Chevrolet 1977 light duty truck Service Manual page 288

BEARINGS AND RACES
F R O N T W HEEL, P IN IO N , DIFFER ENTIA L SIDE A N D REAR W HEEL ROLLER B E A R IN G S
1.
2.
Road Test
3.
4.
5.
1.
2.
Tire Noises 3.
4.
5.
1.
Engine or
2.
Exhaust
3.
Noises
4.
1.
Test for
2.
Wheel Bearing
3.
Noise
4.
1.
Test for
2.
Differential
3.
Bearing Noise
4.
1.
2.
3.
Test for
4.
Pinion Bearing
5.
Noise
6.
7.
DIAGNOSIS
EXCESS NOISE C O M P L A IN T
D IA G N O S T IC PRO CEDURE
Check tires for irregular wear
Check tire pressure
Check lubricant level
Drive to warm-up rear axle
Test at various speeds in drive, float, coast and cornering
Change tire pressure to minimize noises
Drive over different road surfaces
Smooth black-top minimizes tire noise
Cross switch tires, if necessary
Snow tire treads and studs caused added noises
Drive slightly above speed where noise occurs, place transmission in neutral
Let engine speed drop to idle
Stop car
Run engine at various speeds
Drive car at low speed on a smooth road
Turn car to develop left and right motions, traffic permitting
Noise should change due to cornering loads
Jack-up wheels to verify roughness at wheels
Drive car at low speed on a smooth road
Constant low pitch bearing noise may be heard
Noise should not change in reversing turns
Noise pattern should vary with wheel speed
Roughness or whine noise should increase with speed
Noise pitch should be higher than differentials
Test on smooth road to minimize tire noises
Test at various speeds in drive, float, and coast
Rear pinion bearing noise may be louder on acceleration
Front pinion bearing noise may be louder on deceleration
Gear noises tend to peak in a narrow speed range