I have read through a number of threads about caster adjustment. I couldn't find one that matched my situation quite exact. I also didn't want to hijack someone elses thread with my questions.

I have a 2000 XJ, 4.5" lift, adjustable upper and adjustable lower control arms. Adjustable track bar, etc... I DO NOT have lower control arm drop brackets.

I set everything up per installation instructions and I have bump steer like a BOSS. I get it up to about 30 mph and you better hold on. My alignment is good, checked that a number of times. My suspicion is that my caster is off.

I have looked at a number of charts, diagrams, etc... I am an engine guy, but I am pretty new to suspension work. I remember when installing the control arms, that it was a real B***H to get the uppers lined up because of having to fight the springs. I wondered if that maybe indicated that the lengths were off. I now have spring compressors, which should make life a little easier. Anyway, I was curious what the most fool proof way to go about this is. I will most likely be doing it by myself, as my wife is pregnant and is in no condition to be helping out. Let me know and thanks in advance. Hopefully I can get this ironed out before the weather gets nice. Thanks!

 

Can you share your specs and and what setup are you running track bar wise. I just recently installed a rc 4.5 with adjustable upper and lower control arms, my alignment was in spec but I still had death wobble and bump steer. Ultimately I had to switch to the drop track bar with the hyme joint end and a drop pitman arm. Now I'm running with no steering damper and minimal bump steer.

 

interesting. I will take some measurements when I get home in a little bit. I will post them shortly.

 

Here are my measurements.

Track bar. Measured center to center - 32.25"
Upper control arms. Center to center - 15.5"
Lower control arms. Center to center - 14.5"
Differential angle measured by iPhone on diff cover bolt heads - 82.6 deg.

Now, I have 4.5" lift in the front. I have 4.5" full leaf packs and a 1.5" shackle in the rear to compensate for spare tire. Bumper. Etc... It has not sagged at all yet so the back end is higher than the rear right now.

Here is a picture of the pinion angle.

 

Hey man it sounds like you and I have mirror image problems. Here is a site that has been listed on here a couple of different times that may be of help to you.

http://go.jeep-xj.info/HowtoAlignment.htm

I'm like you; engines are easy, suspension is voodoo!

My caster is still not correct. Local off road shop is doing a true alignment on Monday. I have figured out that once you go above stock height, most tire and steering adjustment places are lost like a ball in tall grass. Good luck and I will be following along to see how you come out.

On the link posted, scroll down the page and you will see a table that lists caster angles in relation to the angle of the diff across the bolts. The same place that you measured from.

 

Thanks! I have looked at that site before. I am going to try and pull off my control arms and reset their lengths. I found a site that says they should be approximately 16.5" for the uppers and 15" for the lowers. That is drastically different from what I have. I will try those lengths and see how it goes! I will keep you posted. Good luck!

 

http://www.lunghd.com/Tech_Articles/..._Arm_Chart.htm

Found this thought it might help you or the next dude that does a search with the same problem. I wish my CA's were adjustable, I'd go fix my junk in the driveway right now.LOL

 

That's the exact chart I found too! I am going to adjust my arms to those lengths an are if it helps. Hopefully this weekend I will have results!

 

So what exactly happens at 30mph?

 

It's very unpredictable. It will just wander in random directions. It
Just feels like its on the verge if out of control.

 

That's not bump-steer.

 

I may have used the term incorrectly. But what I described is what it is doing. And even so. My angles and arm lengths are all off somehow.

 

What you're describing is just poor caster. Unfortunately, it's hard to dial in a proper caster and pinion angle once lifted above a certain angle. The only way I know to remedy this is either with offset balljoints or the cut 'n turned knuckles.

 

Check your info one more time. You said 15.5 for uppers and 14.5 for the lowers that's negative caster. Your upper control arms should be 15.0 and the lowers should be 16.5.

 

Well I set my uppers to 15 and my lowers to 16.5. My diff angle is almost perfect according to the recommended angles. Hopefully that fixes my issues! Thanks everyone.