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Discussion Starter · #1 ·
Hey all,

First drive to work today in my recently-acquired YJ. Ran more-or-less fine except for pretty heavy vibration that feels like the drive-shaft.

I was told by the PO that it sits on a 3.5" lift, but then he also thought it had 31" tires (actual 30"), and that it has AC (wrong). Bit of a brain-donor this guy. He only had the Jeep a couple of months, so I'm assuming at this point the suspension work was done by the previous previous owner.

Anyway, with a 3.5" lift and possibly no other remedial measures, could I get away with some taper shims on the rear axle and dropping the T/case to try and reduce/solve the vibration?

I don't have the budget to immediately start swapping axles, adding SYE, CV drive shafts etc.
 

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Yes, I have a 4" lift which came with the 'wedge' shim and drop bars(about 1- 1 1/4" thick). I had no vibrations. I'd give you mine...I'm in CA. Bay area.
 

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You need to fix the pinion angle with the wedge shims, drop the transfer case a bit, or put in a SYE. SYE is the correct way, wedge shims might be the free way, TC drop is otherwise the cheaper way. I'd say the wedge shims are better than the transfer case drop because dropping the transfer case puts lots of stress on motor and tranny mounts.
 

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Discussion Starter · #4 ·
OK folks, so here's what I found under my Jeep:




Questions:
1. Pinion shaft angle looks wrong, it has a 3.5" lift and it looks like the taper shims could be higher, any ideas?
2. WTH? Are those shocks mounted upside down? The boots are at the bottom...
3. Is that a SYE with CV shaft?
4. Rear UJ has vertical and lateral movement, no rotational movement. Is that the cause of the vibration? Bear in mind I haven't replaced the tires yet so they could be out of balance...

Thanks again
John
 

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Discussion Starter · #5 ·
Nuts, I posted the pics in the gallery and linked to em, but I can't see them
 

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Discussion Starter · #6 ·
 

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Discussion Starter · #7 ·
 

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That pinion angle is way low, shim wedges will help for sure. That is a SYE and looks like a double cardan driveshaft. Picture came out really small on the SYE picture. You should not need a transfer case drop with the SYE but need to rotate that axle to where it's close to the angle of the driveshaft for starters. My rear yoke is slightly lower but yours looks pretty extreme? No vibrations here and I have sye and similar driveshaft
 

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Discussion Starter · #9 ·
That pinion angle is way low, shim wedges will help for sure. That is a SYE and looks like a double cardan driveshaft. Picture came out really small on the SYE picture. You should not need a transfer case drop with the SYE but need to rotate that axle to where it's close to the angle of the driveshaft for starters. My rear yoke is slightly lower but yours looks pretty extreme?
Thanks Steve. The SYE/shaft pic is a link, it'll show up full size if you click on it.

There are already taper shims installed, possibly too small, any idea of sizing? Think I'm going to order 6 or 8 degrees and see what happens...

That shaft angle I think has already eaten a UJ. Busy Saturday I guess...
 

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Here is mine but this is on an 8.8 axle. I gave them my specs, 4" lift, sye and driveshaft and they welded the perches accordingly. I had shims in there but had to remove mine(assuming they thought I did already, I think?) Before removing them it was too high.

ForumRunner_20160224_203539.jpg
 

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You are probably looking at an 8 degree shim. The rear yoke should point at the TC output about 2 to 3 degrees lower. Yes the shocks are upside down, some do this because of contact between the shock tube and axle but unless they are made to run that way (some are) I'd turn them over. Yes you have an SYE and DC shaft, a good thing.
 

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Funny I'm having a similar issue with similar back story! Not to hijack your thread bud but can someone explain what and where shims go?
The shims go between the spring and spring perch on the axle.
 

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Discussion Starter · #15 ·
Thanks again Steve, I measured the shims that are in there, best I can tell is they're at 4° right now so 8° feels right for what I need to achieve but that seems excessive for what I've been told is a 3.5" lift.

Heading to 4wheelparts after work, get the wedges and new UJ
 

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Its kind of hard to make it out but you can see the wedge shims I use to have.

ForumRunner_20160225_123340.jpg
 

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Discussion Starter · #17 ·
Picked up 8° shims and a new UJ this afternoon, gonna fit them this weekend, I have a good feeling about this...
 

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Discussion Starter · #20 ·
4WheelParts, $32.99 for steel. If you need shims don't opt for the aluminium option.
 
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