I have a 2006 F150 4x4 with 9.75 rear differential. I have a 6" Fabtech lift and 4.56 gears. The lift did come with a spacer for the rear drive shaft. I had the gears put in by a shop along with the install kit (new bearings, etc..). I noticed a slow leak that looked like it was coming from the front off the rear diff where the drive shaft meets the diff. I replaced the seal you can see from the outside (I think it was called the pinion seal). All I had to do was take the drive shaft off and pull the old seal out with pliers and hit the new one in with a rubber mallet. Anyway, now I can't see any dripping like I could before, but the diff oil is getting slung all over the bottom of the truck when I'm driving. It's on the axle, exhaust, shocks, etc... Where else can it be leaking from besides the seal I just replaced? I need to do something about it soon before all my diff oil gets thrown out and I ruin the bearings

 

If it's slinging , then it's the pinion seal. that's the only moving part.

Maybe you curled the lip on the seal when you put it in. Also I hope you tightened the pinion flange correctly, if it's loose that could be part of the problem.

Why not take it back to the shop that did the install?

 

I got the shop to look at it and they said they what they did wouldn't effect the pinion seal. They told me how to put the new seal in and I replaced it. They didn't mention a pinion flange. What exactly is that?

 

That is the part your drive shaft/ u-joint connects to the pinion shaft.

 

I'm going to have to take it to a shop to get it looked at. I'm back at school now and I don't have the time or space to do anything