2.5 Inch Lift Shim Degree Question
 

Hey there,

Anybody out there know what degree shim(wedge) I would need on a 2.5 inch lift in the rear to eliminate driveshaft vibration?

I'm running a 99 XJ, 5 Speed Manual. Drive shaft is 29.5 inch long. I went to a friends machinist buddy and he did the math on my lift vs. pinion angle, and he came up with a 5 degree shim. I'm currently useing that shim now with 1/2 inch T-case drop.

Ideally, I would like to retain the normal T-Case height(against the frame, stock), and stay away from an SYE. The vibration starts to harmonize and become really noticeable around 105 kph. My u-joints are new and everything else it tight. I'm just looking for the ideal angle on the shim.

Help????

how did it run before t-case drop and shims?
did you try running it that way
you may not need it

Im running 3" with no t case drop. No shims. And, no vibes. U probly dont need them. And u def dont need an sye.

At first, I had no Shims but had a vibration at about 60 kph, Then I dropped the T-Case 1 inch with homemade spacers, still without shims and had less vibes at 60 but more vibes where noticed at 100 kph.
A fellow jeeper suggested I would need at least 2 degree shims however he also sent me to his machinist friend who made up my current 5 degree shims.
As mentioned earlier, I'm currently running at 1/2 inch T-Case drop, but still am getting vibes. Looking directly at the Driveshaft, the angular difference between the T-case output shaft and the axle pinion is off.
I know they're suppose to be parallel to each other, but how do I get them to that point.

Is there a math formula or something to figure this out? What should I measure and from where? References, etc...

It's comforting to know I shouldn't need an SYE, but how do I get around it and what will I have to sacrafice to regain a smooth ride?

Man, this is frustrating.

huh, this is odd. I'm at 4.5" with no shims, just a 1" TC drop, and no SYE. Are you sure they cardan joints in the driveline are still good? Does it change if you try neutral rolling at that speed?

4.5 inches with no shims? Cool!

I've read somewhere that '97-01 XJ are tempermental, and sometimes that's just how it is, either your lucky with no vibes, or your S.O.L. I guess I'm the latter.

Everything "seems" fine with the cardan's. I've played around with the angle of the T-Case too through shimming the forward half of the cross member and the aft part too. How much play should there be in the slip yoke (vertically speaking)?
At speed, I've tried clutching in, to take the pressure off the driveshaft, and coasted in neutral. The moment I back off the pressure, the vibes go away. Then when I raise the clutch again to maintain cruise speed the vibes come back.

Maybe I should take the 5 degree shims out, cut them down to 2.5 to 3 degrees and see what happens(or just one shim in half, length-wise). Any thoughts? I really think 5 degrees of shim is too much for a 2.5 inch lift application.

Thoughts???