I have a 2000 xj with a 2"bb auto trans, at 60mph+ it gets very loud inside. I removed the front driveshaft and it is gone. Is it the driveshaft or front axle pinion bearings or what? Thanks for the Help!

 

Wait...you removed the axle and drove it? I am assuming you mean the driveshaft.
It could be a bad u-joint in the driveshaft, axle shafts, pinion bearings, pinion angle, lots of things can cause a vibration.

 

How can I track down the cause?

 

If the driveshaft is stillout grab the pinion shaft and see if it has any side to side movement in it.. if it does its the pinion bearing.

How are the u joints ? when you work them are they smooth or catch and feel rough?

If those 2 things are good jack up each side one at a time, remove wheel and turn the unit bearing by hand.... any play? does it feel smooth or rough when turning?

Next step if those things ck good is to leave driveshaft out, pull the axle shafts, (ck their u joints) reassemble without the axle shafts in and test drive..

If the vibe is gone then its bad carrier or pinion bearings.

 

also check the slip joint on the front driveshaft. It should have little to no movement. Mine had 1/4" to 1/2" and caused vibration.

 

pjsjeep is right. it was the slip joint on the driveshaft. $30 at the junkyard. THANKS