Changing Rear differential fluid

DaMoose81 · #1 09-16-2008, 12:17 PM

So ive searched my butt off and have come up with a conclusion after reading 100 plus posts. On my 06 4.6 4x4 3.55 LS this is what ill need.

75-140 Royal Purple fluid (no extra additive needed due to RP)
A seal
tools.

The questions are:

Do i need RTV or sealent for the gasket? If so do i just put a light coat on both sides and what kind of RTV do you recommend?

Do i fill it all the way up till it comes out the top or put exactly what the manual says to put in?

milkthegoat · #2 09-16-2008, 12:41 PM

Not sure about the RTV on the gasket, maybe just to hold it on while you put the cover back on. idk. But you will know its full when fluid comes out the fill hole. It should be right up to that mark.

minimonster17 · #3 09-16-2008, 01:37 PM

get some blue permatex, this is what ford uses. put it only on the axle pumpkin, not the cover. make sure to clean the axle and cover as thoroughly as possible to allow the permatex to seal properly.

also, you'll want a transfer pump to put the fluid back in w/, makes things so much easier.

mobil1 will work just as fine too, and is probably more available. it has the LS fluid as well...

glc · #4 09-18-2008, 01:14 PM

The factory uses RTV only, no gasket material.

DaMoose81 · #5 09-18-2008, 02:17 PM

Is it going to hurt anything if i put a gasket in it? I got one from ford, and why only put RTV on one side of the gasket?

DaMoose81 · #6 09-19-2008, 11:11 AM

anybody?

DaMoose81 · #7 09-19-2008, 08:25 PM

so gasket with one side rtv'd?

fordmerc · #8 09-19-2008, 10:58 PM

I used to rebuild diffs for a for dealer and we never used a gasket. All we used was BLACK silicone, we put it on the COVER. let it sit for 10 min and fill er up with fluid. Never had a problem.

BASS ASSASIN · #9 09-19-2008, 11:06 PM

i've done 3 -f150's and i used red high temp silicone, and used 75w140 synthetic, and if you have a limited slip rear you need a bottle of the additive ford sells to get the clutch packs to engage correctly.

glc · #10 09-20-2008, 12:22 AM

Additive not needed if you use Royal Purple.

You can use a gasket if you want to.

BlueOvalFitter · #11 09-20-2008, 10:51 AM

If it is the 8.8 rear end I would use a gasket.Fel Pro makes one;
Part # RDS-55341
Put a very thin layer of RTV on both sides.Also,even tho the differential fluid says it has the additive in it I would still buy a bottle of friction modifier from Ford and add it!

DaMoose81 · #12 09-20-2008, 03:17 PM

cool, thanks guys, i already have the gasket, and it is a 8.8 i believe.

AZInfidel · #13 09-21-2008, 03:44 AM

Quote:

Originally Posted by fordmerc

I used to rebuild diffs for a for dealer and we never used a gasket. All we used was BLACK silicone, we put it on the COVER. let it sit for 10 min and fill er up with fluid. Never had a problem.

Same here. I'm a Ford tech and have done countless rear-diffs. Make sure you clean the surfaces of the axle housing and the cover (grinder with a pad and brake clean work perfect) and put a bead of the black or gray silicone on the cover. There's no need for a gasket but, if it makes you feel better. I've always used Ford's 75-140 and fricition modifier, haven't messed with RP, but just fill it up till it's level with the fill hole.