Castor Shims

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May 19, 2010
Lancaster, CA
Hi guys, I've been having bad steering problems (wandering, darting, etc) with my 75 FJ40 since I bought it two years ago. This truck was mainly used to go around town one weekend a month or so at best so I never made it a priority. Now I would like to use it more during this summer, so I decided to try to finally try to fix it.

My truck has front shackles that are 5" pin to pin, and I'm not sure what lift springs the PO had put on but they are definately not stock.

I measured my castor angle last night and if I measured it correctly (magnetic angle finder on face of pinion flange with front driveshaft removed), it read -4 degrees.

So with that information, should I look to getting shorter front shackles, or I am ok with just getting shims? Also should I get 6* or 8* shims? My truck does have power steering.

Thanks for the help
I put 2 degree shims in mine, I may go to 4 and its about 3 inch or so sua lift. It would basiclly go direction you pointed it in without any tendencey to return to staight and level flight. Nice at 5 mph but scary at speed.

Castor angle is a derived angle of a line thru the knuckle bearingss (kingpins, ball joints or whatever the vehicle has). Spec, I believe, is 0 degrees.

Check your toe in and for any stiffness in the steering shaft/linkage too.
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Stock caster is 1 degree positive caster. Between 1 and 2 is generrally acceptable. Larger tires can get away with 2 - 3 degrees. Zero and negative caster is a sure fire way to set up the "death wobble". Any worn/loose components (including the p/s gearbox) will add to or magnify problems caused by negative caster. If you are reading the caster right, 6 degree shims should bring you back to stock. Letting local tire shop check your caster would give you a much more accurate idea of what you have.
Whenever you get your shims, get steel shims, not aluminum. Great advice from the forum that I picked up last year. They will last. OrangeFJ45 has them in steel, as well as, a few other vendors. I used 4 degree shims and I have a SUA 4" lift with 33" tires. Took care of a LOT of the darting. I also replaced tie rod ends, rebuilt center arm, etc, etc.
Negative caster is real bad! We run ours on the high side (3+ degrees) when we can (on non-LCs). Not as much freedom with leaves unless you cut your knuckles.
In my experience, more caster the bigger the tires are.

I'd recommend 4° on 33's, and 5-6° on 35+

I've ran up to 10° caster with shackle reversal to help with steering issues, so if anything, be more aggressive with the angle. (all with power steering)
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Thanks guys, contacted OrangeFJ45 about some shims, just trying to decide if I should get 6* or 8*? Thanks
If you have manual steering, you're going to want low positive caster or it will be even more difficult to steer. If you have PS, 2-3* is good.
If my measurement was right, 6* should get me to +2* and 8* to +4*, will going with the 8* shims, bringing it to +4* be too much? I do have power steering. Thanks

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