What could make my rear end run very hot?. I put Lucas gear oil in it.
I had shop torque the pinion nut. Did they over torque?

 

It's possible that they overtorqued it, But it would have to be by ALOT to make it run hot.

Have you checked to make sure there is actually fluid in the diff? I am assuming that if you added lucas gear oil that you pulled the cover to drain it. did you just add it recently or has it been awhile?

Any fluid leaks from diff or the axle tubes?

How hot is it getting? after little drive a diff will be toasty anyways.

 

wheres it getting hot? The diff or the tubes by the brakes?

 

After come back from shop I drained old oil and refill with Lucas oil. The diff was very hot to touch after 5mil of driving.