I've been having this weird thud ding vibration, which I would assume to be my u-joint, my rear leafs are sagging a bit, and I have some 2° shims to go in to adjust my diff. My question is how much damage can I do if I continue to drive it, it's my dd. For reference I have a 3 inch pro comp lift with an added leaf in the back, and 31's. I've been contemplating a bastard pack to make up for the inch I lost since I did the lift.

 

get under it while you have someone put it in drive then reverse with the parking brake on of course and see.

 

I don't follow, you want me to get under a moving car?

 

Haha.. A safer option is to just twist the shafts to see if there is play. If its the rear shaft the u joint is an easy fix, but depending on the year you have, I believe the front shaft has a cardon joint that cannot be rebuilt, but the replacement for my 99 was 85 bucks. And it's a matter of removing a total of 8 (13mm?) bolts to replace it yourself.

 

No, while the jeep is setting in the driveway with the emergency brake ON . Look at the rear diff while someone puts the jeep in drive then reverse. The jeep shouldn't move but you will see the diff pitch.

 

If its a 97 or newer the splines at the trans to driveshaft yoke are dry. Pull drive shaft out and lube the splines and the thud will be gone.
Ron

 

And what will that tell me? Thanks for all of the advice guys! I should have specified, there is a thud when shifting, but the main issue I have is only when I am moving, one thud about every 2-3 feet. Sometimes it goes away too, but it gets quite rough around 35 ish. And its coming from the rear so I know its not death wobble. Also it is an 89.

 

It was a bad u-joint, the front one in the rear drive shaft didn't have enough lube so it burned the bearings away, the gap caused the shaking. Replaced both the front and back ones, no more shaking, and no more clunking when I change gears. Thanks