Need Shim Position Help

Did I install the shim incorrectly??

I just complete a RE 3.5" lift, on a 2001, auto, NP242, 8.25. Knowing I would eventually need a SYE and CV DS. But in the meantime using a 3* shim on the rear axle.

Vibrations between 15-25 MPH. Have the thin side of the shim facing the front of the car, and thick towards the rear. A friend thinks it is backwards. Did I put it in wrong? I've been reading all the past threads and its mixed opinions? My rear leafs sit on top of the axle...thanks

The XJ is a spring-over axle arrangement. To install a shim in a position that lifts the pinion higher, you need to put the shim in exactly as you did. Fat part points to the rear...

Of course, a shim is only really going to be installed correctly if you measured the angles first and the shim corrects that. On a non-SYE driveshaft, you want the t-case angle to balance out the axle pinion. So...-4* at the t-case means the axle pinion needs to point up 4*. Those numbers are estimates and may not reflect your Jeep.

Jim www.yuccaman.com

I thought you weren't supposed to use shims for the stock driveshaft.

winkosmosis said:

I thought you weren't supposed to use shims for the stock driveshaft.

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That would be the position taken by Mr. T. Woods in this article:

http://www.4xshaft.com/index.html

if you only have one u-joint at each end of the driveshaft then the pinion and output of the xfer case should be parallel. It's when you have the double cardan joint (2 u-joints together) at the xfer case end that you'd like the pinion pointed at or just below the xfer case.

try not to spend a lot of time between 15 and 25 mph?

,

sjkimmel99 said:

try not to spend a lot of time between 15 and 25 mph?

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i get vibes at 48-52 and that's what i do. blow right past either speeding up or down.

to the OP: you could do a TC drop as a bandaid fix...

Thanks for the reply folks :clap:

Looks like I'd better order up a SYE real soon....although the angles look very similar...

the angles may be similar but you also may not have enough of the yoke on the TC output shaft and there is probably an ever so slight wobble caused by not enough positive contact. with an sye the sharpness of the angle matters much less, as long as everything is properly aligned with respect to what it needs to be. hope that made sense. i was under my heep all day...

I experienced the same thing with my 4.5" lift and 2.5 deg shims (I also tried 4 deg and 6 deg shims prior to the 2.5). I did extend my driveshaft 1 5/8" and dropped the transfer case 1" and completely eliminated all vibrations! Extending the driveshaft as I did put it back to the factory position and minimizes the stress on the seals and bushings at full flex. It's an inexpensive way to get by until you can afford the SYE.

Try droping the tcase 1 inch. It can be done many ways and cheaply. The most common method is a 1 inch thick block of aluminum and longer bolts. I have a 4.5 inch lift 4 or 6 deg shims, the rustys 1 inch drop cross member, and girdles on the yoke instead of the straps and have no vibes.

if you dont have a sye you want the fat part facing forward to help get your pinion and tcase output shaft angles. equal. if you have a sye you want the pinion angle to be 2-3* under the driveshaft angle. you can do a drop for a while. but itll stress the tranny and motor mounts more than they already are. ive been trying different shim/lift/tcase drop combos on my xj for months until i finally did a hackntap sye with an auto front shaft. its the way to go honestly. after i lengthened retubed and new u joints along with a yj slip yoke on my stock setup i was in already 180$. then i made another set of t case drop blocks. then i ordered 3 sets of shims and did different lift combos and shim combos and t case drop combos. still had bad vibes above 55. i did alot more up front too! still had vibes.it was hell of rmonths, nothing worked, no matter how perfect it seemed. then i did the entire hackntap sye with driveshaft for under 200$. now i get vibes around 67+ mph only under heavy accel. beacuase i havent reshimmed yet.(15.5* ds angle, 11* pinion angle)
im happy going 65mph with no vibes for now. moral of the story: do a sye. i spent 4 times as much money on random things trying to fix the vibes when the sye ended up fixing it all for the most part. and it easy. and honestly the short shaft kits are not much more involved than a HnT kit and you can get at porc sye for under 200. and a junkyard front autoshaft for 30$. everyone told me to do the sye in the first place, now im telling you, do it. i wish i would have.