SHIMS - Installation Questions

Sep 3, 2003
I have a '79 FJ40 and need some help in clarifying shim installation instructions.

First off, let me say that I have Man-a-fre's steering correction / shackle reversal kit which comes with (2) shims - which appear to be 2 degree. Man-a-fre's directions say "Reinstall the leaf springs with the supplied caster shims, THICK SIDE TO THE REAR.

The Shackle Reversal Kit adds 1 1/4" to 1 1/2" lift. I purchased 2 1/2" front springs and 4" Rear springs in kit form from TPI (Smoky Mountain) in order to get an overall 4" of lift. I also ordered a pair of 6 degree shims as recommended for 4" lift kits.

The confusion comes in that the directions from Spector and others as well as this board say to install these caster shims with the THICK SIDE TOWARD THE FRONT!!

PLEASE HELP! I know up to 5 degrees caster is acceptable or even desirable with 4" of lift, and I know that caster is determined by the angle created by drawing a line through the knuckle bearings as compared with vertical. Also, I understand that the 5 degree caster is viewed from the side and is created by rotating the axle housing so the upper knuckle bearing is now rearward of the lower bearing.

The need for shims is supposedly created because of the axle housing rotation which comes from lowering the front leaf spring attachment by using a longer shackle which creates negative caster. Adding a shim with the THICK SIDE FORWARD then rotates the axle housing rearward and brings the caster back toward positive.

Does anyone have experience with the Man-a-fre kit and 4" lift? Do I use the shims as Man-a-fre instructs with THICK EDGE TO THE REAR, or should I use the 6 degree shims with THICK EDGE FORWARD? Would greatly appreciate any help and / or advise. Thanks very much.

Jim Dahlquist
Georgia Cruisers 4WD Club
Jul 5, 2003
Central, Utah
One of my buddies has the exact same setup and runs no shims at all. I would say put it together and check the angles. If it needs shims install them.
Jun 13, 2003
With shackle reversal big end to the RR. Shackle lift equals fat side front. I would drive it as is and see how it feels then add shims as needed.
Sep 26, 2002
Yakima, WA
My guess is that whoever wrote up those instructions (thick in front) was assuming the shims were going to be used to compensate for longer shackles.

Whichever way you put the shims in, the goal is the same,... equalize, or attempt to equalize the angle of the pinion shaft (and therefore the respective ujoint angles) in relation to the transfer case output.

Be aware of,... if not beware of the words "Always" and "Never".
Jan 30, 2003

Fat side to the rear per the instructions. Fat side front on non SR rigs. Gordon recommends a bronze or steel shim vs the supplied aluminium shims. The degree required in front is going to differ based upon your actual springs so I would put in the 2 degree shims in the front and then see whats up.

Jun 27, 2002
I'm running 6 degree shims fat end forward on my 4" TPI lift with good results, I had them backwards the first time around and it was obvious after a short and scary test drive that the steering was FAWKED.

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