I've been doing countless hours of reading up on this but still cannot figure this out.

I have a 2000 XJ Sport. 4.0 Engine, 8.25 rear. About a week ago, I installed a 2" lift with spacers in the front and Leaf springs/shackles in the back. I'm running 235/75/r15 Cooper Discoverer tires.

Since I put the lift in, I developed a vibration between 35 and 45mph and from 55-70mph. I changed rear driveshaft U joints and that helped a little bit. I then dropped the Transfer Case 1" and that completely eliminated the vibrations from 35-45mph. However, I am still experiencing vibration from 55-70mph.

The vibration is felt all throughout the vehicle. You can feel it in the seat and floor the most but there is some slightly in the steering wheel. It is very noticeable around 60mph but when I reach 70 or 75mph, it smooths out. It is also there slightly when I am not on the gas. It is NOT death wobble. I cured that with a new Trackbar.

I took it to a local mechanic who drove it and thinks that the vibration is the front axle U joints. I know that they are bad due to the clicking and popping when I turn and the play in the wheels (I“m changing them this weekend). However, these were bad before the lift. Could these be the cause of the vibration? I think I would feel it at lower speeds too? I thought it may have been an out of balance tire but the shop I took it to wouldn't balance them until after the front U joints are replaced.

So I was wondering, could front axle U joints cause vibration after a lift? Also, do I really need shims or a SYE for just a 2" lift? I didn“t think that I would need a T case drop with just 2" but apparently I did. Any help is greatly appreciated!

I would suspect the stock track bar doesn't like your lift too much. It doesn't matter if it's on tight and doesn't have any loose, the moment you lift the jeep, the track bar becomes too short.

Look into relocating your track bar mounting hole, or even better, getting an adjusting one.

For the TC drop, what you need to be aware of is that they put stress on your engine mounts. I have a 1" drop and everything is fine, but I'm expecting to have to change the mounts sooner or later.

With the little bit of knowledge I have on the subject, I would say the problem could be with your front drive shaft pinon angle.

Since you lifted the front, that alters how the angle of the pinion and drive shaft is. IF you didn't adjust your lower control arms, you may want to try that. ALSO, lowering your transfer case "helps" with the rear for vibrations, but it can cause vibrations for the front then. I say this, because the angle of the transfer case pivot axis is off the engine mounts. So you even out the angles with the rear shaft, but you create worse angles for the front shaft.

Did you try running w/o TC drop after the 2" lift? I had zero problems with my rear at 3" lift with TC up where its supposed to be.

I may be completely wrong, but this is just what I think it could be.

Pre 97 Xjs had a longer rear driveshaft which helps a lot. On my 96 I only had to get a drop once I reached 4.5", under that I did not have a single vibe.

Your suggestion could make sense since OP most likely has the D30 low pinion. Basically you should check your track bar, control arms and front pinion angle.

I've done many of these. A t-case drop is your answer.

If this is true, I have a PRE 97 driveshaft for sale...

He said he already installed one of those, cured the first vibe but another came up.

I might've been a little too general with that claim, I researched this again and it seems to also depend on the transmission type and diff, and whether it's 2wd or 4wd.

Here's quickly what I found :

1997-2001 Chry 8.25 .......... 27 7/8"
1997-2001 D35 ................. 28 7/8"
1987 D44 ......................... 29 5/8"

On my 96 4wd auto it's about 30"

Is there a way to adjust the caster with stock lower control arms? I think my caster may be off as well. But I will replace my front drive shaft U joints and axle U joints too. Thank you guys for all your help. I didn“t think a 2" lift would cause so much trouble

Modifying almost always creates issues. As for the stock arms they can be shimmed to adjust caster some. You will likely need to make your own as most shops will tell you they arent adjustable but they would be wrong.

About how thick should I make the shims? And where do they go in? Thank you guys for all your help

http://www.go.jeep-xj.info/HowtoAlignment.htm

That explains it all well.

Alright I will take a look! Thanks!