Truck has 170k, decided I might as well change the rear diff fluid and paint the cover while I'm at it. I looked at the tag on the rear end.

It says: S-115 L , Then on the next line: 3 10 2 1E03

I take this to mean it has the 3.73 LSD Rear, which is expected since it's a 2001 7700. Anyway, I know I need to add friction modifier (unless it already has it in the fluid). But I have no idea which fluid to get for it. Is it 75/140? 75/90? 80W/90? Also, how much should I get?

I also read that gaskets pretty much don't exist for this rear end, so I'll use black silicone RTV no problem.


Thanks for your help.

 

75W140 full synthetic, 7 pints. Get friction modifier from the Ford dealer.