i have a 79 cherokee that i just replaced the rear 3" springs with 4".  the problem i am now having is that when i drive it vibrates real bad.  it had no prblem before with the 3" springs it had on it. everything was installed correctly so i cant figure it out.  i checked the u joints they all seem to be fine but i am going to replace anyway.  my other question is the rear axle supposed to have an offset toward the passenger side.  i have the t-18 trans dana-20 transfer case, i know the quadratrac has offset rear but does the dana 20.

THANK YOU FIREMAN

Have you looked at your pinion angle for the proper adjustment ? That will induce vibration into the power train, and wear out your u-joints in a hurry. I could be blowing smoke here, I'm not too familiar with Jeeps. Just trying to give you some ideas. Hope this helps.