I'm at a loss here with gear oils..

[AdamDude04]

Going to do my first rear end change.. ofcourse, want to make sure I do it correctly!

What gear oil should I get?? My haynes doesn't seem to tell me what weight is recomended.. only that I need roughly 5.5 pints (roughly 3 quarts??) dry capacity.

Also something about "Add friction modifier to limited slip diffs. Four ounces for 8.8 inch, and Dana limited slip diffs. Eight for 10.5 inch"

I was just going to buy IIRC 85w90 but I just want to be sure.. and what's the deal with the friction modifier?

 

[Bully Bob]

Wellll...,

If you, in fact, have "POSI" (limited slip diff.) then you need the additive to 80w90. "Posi" won't function properly W/O the additive.

If not, then you don't. 80w90 gear oil is fine.

If memory serves you can still purchase "posi" gear oil already mixed.

Not sure..., but either way will work.

 

[AdamDude04]

How can I tell if I have posi?

I know on our last mountain camp trip I got high centered in some thick mud (ground looked sturdy with moss an all..) and front/rear axle only one tire spun at times.. I assume this is limited slip from my past experinces.

so 80/90 is what's needed?

 

[Bully Bob]

"How can I tell if I have posi?"

Ahhhhh,

Thought you already knew this. Not likely the front has "posi" but for both axles.., (T-case in neutral) jack the front up, lock in the hubs, spin one tire....if the other side spins the "same" direction, it's "posi"....

Do the same for the rear axle.

"so 80/90 is what's needed?"

Yep.., depending on your location....a quality auto parts store mgr. can explain what's best...& will have the "posi" juice..!! /emoticons/[email protected] 2x" width="20" height="20" />

Side-note...some dif's have no drain plugs, or cover plates., sooo.., you have to "****" the old crud out. B)

 

[AdamDude04]

Mine does have the back plate thankfully. I'm scared to open it up and see what's inside!! lol

Thanks!

 

[Justshootme84]

When you go to remove the rear cover plate on your Ford8.8" rear axle, look for the metal ID tag with the gear ratio. A limited slip option will have the "3L55 8 8 ***" on the bottom row of the tag. You can also check the door jamb sticker for axle code "H9". The friction modifier comes in a little 4oz bottle that you add to the gear oil. You will either need to get a new gasket for the rear cover, or use RTV. I use the Permatex copper gasket-making compound. While you have the cover off, take a close look at the spider gears, ring and pinion for any broken teeth, or bits of metal in the oil or bottom of the case. JSM84