xj RE 3.5 Kit installed; my problems

I installed a RE 3.5 Kit on my 89 XJ with a manual 5 speed transmission. I have vibration problems on my rear drive shaft. I replace both ujoints on the rear shaft. The drive shaft vibrates when I accelerate from 20 to 30 mph but no vibrations at hight speeds on the highway. I drove the XJ over 600 miles since installing the RE 3.5 " kit.

I calculated that the angel of the drive shaft changed about 6 degrees because of the installed 3.5" lift. (This is the angle from horizontal at the rear end up to the transmission. The current angle is approximately 18 degrees up from horizontal. The stock angle was about 12 degrees.) I have heard that adding shims to the rear axcle to tilt the axcle up may eleminate the vibrations. I have heard that I should lower the Transfer case crossmember 1" with another kit.

Has anyone installed RE 3.5" Superflex with new rear leaf springs kit? Did you have any problems with vibrations? What did you do to fix your problems.

I also want to get larger tires. What is the largest size tire I can mount on my stock rims? If I want to put 31 x 10.5 tires on the XJ what type of rims should I purchase? What offset should the rims have? What do you measure on the rim and how do you measure it to make sure you are going to end up with a wheel and tire that fits like a stock rim?

This vehicle is my daily driver.

Any help would be appreciated. Thanks.

I've got the same kit on my 91 xj. I had the vibrations and I installed a 1" transfercase drop and that took care of the problems. If you still have vibrations you may need to invest in a Slip Yoke Eliminator.

I've put this kit on a 2001 and a 1997 XJs, both with full new leaf packs. They both drive nice and smooth.
I'd start out with shimming the rear axle and a tcase drop and see how that works. A SYE will not eliminate vibes per say. That keeps the DS from pulling out of the tcase on flexing of the suspension.

Without a SYE you're better off dropping the transfer case first. You want the output of the transfer case parallel with the pinion yoke.

31's will fit fine on stock rims, maybe some very minor rubbing at full tilt. no need for trimming with 3.5 and 31s.

Drop the transfer case and inch and your vibes will disappear. If there's any more, then use a 3* wedge in the back.

This'll solve it.

ciao