U joint or pinion bearing?
 

My Cherokee has been making a very loud sound from the rear when accelerating. Its almost howl, but more of a grind and also shakes/vibrates from the rear. When I take my foot off the gas it makes a very feint grinding sound/vibration that comes more from the front, almost right under my feet. I took it to a mechanic nearby and he said it was something in the in the rear and that i should completely replace the rear, which sounds like a bad pinion bearing. But, reading about bad u joints makes me think that might be the problem. How do i find out which it is? It's a 95 xj 2wd sport. Thanks!

Best way is to pull the driveshaft and operate the u-joints by hand. Should move smoothly without any rough or loose spots, or any binding.
Might be worthwhile to pull the rear diff cover and have a look around as well. Metal shavings, that sort of thing. Good excuse to change the fluid too.

well, is there any fluid coming from pinion? and if the u joint is that bad youll probably be able to twist the DS an see the play. sounds like a u joint, cheap and quick fix. it the joint is that bad, go easy on the throttle and fix it asap! if it blows apart while driving its gonna do some damage to something..

Today i jacked it up and was trying to find out what that noise was! I have ruled out pinion bearing since there is no play, but I found out its making noise from the other end of the drive shaft and there is some play. U joint?
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