Hey guys okay my truck has 150,000 miles on it, it is a 1994 f150 2wd straight six. I am doing the high mileage tune up and was wondering how do you change the rear differential fluid? Is it even a fluid or is it a grease? Thanks again Mitch.

 

It's a thick stinky oil. First you remove the 10 or so bolts from the diff cover. You then have to pry a little to ge the diff cover off. It's usually best to leave one bolt on the top of the cover at first until you get most of it drained. Then you have to replace the cover. You can get a gasket from the part store but more often than not; I find they leak. I recommend you get some gasket maker and apply a bead of it around the diff before you put the cover on. Make sure you go around the bolt holes with the gasket maker...all the way around.
Once the cover is bolted back up; you can re-fill from the back end. Take a 3/8 drive ratchet and remove the fill bolt. Fill her up. I don't remember the capacity.... do you have a repair manual?

Someone might be more detailed; but that's what you get from me.

Check this out! Interesting, they use gasket maker and a gasket.
http://www.obd-codes.com/howto/differentialfluid.php

I use a wire brush via bench grinder to clean up my diff cover from the old material

 

Use 75W90 synthetic or 80W90 dino gear lube. If you have a Trac-lok make sure to use a lube with the correct additives or pick up a 5 oz. tube of friction modifier at the Ford dealer.

The 8.8" rear takes 5.5 pints.

 

I would go with just silicone as a gasket, i don't know why they rec. silicone and a gasket on that website i have seen people do that and it leaks every time.

-Jon