So my xj has had a 3 inch lift kit on it since I bought it and I just put 2 inch add a leafs on it and removed my broken left springs on each side. (The shortest one) Now it's sitting nicely but I get a vibration between 30-45 mph. I've read about people installing a SYE and it correcting there problem. My question is will I need a longer rear drive shaft if I install a SYE?

 

I've noticed that after you change lift height the ujoints can start to go bad on rear drive LINE. At the height I wouldn't bother with Sye. But to answer your question yes you need a different length drive LINE( actually shorter). Usually you can use another front shaft. I would just get some axle degree shims unless you plan to go bigger or have the extra cash to spend. I would not even bother with t case drop. To me those are a waste. Add lift to only lose ground clearance from t case drop is a waste.

 

It's possible. You will need to take measurements to be sure. I've heard of people using another front drive shaft to replace the rear when they do this.

 

on a 97 plus with an automatic the front shaft from another XJ will work fine with an SYE (whether it be a full on SYE or a hack-n-tap). That's honestly your best approach since it will keep working for you if you decide to go with a bigger lift later on.

Like MoparNJeep said, avoid a t-case drop. It's worthless. Axle shims will work provided you get the proper shim degree. Just make sure to install them properly so you don't kill your u-joints and unbalance your rear driveshaft.

The top image is how you need to have it set up if you're not going to run an SYE.

 

I am at 3 in the rear. I actually raised my transfer cas a half inch. Had a vibration at about the same speed. Used degree blocks to angle the pinion slightly upward.

No more vibrations. 2 years now and only one u _ joint replacement in the rear.