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Unread 10-21-2010, 08:25 PM   #1
josh86k10
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Leaf Spring Caster Shims

I recently purchased a beautiful '85 CJ7 (258/T176/D300/D30/AMC20 and my very first non-XJ Jeep). The PO installed what appears to be a 1.75" shackle lift with 31's. Unfortunately, funds are a bit tight until I recover from the initial vehicle purchase. While I am not a fan of the shackle lift and will eventually install a proper 2.5" spring lift, fixing the caster angle inexpensively is priority right now.

My current caster angle is 0.7 degrees negative. So, I need a 6 degree shim to be within factory specifications.

Without getting into a debate about the safety of axle shims in general, is a 6 degree shim pushing it? Seems like it will be a pretty thick shim. Should I go with a 4 degree shim and just get in the ball park or go ahead with the 6 degree shim? Obviously, I am referring to a steel shim which is incorporated into the leaf pack via the center pin. I will also be replacing the u-bolts.

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Unread 10-21-2010, 08:59 PM   #2
gojeepin
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There are other ways to change caster but if you're set on shims, use steel shims, get new (longer) centering pins, and bolt the shims into the spring pack.
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Unread 10-21-2010, 09:22 PM   #3
josh86k10
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I realize that repositioning the perches or rotating the knuckles are better options for a permanent solution. However, as I eventually plan to replace this somewhat sketchy shackle lift, I need something easily reversible and inexpensive.

I do not believe that shims are inherently dangerous when incorporated into the leaf pack; however, I do feel that there is probably a limit to how thick one should go due to altered forces on the center pin (it will now be "clamping" an angled surface; I have seen people shim both sides of the spring opposite one another to alleviate this abnormal force). My question relates to whether or not a 6 degree shim up front is approaching or exceeding this theoretical limit.

In short, assuming you think degree shims are safe, do you think 6-degree shims are safe?

Last edited by josh86k10; 10-22-2010 at 04:53 AM..
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Unread 10-21-2010, 09:45 PM   #4
cjdogtoy
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maybe I misunderstand your description, but I thought the spec. was 5 degrees positive witch would imply a 12 degree shim?
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Unread 10-22-2010, 04:49 AM   #5
josh86k10
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factory spec is 5-7 degrees positive. I am currently at 0.7 degrees negative.

-0.7 + 6 = 5.3
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Unread 10-22-2010, 05:54 AM   #6
gojeepin
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Steel shims are considerably thinner than aluminum and I wouldn't recommend aluminum for any reason (front or rear).

I used 10* shims in the rear before I completely rebuilt the CJ, but I sheared the centering pin and the spring pack started coming apart. I relocated the perches when I rebuilt it.
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Vibration? Bump steer? Wandering? Read: Steering, suspension, and driveline basics. An article on how it works and where to look for problems.

83 CJ7, 4.1L 6cyl (4.0L bored .030" over), 35" tires, T-5 transmission, Dana 300 TC, Trussed AMC 20.
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Unread 10-22-2010, 12:23 PM   #7
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I would replace the shackles with near-stock length to improve your caster and deal with whatever flare rubbing that ensues until you get your 2.5" lift.

The other option I would consider (while I hate body lifts in general) is stock shackle length and a 1" body lift. No more.
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Unread 10-22-2010, 12:27 PM   #8
gojeepin
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I agree. I really don't like shims. Use a 1" body lift and the standard shackle.

BTW... to get 1.75" of lift from the shackle they'd have to be 3.5" longer than stock.
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Vibration? Bump steer? Wandering? Read: Steering, suspension, and driveline basics. An article on how it works and where to look for problems.

83 CJ7, 4.1L 6cyl (4.0L bored .030" over), 35" tires, T-5 transmission, Dana 300 TC, Trussed AMC 20.
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Unread 10-22-2010, 03:41 PM   #9
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Quote:
Originally Posted by gojeepin View Post
BTW... to get 1.75" of lift from the shackle they'd have to be 3.5" longer than stock.
Correct. I misspoke.
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