To Shim or not to Shim - Caster correction?

[Chero77]

Problem: Vehicle wanders and steering wheel does not return to center. Not real bad, but its noticable and enough to be annoying at freeway speeds. Has done this as long as I've owned it. Steering linkage, ball joints, etc. are either new are appear to be in good shape. Leaf springs may have been swapped out in the distant past. I say this because the ride height seems to be about an inch or so higher than stock. Alignment is in spec except for front wheel caster. According to Pepboys (about 8 months ago) the front wheel caster is 1.02 degrees right and .94 left. According to an independant shop (2 years ago) its 2 degrees right and left. I tend to lean towards Pepboys as being more accurate. TSM says castor should be 4 degrees.

Have talked to two shops about this (while searching for shims) both say 1 degree is fine, something else is the problem. Various magazine articles suggest otherwise. Opinions? I want to solve the problem and since caster is the only thing obviously out of spec, correcting it seems like the thing to do.

So, I have decided to install degree shims and see what happens. Locally, all I have been able to find are 3 and 4 degree slotted aluminum shims. Are these ok, or should I wait until I can find shims with a hole. A shim with a hole would obviously be better (couldn't pop out). Anyone know of a source? In addition to shims, seems like I will nead longer spring center bolts and maybe longer U-bolts as well? Would be nice if someone made a kit. If anyones ever done this and has some tips please let me know.

If anyone thinks its a waste of time, please let me know and why.

Thanks,
Dave

[mrclean]

Check the local spring shops, especially ones that deal with heavy trucks. They should stock what you need. I'm not a fan of aluminum shims, especially slotted. I would much rather use steel. If you cannot find them locally, email me and I will try to help you. timandde@charter.net

[davez26]

After the lift and everything else, I had a some wandering in my truck, and after freshening the whole front end, I still had it. I swapped tires from someone else and even whipped up a cool dual stailizr setup. Still a little loose. I ended up shimming the front 2 degrees. Much better, not as sweet as my Pontiac, but still much better. As for shims, I agree with mrclean. I ended up at a local spring shop, and they knew what I was after, and had a whole bunch of sizes. I prefer the non-slotted ones as well. It will be important to know the spring width when you go in. As for your spring bolt, ??? depending on what some one else put in there, it could be perfect or to short as is. The only way to know is to pull it. While you are at the spring shop, pick up some fresh u-bolts, because after only a couple years, my didn't want to come off, so I had to cut 'em. and you probably will to.

[porchpiggy]

More than likely a shim you will use will be thin enough at the center that the spring center bolt will still pass into the hole on the spring pad.

[Stolen76]

Don't settle for anything but a steel shim. I'd suggest going 2.5 on the right and 1.5 on the left to start with. Torque down you front ubolts first and you will be very close to 4 degrees right and 3 degrees left.

They are pretty close to even at the moment and you will drive straighter if the right is slightly higher. The DOT standard road grade is 3 degrees for water run off. I've aligned a lot of class 8 tractors with the caster being 2 - 3 degrees higher on the right that road perfectly straight. With smaller vehicles and narrower tracking, I've had good luck with 1 - 1.5 degree differences.

[porchpiggy]

That doesn't make sense to me. If you are increasing castor, you would be turning the wheels/axle bottom back, top forward, and pointing the pinion up, Wouldn't you.???

[porchpiggy]

He wants to gain more positive castor, because the 1 to 2 degrees he has is not enough, should be 4 degrees. So, agreed, to gain pos castor the top of the axle rotates forward, pinion more up. I think?

[Chero77]

According to the Jeep Owners Bible, positive caster is defined as rotating the axle rearward. In other words, if you imagine a line drawn through the center of the ball joints, this line should tilt rearward from vertical. The July issue of 4-Wheel Drive magazine has a sketch and defines postive caster the same way. So 4 degrees positive caster is a 4 degree rearward tilt of the ball joint axis from vertical. Correspondingly positive caster tilts the pinion down. Thus, increasing the severity of that angle. If anyone disagrees with the above please let me know. I don't want to damage my Jeep.

What I am not sure of is to get rearward tilt of the axle do you place the thick end of each shim pointing towards the front or rear of the vehicle??? I got a pair of 2 1/2 degree shims with center holes from 4-Wheel Parts Wholesalers and the guy there said to position the thick ends of the shims towards the rear of the vehicle. I am having a hard time visualizing which way the axle would tilt and am not sure if he is right. Help please?

[JeepFreak]

Ok Dave I deleted all my other posts because they were all jacked up. My whole point was that when you add the shims to gain back some "positive caster" +4 being recommended (+- 1 degree OK) you will be lowering the pinion angle. Don't know how I got so screwed up on my train of thought (I was right the first time before I changed my post). Ok I'm done looking stupid this week smile.gif

If you are spring under the thick part of the shim will be towards the front part of the rig. If you are spring over the thick part will be at the rear of the axle.

[ July 10, 2002, 09:27 PM: Message edited by: JeepFreak ]

[Chero77]

Well, after going out and looking at the axle it seems that to rotate the axle rearward one needs to point the thick part of the shims towards the front of the vehicle.

[JeepFreak]

Yup I was editing my post and you beat me to it.

[Chero77]

JeepFreak, thanks for the confirm. Will be interesting to see if this really affects steering any.