Ford Mustang/Capri 1979-1988 Repair Guide

Rear Axle (Differential)



SAE 85W/90/95 hypoid gear oil for conventional and limited slip differentials. For limited slip differentials only, add 4 oz. of the recommended friction modifier (Ford part no. C8AZ-19B546-A).


See Figure 1

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Fig. Fig. 1: Rear axle filler plug

Like the manual transmission, the rear axle fluid should be checked every six months/6,000 miles. A filler plug is provided near the center of the rear cover or on the upper (driveshaft) side of the gear case. Remove the plug and check to ensure that the fluid level is even with the bottom of the filler hole. Add SAE 85W/90/95 hypoid gear lube as required. If the vehicle is equipped with a limited slip rear axle, add the required special fluid. Install the filler plug but do not overtighten.


Normal maintenance does not require changing the rear axle fluid. However, to do so, proceed as follows:

  1. Place a large drain pan under the differential case.
  3. Remove either the rear drain plug (models so equipped), the lower two cover bolts or the cover, and drain the fluid.

To install:
  1. If the rear cover was removed, clean the mounting surfaces of the cover and rear housing. Install a new gasket on early models. On late models, apply a continuous bead of Silicone Rubber Sealant (D6AZ-19562-A/B or the equivalent) around the rear housing face inside the circle of bolt holes. Install the cover and tighten the bolts. Parts must be assembled within a half hour after the sealant is applied. If the fluid was drained by removing the two lower cover bolts, apply sealant to the bolts before reinstallation.
  3. Fill the rear axle through the filler hole with the proper lubricant. Add friction modifier to limited slip models as required.