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Unread 02-27-2015, 01:12 PM   #1
YJjeeper1
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1989 YJ Wrangler 
 
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Driveshaft Geometry and axle shim questions

Hello fellow jeepers. I have a few questions regarding driveshaft angle. I bought a zone 2 inch lift kit and plan to install this weekend. However it came with 4 degree shims and I am not sure whether to install it or not. My Transfer case output is at 7 degrees and the rear pinion is at 6 degrees. My understanding is that each inch of lift will drop the rear pinion one degree. So I am wondering if the 4 degree shims are too much? My measurements might be off because my rear springs are sagging so much that they have a negative arch, so i know this 2 inch lift will definitely give me over 2 inches.Its essential I get this right because I am trying to avoid a tc drop and the purpose of the 2 inch lift was to avoid a sye. Maybe I am over thinking? The instructions say to use the shim if no other drive line modifications will be performed. Any help is appreciated.

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Unread 02-27-2015, 01:50 PM   #2
timatoe
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I don't think you're going to need the shims, but maybe. With a standard slip drive shaft you want the pinion angle and the t/c output essentially parallel. I may not be understanding what you mean about each inch of lift causing a 1* change in pinion angle, drive shaft angle yes, not pinion angle..... The perches on the axle are keeping the pinion in the same plain regardless of how far up or down the entire axle moves vertically with the spring height (unless I'm just totally missing something).

My guess would be they include the shims assuming you'll go to a SYE in which case you need to alter the pinion angle to point toward the t/c output.
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Unread 02-27-2015, 02:14 PM   #3
YJjeeper1
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From looking at it , that was my understanding as well, I was confused because I had read something different. So anyways, my angles seem to be almost parallel off by .8 degrees, I guess I'll be fine with no shims? What angle on the driveshaft is acceptable?
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Unread 02-27-2015, 02:19 PM   #4
The_Goob
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I would start with no shims if your angles are that close. the driveshaft angle is limited by whats called the operating angle on the ujoint. I dont recall exactly what the limit it on that. You should be fine with that size spring. every jeep is different though. I think 4* is too much for a 2" lift and no SYE
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Unread 02-27-2015, 02:25 PM   #5
bpounds
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I have that lift, plus 1/2" shackles. Nice springs. You will get close to 3" out of that 2" kit. That's the good news.

The bad news is that I tried every combination of shims/no shims and TC drop/no TC drop, and the only way I could avoid vibrations was with the shims and with at least a 3/4" TC drop. I spent a whole day trying to eliminate one or the other. No dice.

I'm all for trying all the combinations to find out how your particular setup works. Just letting you know what I had to do. I will need an SYE to be able to change anything.
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Unread 02-27-2015, 03:07 PM   #6
YJjeeper1
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Thanks for the reassurance bpounds, I did my research and this lift seemed the best bang for my buck for me. I wish there was a one size fits all answer but I guess I'll have to experiment. I'll start with no shims and go from there. I do think the 4 degree shims might be too much but who knows with these YJs.
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