shimming rear axle

right now i have a D35 which is shimmed and a T-case drop. Im getting ready to put in a 8.25 and SYE with CV driveshaft and I was under the impression that I didn't need to shim the axle. my brother told me I need to put in a 6 degree shim though. is this right? I though the yokes needed to be parallel with each other when you have an SYE installed.

A factory stock XJ has a standard u-joint at both ends of the rear driveshaft. The t-case output shaft and the rear pinion shaft need to be parallel (and the u-joints phased properly) to run without vibration.

With a slip yoke eliminator kit, you now have a constant velocity joint at the t-case end, and a standard u-joint at the rear axle. You now want the rear driveshaft and the rear pinion shaft to be parallel. Okay, the pinion needs to be 1-3 degrees down to allow for a little axle wrap.

Why?

A standard u-joint introduces a sine wave in the output shaft. When both shafts are coaxial, aka parallel, they spin the same. As the output shaft gets twisted off axis, it starts to vibrate when the output shaft is not spinning at the same speed as the input shaft.

As far as what you need, the best way is to put in the SYE kit and driveshaft, and use an angle finder to figure out what the angle is on the pinion, and on the driveshaft.

Your brother is right, with SYE you want the driveshaft and the pinion to be in-line (set the pinion a degree or two lower). A 4* or 6* shim is probably just about right.

Woa wait, sorry to hijack but im 90% done installing my 6" rustys lift it came with 6* shims, i used them to point the pinion up at the t-case. Should i turn then around?

And i have an sye installed.

Pinion will need to be tipped up, if you have an SYE.