Diagnosis Of The Front Driving Axle; Road Test; Tire Noises; Test For Wheel Bearing Noise - GMC G Service Manual

4C-2 FRONT DRIVING AXLE

DIAGNOSIS OF THE FRONT DRIVING AXLE

ROAD TEST

• Check tires for irregular wear.
• Check tire pressure.
• Check axle lubricant level.
• Verify that the hubs are locked.
• Drive to warm up the front axle.
• Test at various speeds in drive, float, coast and while
cornering.

TIRE NOISES

• Change the tire pressure to minimize noises.
• Drive over different road surfaces.
• Cross-switch the tires, if necessary.
• Smooth pavement minimizes tire noise.
• Snow tire treads and studs cause added noises.
ENGINE OR EXHAUST NOISES
• Drive slightly above the speed where the noise
occurs, and place transmission in neutral.
• Let the engine speed drop to idle.
• Stop the vehicle.
• Run the engine at various speeds.
*TEST FOR WHEEL
BEARING NOISE
• Drive the vehicle at low speed on a smooth road.
• Turn the vehicle to develop left and right motions,
traffic permitting.
• Noise should change due to cornering loads.

AXLE SHAFT REPLACEMENT

M Remove or Disconnect (Figure 1)
• Raise the vehicle.
1. Wheel and tire assembly.
2. Brake caliper (40). Refer to HYDRAULIC FOUNDA­
TION BRAKES (SEC. 5A2).
I ! | Important
• Support the brake caliper (40) so as not to
stretch or damage the brake hose.
3. Hub lock mechanism (20). Refer to "Locking Unit
Removal " in this section.
4. Hub and rotor assembly. Refer to FRONT SUSPEN­
SION AND AXLE (SEC. 3C).

ON-VEHICLE SERVICE

• Jack up wheels to verify roughness at the tires.
For additional diagnostic information, refer to FRONT
SUSPENSION AND AXLE (SEC. 3C).
'TEST FOR DIFFERENTIAL
BEARING NOISE
• Drive the vehicle at low speed on a smooth road.
• Constant low pitch bearing noise may be heard.
• Noise should not change in reversing turns.
• The noise pattern should vary with the wheel speed.
For additional diagnostic information, refer to the 1988
Light Duty Trucks Unit Repair Manual.
'TEST FOR PINION
BEARING NOISE
• Perform the test on a smooth road to minimize tire
noises.
• Perform test at various speeds in drive, float, and
coast.
• Whine noise should increase with speed.
• Noise pitch should be higher than differential noise.
• Rear pinion bearing noise may be louder on accelera­
tion.
• Front pinion bearing noise may be louder on deceler­
ation.
• Gear noise tends to peak in a narrow speed range.
For additional diagnostic information, refer to the 1988
Light Duty Trucks Unit Repair Manual.
• Bearing tests should be done in 2H (after 4H selec­
tion to lock hubs). This removes the transfer case
whine.
5. Inner bearing (31) and seal (32).
6. Splash shield (41) and brake bracket (39).
7. Spindle (38) from the steering knuckle. Refer to
FRONT SUSPENSION AND AXLE (SEC. 3C).
8. Axle shaft (46).
Klrl Clean
• Inner and outer wheel bearing (31 and 26).
• Hub and rotor assembly (28).
• Spindle (38) and spindle bearing (37).
I f f l Inspect
• All parts and replace as necessary. Refer to FRONT
SUSPENSION AND AXLE (SEC. 3C).