Differential Fluid Change

According to our maintenance schedule the Differential Fluid is not scheduled to be changed for 150,000 miles. I changed mine once around 5000 to get any debris that might be floating around and I am changing it again around 30,000. I don't plan on changing it again for awhile.

Note:The 2000 year Mustang manual for the same 8.8 rear end calls for a 80W-90. Not real sure why they changed it to 75W-140. The F150 truck people have had some problems with the 75W-140 and many have gone back to the 80W-90. From what I understand basically is that the lighter oil would be for high speed and the heavier weight oil would be for something under a heavy load. Even jumping all over the Mustang from a dead stop I don't believe that it compares to a truck with a heavy load starting from a stop.
A lot of the retailers that sell after market gears recommend the 80W-90.

You will need

  • 3.75 pints of Synthetic 75W-140, Ford Spec is WSL-M2C192-A
  • Fords Friction Modifier, unless you use a gear oil that already has it.
  • 13mm socket and 3/8 ratchet
  • Screwdriver
  • New Gasket maker
  • Oil drain pan
  • Torque wrench
  • Oil pump
  • Jack stands and jack

I jacked the rear end up, one side at a time and put a jack stand under the axles. Then I took the spare tire jack and jacked up the left side of the car like another 4 inches. This is because with the weight of the body on the springs, the differential cover is harder to remove and replace. No big deal when removing it but you want room to work when you have the gasket maker on the cover and you don't want to smear it before it is in place.

NOTE: Many people will use a floor jack under the differential to lift the entire back of the car up at once, even though the manuals expressly says NOT to do this. People of have done it this way for years with no ill effects. But here is the reason why they tell you not to.

The rear axle is not perfectly straight. To allow the rear end to track correctly, there is about a 1 degree negative camber built into the rear axle. Basically what that means is that instead of axle being parallel with the ground, the differential is a little lower than the center line and the the top of the wheels tilt slightly towards the vehicle.If you lift the vehicle from the differential, you are putting stress on both left and right axle housings where they meet the differential, at the same time. They were not designed to perform in this manner. Although you may not break anything, you do not want to stress this area or slightly tweak it and remove or reduce this 1 degree negative camber.

I removed most of the bolts that hold the cover on and left a couple on, but real loose so as not to just pop the cover off.

Then I gently put a screw driver between the differential house and the cover and opened it up enough for the oil to drain out.

I removed the cover plate and cleaned up the flange of the housing and dried it off.

As long as I was there I checked the torque on the Bearing caps, they are 77 foot pounds and the torque wrench did not budge. Didn't think they would just had to check while I was there.

I scraped the old gasket material off and then cleaned it up further with a wire brush.

Cleaned the outside up.

The manual calls for a bead gasket maker at 1/8" to 3/16" wide. Once you run the bead you need to be ready to install it so make sure you are ready before putting the bead down.

Probably by now the neighbor has stopped by because the garage door has been open for over 15 minutes and he is wondering what in the world are you doing now?

I put the Cover in place and just ran the bolts in finger tight. Don't forget to put the information Tags back on the differential back on. If you don't see them ask Vern, he most likely moved them. Might be a good idea to write the information down now so you will have it instead of having to crawl back under here later. Send Vern home to get a pen and paper, nope you just checked and you don't have any.

I waited about 10 minutes to let the Gasket Material set up a little bit and then torqued the bolts down to 32 foot pounds. If I had thought about it I would have put a washer between the bolt and the information tags because when you torque the bolt down the tag wants to turn with the bolt.

The 1/8" bead was perfect, just the slightest amount of sealer was visible from the outside edge of the case after tightening the bolts down.

My brand of Gasket Maker says that it cures completely in 24 hours. Shop manual says to try and wait an hour before filling with fluid.

Used the 3/8 ratchet and 3" extension to remove the fill plug. It is located in front, on the top and on the drivers side.

If you look closely at the end of the plug you will see it is a magnet, see the swage marks to hold it in place. I cleaned off the metal flakes that will look like just gray dirt. Not a lot there, I have seen them before that looked like they needed a haircut.

The manual calls for filling the fluid to a depth of 1/4" - 9/16" BELOW the fill hole. Or to fill it with 3.5 to 3.75 pints. If you forgot there are 2 pints in a quart so it would be 1.75 quarts to 1.87 quarts. Or if you measure it in ounces it would be 56-60 ounces. I just took one of the bottles and took 4 ounces out so the total should end up to be 60 ounces.

Use a pump available at the local parts store, to pump the oil from the bottle up to the fill hole. If your oil container is like a big squirt tube then you can just hold it above the hole and force it in that way.

Once you have all the fluid in then all that is left is to put the magnetic plug back in, the torque on it is 22 foot pounds.

Hopefully Vern is back with the pen and paper by now.


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