A humming noise in the differential generally means the ring gear or pinion needs an adjustment. An improperly adjusted ring gear or pinion prevents normal tooth contact between the gears and therefore produces rapid tooth wear. If the trouble is not corrected immediately, the humming noise will gradually take on a growling sound, and the ring and pinion will probably have to be replaced.

It is very easy to mistake tire noise for differential noise. Tire noise will vary according to the type of pavement the vehicle is being operated on, while differential noise will not. To confirm a doubt as to whether the noise is caused by tire or differential, drive the vehicle over various pavement surfaces. If the noise is present in the differential only when the vehicle is rounding a comer, the trouble is likely to be in the differential case.

If the backlash (clearance) between the ring and pinion is too great, a CLUNKING sound is produced by the gears. For example, when an automatic transmission is shifted into drive, the abrupt rotation of the drive shaft can bring the gears together with a loud thump.

The ring and pinion gears can become worn, scored, out of adjustment, or damaged. The problems can result from prolonged service, fatigue, and from lack of lubricant. You need to inspect the differential to determine whether adjustment or part replacement is required.

A differential identification (ID) number is provided to show the exact type of differential for ordering parts and looking up specifications. The number may be on a tag under one of the carrier or inspection cover bolts; it also may be stamped on the housing or carrier. Use the ID number to find the axle type, axle ratio, make of the unit, and other information located in the service manual.

Differential Lubricant Service

Many vehicle manufacturers recommend that the differential fluid be checked and replaced at specific intervals. To check the fluid level in a differential, remove the filler plug, which is located either in the front or rear of the assembly. The lubricant should be even with the fill hole when hot and slightly below the hole when cold.

When the manufacturer recommends that the differential fluid be replaced, remove the drain plug located on the bottom of the differential housing. Some differentials require the removal of the inspection cover to drain the lubricant. With all the fluid drained, replace the drain plug or inspection cover and refill with the proper lubricant.

NOTE

Always install the correct type of differential lubricant. Limited slip differentials often require a special type of lubricant for the friction clutches.

Differential Removal, Disassembly, and Reassembly

Procedures for removal, disassembly, and reassembly vary depending on the type of differential, make, and model. Always refer to the manufacturer's service manual. However, there are several procedures that relate to almost any type of differential.

To remove a separate carrier differential, perform the following:

Remove the drive shaft.

Place a drain pan under the differential. Remove the drain plug and drain the lubricant.

Unbolt the nuts around the outside of the carrier.

Force the differential carrier away from the housing.

CAUTION

A differential can be surprisingly heavy. Grasp it securely during removal. If the differential is dropped, painful injuries can occur.

To remove an integral differential, perform the following:

Remove the drive shaft.

Place a drain pan under the differential. Remove the inspection cover and drain the lubricant.

With the cover off, inspect and MARK the individual components as they are removed.

The procedure for repairing a differential will vary with the particular unit. Always refer to the service manual. When using a service to repair a differential, remember the following:

Check for markings before disassembly. The carrier caps, adjustment nuts, shims, ring and 5-19