I have a 2000 Jeep xj 4.0 that I just replaced leaf springs on .. It is stock height and has 200000 miles on it .. When I accelerate from 30 to 40 mph you can feel a distinct vibration from the rear of the vehicle .. I'm not sure if it is u joints or pinion bearings ... Any help is appreciated .. I'm not sure if u joints have ever been done on this xj i bought it about a year ago and only noticed this vibration after installing leaf springs

 

Were your springs sagged real bad?
May be another example of worn u joints unhappy with working at a new angle.

 

My 01 XJ did that for a week or two after I replaced the sagging real springs. Then it stopped. Probably u-joints.

 

Yea old springs were sagged pretty bad .. Put heavy duty ones on so there's a pretty big height difference .. I appreciate the help fellas

 

Sounds like your new parts changed the pinion angle, causing the vibration.
Maybe some tapered shims on the axle housing/spring mounts would help get the angle correct.
Theoretically, the pinion angle should be on the same plane as the transfer case, + or - a couple degrees...

 

Well I was thinking of overhauling the differential and replacing u joints soon anyways .. Do you think the vibration would go away after that ?