What brand would be the best, and what grade? Its an 03 XP EB 5.4 4x4
I am planning to change the transmission fluid this weekend and also the transfer case fluid, I know the Tranny should be replaced with Mercon V and the transfer case should be replaced with Mercon. But I was wondering about the Differential since the truck already hit 40K without any of these services.
Also, I have been reading about friction modifiers for the anti-slip differential. how do I know if my truck has the anti slip feature?

Thank you.

Gerardo.

 

Use the recommended grade from the owner's manual and use synthetic from mobil or another good brand. There's a place on the tag at driver's door frame that'll give a number or letter code like H6 which is limited-slip. Also there's a tag underneath on your differential housing whick gives your gear info.

 

Seems to me the differential tag has a L on it for limited slip. Mine says 3L55 and I always thought it meant 3.55 ratio with the L replacing the decimal point to indicate limited slip.
Or you can jack up the rear wheels and turn 1 (in neutral) the other will turn the same direction if it's a limited slip.
Hope this helps

 

I think you have to add a modifier for the LSD, but I've been told to use a Ford product. When I had my rear bearings replaced, the oil alone for that diff was about $75 incl the modifier.