I am changing the front and rear diff oil tomorrow in my 04 Screw 4x4
in the manual it states 75W-90 front and rear but I am pretty sure I have seen 75w140 in the rear. can someone please confirm this? is friction modifier required in the front diff

Thanks

 

I would use 75W90 gear oil in both front and rear. You should only have to put the friction modifier in the read diff if you have a limited slip differential in the rear. If you don't have the limited slip then there is no need for the friction modifier.

 

Yes, the manual calls for 75w-140 in the rear. I'm sure 75w-90 would be fine but I'm going to use 140 just because it says.

 

I would would personally go with 75W90 in the diff. 75W140 is a synthetic gear oil and tends to hold in more moisture. To solve that problem switch to 75W90 with the friction additive.

 

I just did both of mine today and Ford recommends 75w-140 in the rear so that's what I put back in....I did notice that my rear fluid was real dirty compared to the front but I hardly ever use 4x4 so maybe that's the reason

 

I hope you added a bottle of Fords friction additive. It's only $8-$9 bucks and highly suggested to add.

 

It's only needed for trucks with LS....which I don't have

 

Sorry, I must have missed that.

 

140 will be fine.

I just used royal purple all the way around and that already comes with the friction additive. $19.00 even from orially,expensive,but well worth it.