Ok, I asked this a few days ago but never really got an exact answer. My question is.

New fluid was added, They put in 80w/90 normal gear lube with posi additive.

The rear end states Synthetic only 75w/140.

I have shopped around for it. Dealer wants 27.50 per quart

Parts store has Redline symthetic 85w/140 for 8.79 per quart.

Rear takes 3 quarts. So is the normal 80w/90 ok? should i change to the redline 85w/140 or pay dealer 90 bucks for the ford stuff?

I do not want to cause damage to posi unit so am looking for advice.

Thanks

 

Great question as I am in the same dilemma. I called SVT this morning and they said go with 80w90 as printed in the SVT owners supplement. They told me that the 75w140 is to heavy and you will get better performance out of the 80w90. SVT could not explain to me why there is a 75w140 tag on the diff.

Hope this helps

 

This question has been asked before, I am not 100% sure but I believe the SVT suppliment is wrong. I feel it is safer to go by what is stamped on the tag on the differential.

 

I would just bite the bullet on this one and go threw the dealership for the synthetic. Its always better to be safe then sorry. Better to spend the $82.50 for 3 quarts then GOD knows how much for a rearend.