i was helping my niece move today and notice my rear diff. cover finally sprung a leak.in the book it says for traction lok axles use a friction modifier.my question is how do i know if my truck needs this or not or do all the f-250's need this.i am doing a complete change not going to recycle the old at 162,000 miles.
thank you adam

 

If it has a clutch pack it needs the friction modifier, when you pull the cover you can look for the clutch pack.

On the door tag it should have an axle code, look up the code and it will tell you what kind of axle it has.

If you aren't sure, the friction modifier won't hurt anything if you add it and it is not a limited slip rear end, but you do need it for a limited slip rear end.

 

Just use the mobil 1, 75-140 diff fluid. Has the modifier in it already, even if you don't have a LSD diff it will work just fine.

Buy Mobil1 Synthetic Gear Lubricant LS 75W-140 (1 qt.) 98FS32 at Advance Auto Parts

 

thanks guys.never had a cover rust through before.i ordered everything i will call and make sure they have the mobil oil in stock on monday thanks again