Inspection and Verification

Driveline System

Inspection and Verification
Certain axle and driveline symptoms are also common to the engine, transmission, wheel bearings, tires and other parts of the vehicle. For this reason, be sure that the cause of the concern is in the axle before disassembling, adjusting or repairing the axle.

Certain driveshaft vibration symptoms are common to the front engine accessory drive (FEAD), the engine, transmission or tires. Be sure the cause of the concern is the driveshaft before repairing or installing a new driveshaft.

Axle Noise
A gear-driven unit will produce a certain amount of noise. Some noise is acceptable and audible at certain speeds or under various driving conditions, such as a newly paved blacktop road. Slight noise is not detrimental to the operation of the axle and is considered normal.

NOTE: Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks and wheel bearings as possible causes. Follow the diagnostic procedures.

The noises described as follows usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are the type of noise heard during the road test.

Gear Howl and Whine
Howling or whining of the ring gear and pinion is due to an incorrect gear pattern, gear damage or incorrect bearing preload.

Bearing Whine
Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by worn/damaged pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine which usually comes and goes as speed changes.

As noted, pinion bearings make a high-pitched, whistling noise, usually at all speeds. If however there is only one pinion bearing that is worn/damaged, the noise may vary in different driving phases. New pinion bearings must not be installed unless they are scored or damaged or there is a specific pinion bearing noise. A worn/damaged bearing will normally be obvious at disassembly. Examine the large end of the rollers for wear. If the pinion bearings original blend radius has worn to a sharp edge, a new pinion bearing must be installed.





A wheel bearing noise can be mistaken for a pinion bearing noise. Check the wheel bearing for a spalled cup and spalled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.

Chuckle
Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the differential gear hub and the differential case bore.

Damage to a gear tooth on the coast side can cause a noise identical to a chuckle. A very small tooth nick or ridge on the edge of a tooth can cause the noise.

Clean the gear tooth nick or ridge with a small grinding wheel. If the damaged area is larger than 3.2 mm (1/8 inch), install a new gearset.

To check the ring gear and pinion, remove as much lubricant as possible from the gears with clean solvent. Wipe the gears dry or blow them dry with compressed air. Look for scored or damaged teeth. Also look for cracks or other damage.





If either gear is scored or badly damaged, a new ring gear and pinion must be installed.

If metal has broken loose, the axle housing must be cleaned to remove particles that will cause damage. At this time, any other damaged parts in the axle housing must also be installed new.

Clunk
Clunk is a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE. The noise can also occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components; it is felt or heard in the axle.

Additionally, clunk may be heard upon initial drive-away. This occurs as engine torque shifts vehicle weight, forcing changes in driveline angles which prevent the driveshaft slip-yoke from sliding on the output shaft. To correct this condition, lubricate the slip-yoke splines.

Bearing Rumble
Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a worn/damaged wheel bearing. The lower pitch is because the wheel bearing turns at only about one-third the speed of the driveshaft. Wheel bearing noise also may be high-pitched, similar to gear noise, but will be evident in all four driving modes.

Driveshaft Center Bearing
Rotate the driveshaft by hand. If the bearing shows signs of roughness or is noisy, install a new bearing assembly.

Flex Coupling Inspection
Check for visible signs of tearing, cracking or wear in the reinforcing cord. If the flex couplings show signs of damage, inspect the axle and subframe mounts for cracking or tearing.