View Full Version : Castor angle, shims, etc.

08-24-2007, 12:14 PM
My 40 is practically dangerous driving on the highway with how it follows the ruts, etc. It's mostly because of my castor being at like -2.5 degrees. I have 2.5 degree shims that will bring it to about 0 (zero). I beleive the spec on castor is +1 (+/- .5)...and I think (hope) this should greatly improve the wandering.


- will adding the 2.5 shims mess with the pinion angle much? (u-joint issues down the road?)
- do I need to worry about shimming the rear?
- Is castor at zero 'close enough' or should try to get to positive?


08-24-2007, 12:31 PM
Lots of good info in this thread:


I went through this routine before Moab this year.

08-24-2007, 01:34 PM
If you're going to the trouble to put in the shims, I'd go higher that 2.5s. 4.0 is probably the next size that is easy to find non custom. You'll likely need to use extended center pins in the springs to be sure the pins make it into the spring clamp plates. You may end up with some driveline vibration but what are you doing with the front shaft spinning on the highway anyhow?

08-24-2007, 03:05 PM
yeah, that's what I was thinking but have the 2.5s already - I'll re-think things.

And you're right - front DS not spinning on the highway...just over thinking things...


08-25-2007, 09:28 PM
I threw 4 degree shims in my front end:


Did a front end shop measure your caster?

08-26-2007, 11:28 AM
front end shop measured them, I have the specs at work. I wanna say -2.1 and -2.5.

I put them on this weekend...we'll see how it is. I just put in the 2.5's we'll see how it is...


03-30-2010, 05:55 AM
how did this work out? i have the same problem!

03-30-2010, 10:33 AM
Sounds like a lot of work to me - I think I better come over and pick up that dangerous vehicle, and study it's habits over the summer. I'll bring it back in October. You could help me out by taking the top off before I get there :D

03-30-2010, 10:40 AM
Nice try, Matt.

The 2.5 degree shims made a big difference, but with the setup I currently have, I might have benefit more with teh 4degree. overall, I'm happy with it.

also be sure to check all the other areas for slop. I had some slop in the center arm assembly, too.