Mustang Differential Maintenance

Mustang 8.8 inch Differential Fluid change and Cover Upgrade.
This is important maintenance that is often forgotten or neglected and if not done can lead to catastrophic rearend damage. Not changing differential fluids can lead to bearing failure and differential gear destruction resulting in a total loss of function and drivability. You should inspect differential fluid levels yearly and if you have a leak repair immediately. 

Tools Needed:
Ratchet 3/8 Drive
3/8 drive 1/2 socket
gasket scraper
New Differential Cover Gasket Non-stick or Standard (your preference)
New Differential Oil and Ford Recommended Additive
Paper towel or disposable shop towels

If installing the GT500 Aluminum Cooler cover
10      5/16-18 x 1 bolts will be needed
1        7/16 - 20 bolt to cap off vent hole on GT500 cover

Note: My 79 Mustang has an 8.8 inch rearend from a 1992 Mustang GT and this is why the GT500 Cover works. 

As part of the cleaning process make sure to remove all gasket material and RTV if previously used from the mating surfaces of cover if reusing and differential housing.

After a majority is drained you may need to reach in with your hand and some towels to clean bottom of differential case. 

As you can see the 8.8 I have already has a vent for the axle here. I bring this up because the new GT500 Differential Cover and cooler is designed to have a vent added into it.

This is the Vent hole I will cap off. using a bolt and RTV. Bolt size is 7/16 - 20, which is fine threaded.

Now these are the original bolts in which are too short for the Aluminum GT500 Differential Cover.

As you can see from the Pictures below you will need to buy longer bolts. 

The size of the bolt you will need is 5/16-18 x 1 this will give you what you need in length. You will need 10 of them. I bought mine at Farm & Fleet and now you don't need anything fancy Grade 5 will do for something that hardly has a torque spec.  

Now here I put the top center bolt through the top center hole and used that to hold the differential gasket in place. Carefully started the threads to hold everything. The fins on this cover are designed to expel heat and assist in keeping differential fluid temps down under hard use. 

Now here you after all bolts are started you will tighten things down in a crisscross pattern then torque down in a crisscross pattern. Here you can see me use a paint pen to mark bolts as I torque them. For the Aluminum cover the torque spec is 24 ft lbs.

After everything is torqued you will move on to refilling the differential with Ford Recommended differential fluid and additive. If you have the GT500 Cover installed, you now have two fill options. A plug in the top face of the cover and the front of the differential as pictured below. If you use the hole on the cover be sure to open the front fill hole so that you can monitor level and prevent over filling the differential. I just filled differential from normal location.

Once filled reinstall the differential fill plug and monitor for leaks. If done as instructed you shouldn't have any.

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