gear noise is most noticeable when the vehicle is
operating at the following speeds:
- 64-80 km/h (40-50 mph)
- 97-105
km/h
(60-65
mph)
Drive line/ Axle
Bearing Noise
Poor bearings generally produce a rough growl or
grating sound, rather than the whine typical of
gear noise.
Bearing noise frequently "wow-wows" at constant
RPMs. This noise may indicate that the following
components are faulty:
• The differential drive pinion gear
• The side bearings
The ''wow-wow" bearing noise may be confused with
rear wheel bearing noise. Inspect and replace as
necessary.
Rear Wheel Bearing Noise
The noise that is produced by a rough rear wheel
bearing is evident under the following conditions:
• The vehicle is coasting at low speeds
• The transmission range selector lever is in
NEUTRAL
The bearing noise may diminish with gentle braking.
Use the following steps in order to determine if a noise
is caused by a rough rear wheel bearing:
1. Raise the rear tires and wheels.
2. Spin the rear tires and wheel by hand.
3. Listen at the hubs for evidence of rough (noisy)
rear wheel bearings.
Knock At Low Speeds
One of the following conditions may cause a knock at
low speeds:
• A worn universal joint
• A worn or oversized side gear hub counterbore in
the differential case
Inspect and replace the above components as
necessary.
Backlash Clunk
One of the following conditions may cause excessive
backlash clunk with acceleration and deceleration:
• A worn differential drive pinion gear shaft
• A worn differential case
• Excessive clearance between· the following
components:
- The rear axle shaft splines and the side gear
splines
- The side gear hub and the counterbore in
the case
• A worn differential drive pinion gear and worn side
gear teeth
• Worn differential pinion gear thrust washers
• Excessive differential ring gear-to-differential drive
pinion gear backlash
Replace the worn components as necessary. Select
close fitting replacement parts.
Adjust the differential ring gear-to-differential drive
pinion gear backlash. Refer to Backlash Adjustment
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