Axle Noise

Axle Noise

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

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

Gear Howl and Whine
Bearing 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 is a high-pitched sound similar to a whistle. It is usually caused by worn/damaged pinion bearings. 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. Pinion bearings must not be installed new 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 original blend radius of the pinion bearing 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. On 2-wheel drive vehicles, check the wheel bearing for a spelled cup and spelled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.





If the wheel bearing is damaged, the roller surface on the axle shaft may also be damaged. Install a new axle shaft if any damage is detected.
On 4-wheel drive vehicles, check the wheel bearing for rotating smoothness and end play. Install new as required.

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 of the driveshaft speed. Wheel bearing noise also may be high-pitched, similar to gear noise, but will be evident in all four driving modes.

Axle Shaft Bearing Noise
Axle shaft bearing noise is similar to gear noise and differential pinion bearing whine. Axle shaft bearing noise will usually distinguish itself from gear noise by occurring in all driving modes (drive, coast and float), and will persist with the transmission in NEUTRAL while the vehicle is moving at the speed in which the concern is occurring. If the vehicle makes this noise, remove the suspect axle shaft, install a new bearing and a new axle seal. Re-evaluate the vehicle for noise before removing any internal components.

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 damaged badly, 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.





Knock
Knock, which can occur on all driving phases, has several causes including damaged teeth or gearset.
In most cases, one of the following conditions will Occur:





1. A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.

2. NOTE: Measure the end play with a Dial Indicator with Bracketry, not by feel.

Knock is also caused by excessive end play in the axle shafts. Up to 0.762 mm (0.030 inch) is allowed in semi-float axles. The frequency of the knock will be less because the axle shaft speed is slower than the driveshaft.

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, preventing the driveshaft slip-yoke from sliding on the output shaft. To correct this condition, lubricate the slip-yoke splines.