Project: Diesel power

[Dave]

Changing the differential fluids.

This is a pretty important service no matter what you drive, in my opinion. I'd much rather spend $30 on a quality gear oil than have to buy a new diff, too. I used Mobil 1 75W140 for the rear and Mobil 1 75W90 for the front (those are the recommended weights).

The rear diff is held on by (12) 13mm bolts. Bust them all loose and remove all, leaving 2 at the top. Now, using a putty knife, very thin prybar, or small flathead screwdriver, we need to open the diff. Let the goop run out:


Once it is done, you can pull off the last 2 bolts and remove the cover. The gears look like this:


The ford guy was right, my rear really did need to be changed (there's lots of little flakes)


In the meantime, while the rear is drip drying, I went around to the front and cracked that one open. It is held on by (9) 14mm bolts and a 5/16" allen bolt. This fluid reminds me more of snot and is considerably thicker.


Now that you have both covers off. You might as well treat them and maintain them for longer life. First clean the inside out really good. I wiped them with a rag to get a lot of junk, then used brake clean to blast it and help it out. Also, scrape off all of the old gasket material. A little light sanding (very fine grit) is good here to make sure all the crud is off. I also used a bit of laquer thinner along the sealing surface of the pumpkin and the cover, just to give it a little extra clean. It should look something look this when you're done with them:


Unfortunately, the outside looks like hell still. I wirebrushed the shit out of them to scrape off all the crap and get to spots where rust was starting to form. The rear shell in particular was looking rough. Normally, I probably would have gone ahead and replaced it. However, since it had so many flakes in the fluid and had obviously been neglected, I decided I would be changing my rear fluid again at a shorter than recommended interval and would replace the cover then. This is what my covers looked like after cleaning them up.


Now, you can stop there and reinstall, but I'm a big fan of making it better than I started with. So I made sure they were good and clean, then sprayed both with multiple layers of rustoleum. It's preventative, and it makes it look good at the same time. Bada-bing!


Once the paint is dry, make sure your sealing surface is nice and clean on the cover and apply a bead of black RTV along the edge, as well as around the bolt holes for complete coverage. I spread it with my finger. You want to allow this to sit for 20 minutes and partially cure.

During this time, I cleaned up the surface on the differential to ensure a good seal. I should also note that earlier, I squirted some of the fresh fluid into the diffs in an attempt to drain out some old fluid that might be caught in crevices, nooks, and crannies :-). Can't hurt, right?

Your RTV should be setting up by now, so lets slap it on. Once it is in place, thread your bolts in until you can't turn by hand any more. Torque in a star pattern to ~35 ft/lbs. Allow to cure for 1 hour before you put the fluid in. Go have a beer, you're almost done.


The final step is to literally fill the pumpkin till it pours from the fill plug. Apply a 3/4 turn bead of thread sealant on the plug, thread it in and torque to 20 ft/lbs.

Keep an eye on it for a couple days to make sure it isn't leaking. Voila!