Hi guys. I'm new to this forum, but been a fox fan for years. My question is, do I need to run Ford friction modifier with Mobile1 75-140 synthetic? Just drained my diff and wanted to make sure before I refill it.

 

some say you don't some say you do. I used it. It may have enough in it, I would add it imo. too much isn't good too little isn't either.

 

What kind of oil do you run in your diff?

 

I use royal purple with a bottle of friction modifier, and yes rp says you don't need it but still a chance you can chatter and some have, some haven't. me rear end is brand new now but even before that this what I did w/o any issues.