Chevrolet Silverado / GMC Sierra. Service manual — part 1399

Locking Rear Axle Does Not Lock

Locking Rear Axle Locks in Turns

Locking Rear Drive Axle Chatters in Turns

Noise in Addition to Normal Clutch Engagement

SYMPTOMS - REAR DRIVE AXLE

Review the system and operation in order to familiarize yourself with the system functions. Refer
to Rear Drive Axle Description and Operation.

Rear Axle Noise

The proper diagnosis is an important part of rear axle repair. In axle work, one of the most
difficult conditions to diagnose is noise. Locating a broken axle shaft or broken differential gear
presents little or no problems, but locating and isolating axle noise can be an entirely different
matter.

Any gear driven unit, especially an automotive drive axle where the engine torque multiplication
occurs at a 90 degree turn in the driveline, produces a certain amount of noise. Therefore, an
interpretation must be made for each vehicle in order to determine where the noise is normal or if
a problem actually exists. A certain amount of noise must be expected and cannot be eliminated
by conventional repairs or adjustment.

Normal axle noise can be described as a slight noise heard only at a certain speed or under
unusual or remote conditions. For example, the noise tends to reach a peak at speeds from 60-100
km/h (40-60 mph) depending on road and load conditions, or on gear ratio and tire size. This
slight noise is in no way indicative of trouble in the axle assembly.

Driveline noises may confuse even the best technician. Vehicle noises coming from tires,
transmission, propeller shaft, universal joints, and front or rear wheel bearings are often mistaken
for axle noise.

Visual/Physical Inspection

Inspect the system for loose or missing fasteners.

Inspect the system for leaking components.

Inspect the system for obvious damage or conditions which may cause the symptom.

Symptom List

Refer to a system diagnostic procedure from the following list in order to diagnose the symptom:

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Rear Drive Axle Noises

Noisy in Drive

Noisy When Coasting

Intermittent Noise

Constant Noise

Noisy on Turns

REAR DRIVE AXLE NOISES

Gear Noise

Gear noise or whine is audible from 32-89 km/h (20-55 mph) under 4 driving conditions:

Drive- Acceleration or heavy pull

Road Load-Vehicle driving load or constant speed

Float-Using enough throttle to keep the vehicle from driving the engine, the vehicle slows
down gradually but the engine still pulls slightly

Coast-Throttle is closed and the vehicle is in gear

Gear noise most frequently has periods where the noise is more prominent, usually between 48-64
km/h (30-40 mph) and 80-85 km/h (50-53 mph). Gear whine is corrected by either ring and
pinion gear replacement or adjustment, depending on the mileage of the gearset.

Bearing Noise

Faulty bearings produce a rough growl or grating sound, rather than the whine typical of gear
noise. Bearing noise/hum will pulsate at a constant vehicle speed. This indicates a bad pinion or a
bad rear axle side bearing. This noise can be confused with rear wheel bearing noise. Inspect and
replace the bearings and the affected components as required.

Rear Wheel Bearing Noise

A rough rear wheel bearing produces a noise which continues with the car coasting at low speed
and the transmission in neutral. The noise may diminish some when the brakes are gently applied.
The noise may also change when performing side-to-side maneuvers with the vehicle.

A rough/noisy rear wheel bearing can be heard by spinning the rear wheels by hand and listening
at the hubs for the noise. Inspect and replace the bearings and the affected components as needed.

Knock at Low Speeds

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

A low speed knock can be caused by a differential case side gear bore that has worn oversize.
Inspect the side gears and differential case and replace the components as necessary.

Backlash Clunk

Excessive backlash clunk under acceleration or deacceleration can be caused by any of the
following:

Worn differential pinion shaft

Worn differential pinion and/or side gear teeth

Worn thrust washers

Excessive clearance between the side gears and the axle shafts

Excessive clearance between differential side gears and the bore in the case

Excessive drive pinon and ring gear backlash

Inspect, adjust or replace the affected components as necessary.

NOISY IN DRIVE

Cause

Correction

DEFINITION: A noise heard during acceleration load.
Excessive pinion to ring gear
backlash

Adjust the pinion to ring gear backlash. Refer to Backlash
Adjustment (8.6 Inch Axle) or Backlash Adjustment
(10.5, 11.5 Inch Axles) or Backlash Adjustment (9.5 LD
Axle).

Worn pinion and ring gear

Replace the pinion and the ring gear. Refer to Drive Pinion
and Ring Gear Replacement (8.6, 9.5/9.5LD, and 11.5
Inch Axles) or Drive Pinion and Ring Gear Replacement
(10.5 Inch Axle).

Worn pinion bearings

Replace the pinion bearings. Refer to Drive Pinion Bearings
Replacement (8.6, 9.5, 11.5 Inch Axle) or Drive Pinion
Bearings Replacement (10.5 Inch Axle).

Loose pinion bearings

Adjust the pinion bearings preload. Refer to Pinion Depth
Adjustment (10.5 Inch Axle) or Pinion Depth Adjustment
(8.6, 9.5/9.5LD, and 11.5 Inch Axles).

Excessive pinion end play

Adjust the pinion end play. Refer to Pinion Depth
Adjustment (10.5 Inch Axle) or Pinion Depth Adjustment
(8.6, 9.5/9.5LD, and 11.5 Inch Axles).

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

NOISY WHEN COASTING

INTERMITTENT NOISE

Worn differential bearings

Replace the differential bearings. Refer to Differential Side
Bearings Replacement (All Except 9.75 Inch Axle).

Loose differential bearings

Adjust the differential bearing preload. Refer to Differential
Carrier Bearing Preload Adjustment (10.5 Inch, 11.5
Inch Axles) or Differential Carrier Bearing Preload
Adjustment (8.6 Inch Axle) or Differential Carrier
Bearing Preload Adjustment (9.5, and 9.5LD Inch Axles).

Excessive ring gear runout

Replace the ring gear. Refer to Drive Pinion and Ring Gear
Replacement (8.6, 9.5/9.5LD, and 11.5 Inch Axles) or

Drive Pinion and Ring Gear Replacement (10.5 Inch
Axle)

.

Low oil level

Fill the fluid level to specifications with the proper lubricant.
Refer to Rear Axle Lubricant Level Inspection (11.5 Inch
Axle) or Rear Axle Lubricant Level Inspection (8.6, 9.5
LD Axle) or Rear Axle Lubricant Level Inspection (10.5
Inch Axle).

Wrong or poor grade oil

Drain and refill the system with the proper lubricant. Refer to
Rear Axle Lubricant Replacement (8.6 Inch Axle) or

Rear Axle Lubricant Replacement (9.5 Inch LD Axle)

or

Rear Axle Lubricant Replacement (10.5 Inch Axle).

Bent axle housing

Replace the axle housing. Refer to Rear Axle Housing
Replacement (w/Rear Drum) or Rear Axle Housing
Replacement (w/Rear Disc ).

Checks

Action

DEFINITION: Noise is audible when slowing down and disappears when driving.
Worn pinion and ring gear

Adjust or replace the pinion and the ring gear. Refer to Drive
Pinion and Ring Gear Replacement (8.6, 9.5/9.5LD, and
11.5 Inch Axles) or Drive Pinion and Ring Gear
Replacement (10.5 Inch Axle).

Pinion and ring gear too
tight

Adjust the pinion and the ring gear backlash. Refer to
Backlash Adjustment (8.6 Inch Axle) or Backlash
Adjustment (10.5, 11.5 Inch Axles) or Backlash
Adjustment (9.5 LD Axle).

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado