Driveshaft angle help

My cousin has a 3.5" lifted 99 XJ with the rear C8.25. We did the Dirtbound hack and tap with a modified stock front driveshaft that was rebuilt, slightly shortened, and balanced. We put an angle finder on the driveshaft and got a degree of 17 and on the axle it was 11 giving us a difference of 6. He has no t-case drop and has 4 degree shims. He is getting some vibe around 35-45 still, that are most apparent under load and up hill but can definitely be felt all the time in that speed range. We compared this to my 97 with the same 3.5" lift, same rear axle, no shims, t-case drop, and stock rear driveshaft. The driveshaft is 15 degrees and the axle is 8 degrees giving us a difference of 7 degrees. My XJ has nearly no vibes atleast not from the drivetrain.

What we want to know is if we need to put in the 6 degree shims that he bought or should we look elsewhere to cure the vibes?

Stock rear driveshaft with no SYE, having the 7* or so is correct. With an SYE installed, the pinion angle should be no lower than 2* off the driveshaft. So yes a larger shim is needed. Those types of vibration are typical of the angle being incorrect.

The pinion angle should be no more than 3 degrees difference (0 degrees being ideal) than the driveshaft angle.

You need shims to get the pinion pointed inline with the driveshaft.

Ok then we will definitely put the 6 degree shims in and see where that gets us.

About being at zero though, wouldn't you want it to be just a few degrees off of zero for when the Jeep is loaded down with cargo or a trailer so that the weight doesn't squat the Jeep to where the driveshaft angle is going upwards at the axle end?

Generally anything within 1* is acceptable. Like was said before, generally the target is to have the pinion angle pointed 2* down since the axle will rotate up slightly under acceleration and bring it to 0*.. Weight loading will affect the angle little to none.

I second the above...

Also, I chased vibes for 5 months, till I swapped my front driveshaft to the rear (I have the IRO H&T) (replacing the front used shaft I had back there). Turns out the shaft I bought from IRO with the H&T kit was crap. You might want to swap shafts and just check it out.

Palmetto said:

I second the above...

Also, I chased vibes for 5 months, till I swapped my front driveshaft to the rear (I have the IRO H&T) (replacing the front used shaft I had back there). Turns out the shaft I bought from IRO with the H&T kit was crap. You might want to swap shafts and just check it out.

Click to expand...

Driveshaft is good it was fully rebuilt and balanced by a local driveshaft shop. Also this is a junkyard driveshaft that has been shortened to fit so I can't swap the front for the rear otherwise I would definitely try that too.