help me find the vibe

First the details. 94 4dr xj. 4.0 liter, AW4. NP 231, 8.25 rear axle, RE 3.5" superflex w/ t-case drop. 31x10.5 trxs MT on 15" steel wheels with 3-1/2" back space (i think)

I know i need an SYE so please dont flame me about it.

I had a slight Vibe when i let off the gas at about 50 mph right after i installed the lift about a year ago. Now it is a bad vibe from 15-25 mph either accelerating or slowing down. it is worse when slowing down and the frequency is definatelyspeed related. It seems to be present at all higher speeds except higher in frequency and more constant. I removed front drive shaft with little or no improvement. Removed the rear shaft and had significant improvement but did not completely eliminate the vibration. I am thinking that the u-joints on the rear shaft may be going but i cant feel any slop in them. with the truck on level ground in park i can "rotate" the front shaft about a 1/4" back and forth. it does not look like the front u-joints are wiggling. it looks like the yoke on the front dif rotates with the shaft. one front u-joint and one rear have evidence of grease leaking out. The joints do not apear to be field lubricatable.

Any help is appreciated

I see this all the time,everyone says "I cant feel any movement".Ive seen more joints blow because they were "binding"(dry/frozen) than ones that were greased but just "worn" to death.

you know what....i got almost the same issue...i have a 3" lift and i get a really bad vib at about 15-25 mph but nothing going slower or faster. i too checked the u-joints and got nothin..but didnt even think they may be dried out and or frozen...hmmmm, think i just found out what im doing tomorrow morning before work.

Thanks, I think i'll just replace all of the U-joints, including the front wheel joints. I bought the jeep at 80k miles and now have 130K. I have not done any u-joints and don't know if the PO did so it is probably time.

I would check for play in the joints, do you have a t-case drop? Before I had a sye my jeep reacted differently with vibrations coming and going, until I gave up the shimming the case and pinion angle constantly to fix it.