Differential Assembly: Testing and Inspection

DETERMINING TYPE OF NOISE
Many noises that are reported as coming from the rear axle actually originate from other sources such as tires, road surfaces, wheel bearings, engine, transmission, muffler, or body. Make a thorough and careful check in order to determine the source of the noise before taking apart the rear axle. Noise which originates in other places cannot be corrected by adjustment or replacement of parts in the rear axle. Rear axle differential gears, like any other mechanical device, are not absolutely quiet and should be accepted as being commercially quiet unless some abnormal noise is present.
In order to make a systematic check for axle noise under standard conditions, perform the following steps:
1. Check the rear axle lubricant in order to assure the correct level, then drive the vehicle far enough to thoroughly warm up the rear axle lubricant.
2. Select a level asphalt road in order to reduce tire noise and body drumming.
3. Note the speed at which the noise occurs. Then stop the vehicle and, with the automatic transmission in NEUTRAL, run the engine slowly up and down through the engine speeds, corresponding to the vehicle speed at which the noise was most pronounced in order to determine if the noise is caused by exhaust, muffler roar or other engine conditions.
4. Tire noise changes with different road services, but rear axle noise does not. Temporarily inflating all tires to 345 kPa (50 psi) for test purposes only, alters noise caused by the tires but does not affect noise caused by the rear axle. Rear axle noise usually stops when coasting at speeds under 48 km/h (30 mph). Tire noise continues but with a lower tone as the vehicle speed is reduced. Rear axle noise usually changes when comparing drive and coast, but tire noise remains about the same. Distinguish between tire noise and rear axle noise by noting if the noise varies with various speeds or sudden acceleration and deceleration. Exhaust and axle noise show variations under these conditions while tire noise remains constant and is more noticeable at speeds of 32 to 48 km/h (20 to 30 mph). Check for tire noise by driving the vehicle over smooth pavements or dirt roads (not gravel) with the tires at normal pressure. If noise is caused by tires, the noise will noticeably change or disappear and appear again with changes in the road surface.
5. Loose or rough front wheel bearings will cause noise which may be confused with rear axle noise. Front wheel bearing noise does not change when comparing drive and coast. Light application of the brake pedal while holding the vehicle speed steady often causes wheel bearing noise to diminish, because this takes some weight off the bearing. Check front wheel bearings for noise and looseness by jacking up and spinning the wheels, or by shaking the wheels in order to determine if the bearings are loose.
6. Rear suspension rubber bushings and spring insulators dampen out rear axle noise when correctly installed. Check that no metal-to-metal contact exists between the spring and the spring opening in the frame or between the upper and the lower control arm bushings and the frame or axle housing brackets. Contact at these points may result in road noise and normal axle noise which would not be objectionable if dampened by bushings.
7. Ensure that there is no metal-to-metal contact between the floor and the frame.

Rear Axle Noises
After the noise has been determined as being in the axle, establish the type of axle noise in order to hell in making any necessary repairs.

Gear Noise
Gear noise or whine is audible from 32 to 89 km/h (20 to 55 mph) under four 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 noticeable, usually 48 to 64 km/h (30 to 40 mph) and 80 to 89 km/h (50 to 55 mph).

Bearing Noise
Faulty bearings produce a rough growl or grating sound, rather than the whine typical of gear noise. Bearing noise frequently has a cyclic hum at the bearing rpm. 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 as required.

NOISE DIAGNOSIS (NOISE WHEN COASTING)

NOISE DIAGNOSIS (INTERMITTENT NOISE)

NOISE DIAGNOSIS (CONSTANT NOISE)

NOISE DIAGNOSIS (NOISE IN DRIVE)

NOISE DIAGNOSIS (NOSE IN TURNS)

REAR AXLE WHEEL BEARING WEAR
Tapered Roller Bearing Diagnosis
Consider the following factors when diagnosing a bearing condition:
1. Note the general condition of all parts during disassembly and inspection.
2. Classify the failure with the aid of the illustrations.
3. Determine the cause.
4. Make all repairs following recommended procedures.

Abrasive Roller Wear
Pattern on the races and the roller is caused by fine abrasives. Clean all of the parts and the housings. Check the seals and the bearings. Replace any leaky, rough, or noisy bearings.

Abrasive Step Wear
Pattern on the roller ends is caused by abrasives. Clean all of the parts and the housings. Check the seals and the bearings. Replace any leaky, rough, or noisy bearings.

Galling
Metal smears on the roller ends are due to overheating, lubricant failure, or lubricant overload. Replace the bearing. Check the seals. Check for proper lubrication.

Etching
Bearing surfaces appear gray or grayish black in color, with related etching away of material, usually at roller spacing. Replace the bearings. Check the seals. Check for proper lubrication.

Bent Cage
Damaged cage is due to improper handling or improper tool usage. Replace the bearing.

Cage Wear
Wear around the outside diameter of the cage and the roller pockets is caused by abrasive material. Wear is caused by poor lubrication. Clean the related parts and the housings. Check the seals.

Indentations
Surface depressions on the race and the rollers are caused by hard particles of foreign matter. Clean all the parts and the housings. Check the seals. Replace the rough or noisy bearings.

Frontage
Corrosion caused by small relative movement of parts with no lubrication. Replace the bearing. Clean the related parts. Check the seals. Check for proper lubrication.

Smears
Smearing of the metal is due to slippage. Slippage can be caused by the following:
- Poor fits
- Lubrication
- Overheating
- Overloads
- Handling damage

Replace the bearings. Clean the related parts. Check for proper fit and lubrication.

Stain Discoloration
Discoloration ranges from light brown to black. This discoloration is caused by incorrect lubrication or moisture. Reuse the bearing if you can remove the stains with light polishing. Reuse the bearing if there is no evidence of overheating. Check the seals and the related parts for damage.

Heat Discoloration
Heat discoloration ranges from faint yellow to dark blue. This discoloration results from overload or incorrect lubricant. Excessive heat causes softening of the races or the rollers. In order to check for loss of temper on the races and the rollers, perform a file test. A file drawn over a tempered part grabs and cuts the metal. A file drawn over a hard part glides readily with no metal cutting. Replace the bearings if you find overheating damage. Check the seals and the other related parts.

Misalignment
A misaligned outer race is due to a foreign object. Clean the related parts. Replace the bearing. Ensure that the races are properly sealed.

Cracked Inner Race
The cracked race is due to an improper fit, a cocking, or poor bearing seats. Replace the bearing. Correct bearing seats.

Fatigue Spalling
Flaked surface metal results from fatigue. Replace the bearing. Clean all the related parts.

Brinelling
Surface indentations in the raceway are caused by the rollers under impact loading or are caused by vibration while the bearing is not rotating. Replace a rough or noisy bearing.

Rear Axle Wheel Bearing Wear Diagnosis
Rear axle wheel bearing wear is described as follows:

Wear (Minor)
Light pattern on races and rollers can be caused by fine abrasives. Clean all of the parts including the housings. Check the seals. Replace the bearings if rough or noisy. Replace the shaft if damaged.

Wear (Major)
Heavy pattern on races and rollers can be caused by fine abrasives. Clean all of the parts including the housing. Check the seals. Replace the bearings if rough or noisy. Replace the shaft if damaged.

Brinelling
Surface indentations in the raceway can be caused by roll either under impact loading or vibration while the bearing is not rotating. Replace the bearing if rough or noisy. Replace the shaft if damaged.

Indentations
Surface depressions on race and rollers can be caused by hard particles of foreign material. Clean all of the parts, including the housing. Check the seals. Replace the bearings if rough or noisy. Replace the shaft if damaged.

Single Edge Pitting
Flaking of surface metal results from fatigue, usually at one edge of race and rollers. Replace the bearing. Clean all related parts. Replace the shaft if damaged.

Double Edge Pitting
Flaking of surface metal results from fatigue, usually at both edges of the race and rollers. Replace the bearing. Clean all related parts. Replace the shaft if damaged.

Misalignment
Outer race misalignment due to a foreign object. Replace the bearing. Ensure races are properly seated. Replace the shaft if the bearing operating surface is damaged.

Frettage
Corrosion set up by a small relative movement of parts with no lubrication. Replace the bearing. Clean all the relative parts. Check the seals. Check for proper fit and lubrication. Replace the shaft if damaged.

Smears
Smearing of metal due to slippage. Slippage can be caused by poor fits, lack of lubrication, overheating, overloads or handling damage. Replace the bearing. Clean all the related parts. Check for proper fit and lubrication.

Knock at Low Speeds
Two situations cause low-speed knock: worn universal joints or a worn and oversize side gear hub counterbore in the case. Inspect and replace the universal joints or the case and side gears as needed.

Backlash Clunk
The following conditions cause excessive clunk on acceleration and deceleration: a worn rear axle pinion shaft, worn case, excessive clearance between the axle and side gear splines, excessive clearance between the side gear hub and the counterbore in the case, worn pinion and side gear teeth, worn thrust washers, and excessive drive pinion and ring gear backlash. Remove the worn parts and replace as required. When possible, select close fitting parts. Adjust the pinion and the ring gear backlash.

REAR AXLE BEARING NOISE
A rough rear wheel bearing produces a noise which continues with the vehicle coasting at low speed and the transmission in neutral. Bearing noise may diminish by gentle braking. With the rear wheels jacked up, spin the rear wheels by hand, listen at the hubs for evidence of a rough (noisy) wheel bearing. Refer to Bear Axle Wheel Bearing Wear.