Originally Posted By: defektes
what vehicle we talking about here?
Check your manual for fluid grade, usually it is 75-90.
To fix a leak you need to loosen the fill plug on the differential, then remove the cover, usually like 10 bolts, keep a pan under the diff to catch the fluid.
Clean the mating surfaces well, they need to be spotless. Clean out as much of the old gear oil as you can out of the differential. Get a tube of RTV sealant ( I use Black RTV by Permatex) apply a 3/8 bead all around the cover, and make sure to go around the bolt holes. Use your finger and smear it around evenly (this will eliminate any air bubbles present in the silicone,) and let it sit for 30 on a sunny day, to an hour on a cold day. Replace the cover, making sure not to damage the silicone, and apply the bolts finger tight in a criss cross pattern. Do not over tighten, once the bolts are finger tight, use a combo wrench and tighten snug, not too tight.
I like to wait another hour or two after placing the differential cover back on and then refill. After a long drive or a couple of days recheck the tightness on the differential bolts.
Perfect advice right there. As a note ATF is not in the differential of most cars and I would guess your diff would be damaged pretty quickly if you used it. Like was mentioned above consult your owners manual and use the exact viscosity product they call for. It can be found at any Pep Boys, Advance, or Autozone.
And the reason you want to loosen the fill bolt first is sometimes it cannot be budged and if that is the case and you get the pumpkin off then you are outta luck because you cannot refill the diff.