Got a 93 XJ. While driving, after replacing the rear drive shaft u joints, I noticed a thumping sound. The sound increased as I accelerated, and decreased as the jeep slowed down. I put it on the lift, put the transfer case in neutral, and hand turned the drive shaft. I could feel a little "play" in the drive shaft and could hear where it was "catching" in the differential. Seems to be about a 1/2" play between the catching. It continues to roll, but there is that catch. Is that normal, or is the bearing in the dif doing out?

 

If it started after doing the u-joint, I'd wonder if you buggered the u-joint. Maybe got one of the needle bearings out of place while pressing it in?

 

I also put on new leaf springs which has raised the back end above the stock height. I you tubed my issue and results came back with the possibility that the angle of the drive shaft to the transfer case is out of spec causing the problem. The solution to fix the angle is to add a shaft similar to the front shaft with a constant velocity joint to compensate for the higher angle. Or I can take the new springs off and replace them with stock springs. to see if that problem persists...or I can keep driving it until it pops.

 

I'd unbolt the u-joint, spin the pinion yoke and see if the catching is still there, and if the u-joint is moving smoothly. Rotate the driveshaft too to make sure it's not the xfer case end binding. Check that the zerk fitting isn't hitting the yoke as it rotates (meaning you should have installed it with the zerk pointing the other way). You can also add degree shims to adjust the pinion angle if needed.

 

You didn't state how much lifted you XJ , but usually the wrong pinion angle creates a vibration rather than a thumping sound. A transfer case drop is a much cheaper cure for that issue then a new drive shaft (with a moderate lift) . Shafts are balanced - that's why they should be replaced in the the same location - mechanics simply mark both the yoke and the shaft to insure this. If you didn't mark the location - simply remove and rotate the shaft relative to the yoke and reinstall. If you guessed right, the thumping should go away