Diff Service

[K2AHollywood]

Sorry in advance because this is a really stupid question but now I am super confused and Im throwing myself out there. So I have searched this site and found many different answers and all my shop data gives me even more choices for potentially wrong information.

My diff is leaking. It needs to be sealed and re-filled. What gear oil weight should I use and synthetic or not? Yes I have gears, no I cant remember which brand so I cant check to see if they recommend syn or conv...does anyone know?

So yeah, I know I need the friction modifyer from Ford...but 75-90? 75-140 (which seems crazy)? 80-90?

 

[Double"O"]

^ i have the same problem...leaky pinion seal fo me...i really need to take of it soon even though i have obly put 400 miles on the car in the last 2 years lol

 

[01yellercobra]

The service manual calls for 75W-140. It shouldn't matter between conventional and synthetic. Usually the synthetic already has the friction modifier in it. So you don't have to add it seperately. The last time I did gears I used Royal Purple gear oil with no issues.

 

[COBRA90GT]

...Usually the synthetic already has the friction modifier in it...

This. :thumbsup: I would go with a synthetic.



OP - Doublecheck and read the product description on the bottle (or company website) to ensure you don't need to add any friction modifier, just to be on the safe side...



:beer:

 

[fastback brian]

typically 75-140 is synthetic and still needs friction modifier..
80-90 is standard oil and needs friction mod.. aftermarket oil companies mixes up all this so it gets confusing. 80-90 is a great oil but needs to be changed more often..75-140 is for long life....

 

[Mystic-SVT]

you will need 75-140, and most likely will need to add friction modifier; go with synthetic

 

[K2AHollywood]

^ i have the same problem...leaky pinion seal fo me...i really need to take of it soon even though i have obly put 400 miles on the car in the last 2 years lol

Ugh mine too. Finally sits in the garage and now it acts like a neglected dog and pisses all over the garage floor.:nonono:

And can the friction mod only be gotten from Ford?

 

[Bite Me]

It shouldn't matter between conventional and synthetic.

Negative, synthetic ONLY in the diff.

 

[K2AHollywood]

Usually the synthetic already has the friction modifier in it. So you don't have to add it seperately.

Can anyone else confirm this? I just picked up Mobile 1, no modifier yet

 

[01yellercobra]

Can anyone else confirm this? I just picked up Mobile 1, no modifier yet

It should say somewhere on the bottle if it has modifier in it already.

 

[99CobraRC]

I read the 75-140 will run cooler. I bought some royal purple that did come with the friction modifier.

 

[K2AHollywood]

Well looks like I dodged a bullet. My leak was coming from the bottom bolt that runs through my Billetflow case cover - so easy fix. Ps, getting that fill plug on and off...what a PITA