MDonaker

I have a 2001 two door 4.0 with 242 transfer case. I am the original owner. Recently the rear leaf shackles had pretty much rusted through and the rear leafs were sagging pretty badly, so I planned to replace them. I figured I'd use the opportunity to lift about 3.5 inches over stock. This is only the 2nd modification I have made to this Jeep.
I replaced the front springs with RE 3.5" springs. I replaced the rear leafs with new stock replacements, and lifted the rear using relocation shackles at the rear of the leaf spring. All shocks were replaced with new Billstiens. No SYE or drive shaft change.
Ride quality was good as far as the shock and springs were concerned, but I immediately noticed significant drive line vibration at all speeds. I checked the transfer case and rear diff. angle and estimated them (using magnetic angle finder) to be off by about 6 degrees, which I thought made sense given the rear of the leaf was lower than where it had been stock, tilting the rear diff. upward. I put in some 6 degree shims with the large end facing toward the transfer case to drop the front of the rear diff. The vibrations went away at low speed and didn't pick back up until I reached the upper end of third/fourth gear, at which point they returned.
I took the jeep in to a reputable transmission shop and was told I should have placed the large end of the shims to the rear. I went home and gave it a try, and it worked. This makes no sense to me, as it further raised the front of the rear diff. to the point that it is now almost parallel to the rear driveshaft, and no where near matching the angle of the transfer case.
Any ideas why this would have worked and if running this way is going to cause me problems down the road?

Aecon

if you don't have a sye your pinion should be relative to your tcase output. If you're having vibration in this position you probably need new u joints

ffeng31

Have you considered using a transfer case drop kit? This will help to reduce driveline angles as well.

studmuffin

You went up to 3.5 without even a t case drop? You probably trashed your u joints running it like that. Does the jeep sit level? Stock leaf springs with relocation brackets would only five you about a 2 inch lift in the rear.