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Discussion Starter · #1 ·
Hey guys I had a question, I had my rear fluid changed back in may, an the speed shop I got my rear oil an posi additive sold me additive for a Ford, on the bottle of additive it said ford big as day ford ,an I ask the guy would it work he said yeah, an now it oct an my posi is going in an out, I have a stock posi an 122,000 mile on the car all highway mile, do you guy think that the ford additive is making my posi act up?
 

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Stock Auburn (Your sig says Eaton with 4:10's).

Friction Modifier, Limited Slip Additive (AKA: Fish Oil) is basically the same stuff whether from Ford or GM, in fact I have heard that the Ford stuff is actually better than the GM stuff.

Did you run synthetic gear oil or regular ole dino, this is the important question.

If you used Dino 75/90 (like you should have). It may just be a bad timing non-related thing and the posi is starting to finally head South on you.

FWIW, I always use two bottles of the FM additive.
 

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Discussion Starter · #3 ·
My sig was a joke, an I never had time to change it, but I used royal purple, the first time this time I got some lucas, because money is tight an royal purple is not cheap.
 

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Royal Purple is synthetic.

Synthetics in the stock Auburn diff is a bad idea.

They dont play well together at all.
 

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Ford posi additive for clutch-type limited slip ("posi") differentials is fine for our cars. For gear-type limited-slip differentials, I don't think you need to add anything.

EDIT - already been discussed here.
 
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