Rear Pinion angle Math

Just finished a RE 3.5" lift and getting awful vibrations on acceleration.

My leafs didn't come with either a spacer or shims so I figured I'd start there. I've been reading the guides but I'm not sure how to get the shim I need. I got an electronic level so I could see the angles but I don't get the math.

My TC has a 4.1 degree drop towards the axle.

My Axle has a 9.0 degree up towards the TC.

Does this makes sense or am I measuring it wrong? I used the same measuring points as this http://www.4xshaft.com/tech_slopesVSangles.html

The angle on the axle is vertical 81 pointing up towards the TC so I subtracted that from 90 to get the 9 degree measurement from the axle end.

How do I get from there to what degree shim I need?

First what year are we talking about?Second assuming we are talking about a stock shaft(no sye kit/no cv shaft),you would need about a 4* shim with the fat part to the rear of the Jeep.

On a non-CV shaft (one u-joint at each end) you should match the angles as closely as possible. If you have 4 degrees at the TC, you should get as close to 4 degrees at the pumpkin as you can.

Yeah, this is a stock shaft on a 2000. So if the TC is 4.1 degrees down off of level and the pinion is 9 degrees up off of level then I should shim the pinion down 5 degrees?

Or should I be doing this angles in relation to the drive shaft and not vs perfectly level? The drive shaft angle is currently 19.7 degrees below level.

Ok, so I think I get it then, measured vs absolute level the TC is -4.1, the pinion is +9.

So the current pinion angle is 4.9. If I add in a 5 degree shim with the fat side to the front of the axle I'll end up with a pinion angle of -0.1.

I've read a few places that the pinion angle should actually not be set to 0 but you should do something more negative to make up for the leafs compressing on acceleration.

So maybe I should get a 6 degree shim which would put me at -1.1 at rest or should it be a 4 degree shim to account for acceleration?

RCP Phx said:

First what year are we talking about?Second assuming we are talking about a stock shaft(no sye kit/no cv shaft),you would need about a 4* shim with the fat part to the FRONT of the Jeep.

Click to expand...

Glad you caught that!