Driveline Vibes

OK, I've been searcing online about this for a while and made a few posts on here. I just read an article about lift side effects that was posted in another thread, and got my curiosity up. I have a Rusty's 3" Full spring pack lift and a 1" TC drop. In reality the rear is at abot 4" and the front is at about 3.5" (.75" spacers in front too). I have driveline vibes on acceleration from about 30MPH to 40MPH. The guy that installed the lift and TC drop added some 2* shims, but based on that article I beleive the shims may be backwards. Right now they are rotating the differential up in the front to make it more parallel with the drive shaft. Is this correct or should they rotate the diff down to make the output shaft of the diff parallel with the output shaft of the TC?

To make it simpler for my mind this morning, should the point of the shim point to the front of the XJ or the rear?

The shim is installed correctly, the point should go toward the front. You want to rotate the front of the diff up, so it points at the TC.

Correction: You only want the pinion pointed up at the t-case output if you have a double-cardan (CV) joint in the upper end of the rear driveshaft.


If still running a stock-type driveshaft with single u-joints in each end then the plane of the pinion face and the t-case output have to be parallel.

Photos from Tom Woods' Driveshaft www.4xshaft.com

If he has a transfer case drop then it is no longer in a plane with the pinion. Therefore you should rotate the pinion up towards the transfer case.

So in other words, the output shaft of the TC and the input shaft of the diff should be as close to parallel as possible? That is not the case now. Right now, the diff is pointed up closer to parallel with the drive shaft...

Scott Williams said:

So in other words, the output shaft of the TC and the input shaft of the diff should be as close to parallel as possible? That is not the case now. Right now, the diff is pointed up closer to parallel with the drive shaft...

Click to expand...

If you have the stock shaft, then it's wrong. If you had a CV-jointed shaft then you'd be correct with that setup.

The transfer case and the pinion should be in the same plane. Or as close as possible, if you are using a stock driveshaft. If you lower the transfer case 2* then you should pint the pinion up toward the transfer case 2*. This will keep everything in the same plane.

OK, so it is wrong... that's what I thought based on what I read this morning. Let me correct that and see what happens...
Thanks!!!