adjusting for caster

Just wanted to get some advice since I'm still new to all this...

Put a 4.5" lift (rough country) on a few months ago. Had vibes and did H&T with front driveshaft in the rear. Still had vibes. Pulled the front driveshaft and it drives great. So I'm assuming its my caster, since the pinion angle is pretty low, on my angle finder I came up with about -2*. I had it aligned after the lift and they took out shims and set it 'to factory specs' which I found out later isnt really what I need for a lifted setup. After looking over gojeeps DIY alignment, I see it needs to be more in the range of +6* (maybe?) so regardless of actual * I need to bring the pinion up to point more at the TC.

My control arms are fixed arms, they are right now at the very rear of the slot holes on the frame. IE as far back as they go. What I want to know is if 1- they are just too long and there isnt a way to adjust anymore to get the pinion up. or 2- if I move the control arms more towards the front and put some shims in if its going to drop the pinion angle or raise the pinion angle? Of 3 - get new adjustables (which I currently dont have money for) Thanks for any help!!!!!

4.0, AW4, 242, 8.25

I'm sitting on a 5.5" lift and currently still have the stock control arms fitted as an interim measure. Had my alignment done yesterday as a base to see how far my caster is out in anticipation of building new control arms. I was amased to note that even at that height I was still within spec wrt caster, albeit on the edge of the lower limit around 5 degrees.

Are your control arms fixed aftermarket control arms or the stock ones? Have a look at Yuccaman's table of control arm lenghts at the bottom of the page that linked. Compare the suggested control arm lenghts with yours and you should be able to figure which way it should be adjusted. Also, bear in mind that pinion angle should also get preference over caster, so unless you cut and turn your axle, caster vs. pinion angles will always be a compromise one way or the other.

With adjustables it really doesn't matter where the factory adjustment slots are as long as they are both the same. If you go longer with the lower arms you are going to push the pinion further away from the correct angle for a CV shaft. You will then need upper adjustables to correct the pinion angle.

You, like me, need to go to some upper adjustables along with lower adjustables. I'm having the same issues with my 96 and 3.5" lift.

I have stock uppers and fixed RC lowers that came with the kit. Regardless of lengths of them the pinion needs to come up. Not really worried about what caster should be as like you said pinion angle is more important to run without vibes. Adjustable uppers does sound like the answer becuase if they were longer then it would push the pinion to point up more. I guess I was just trying to see if there was a fix without buying more parts at the moment!!

Do you have "vibes" or "wobble"? Lowering the caster (to right around 5*) solved my death wobble, but I still had front DS vibes (brand new TW shaft and U joints). It seems my front yoke is slightly sprung and allowed the front U joints to be tighted up slighly off-center. Carefully reseating the U joints into the yoke solved the vibes (I do plan to replace the yoke with a U bolt style on at some point). If you just have "vibes", you might try it.

No never had any wobble. It just gets real rough once I get over 35MPH. I can feel it under my feet just like something is binding up. Took out the front shaft and that cured the problem. I do have another front shaft at home I'm going to try putting in tonight and see if that helps (my front shaft is rusty as anything and its possible my ujoints are worn.

excuse my lack of knowing, but what are the U bolt style your mentioning?

Backroads said:

No never had any wobble. It just gets real rough once I get over 35MPH. I can feel it under my feet just like something is binding up. Took out the front shaft and that cured the problem. I do have another front shaft at home I'm going to try putting in tonight and see if that helps (my front shaft is rusty as anything and its possible my ujoints are worn.

excuse my lack of knowing, but what are the U bolt style your mentioning?

Click to expand...

You can get a replacement yoke that uses U bolts to secure the DS U joints instead of the stock metal straps. They are supposed to be considerably stronger. I would def try a different DS, though you can also try turning yours 180*--sometimes that can reduce harmonics. Mine was noticeable at slower speeds, but got really bad at anything over 60. The caster adjustment had NO effect on this vibe at all (though as I mentioned, did solve my DW issue).

I'm definately gonna try that when I get home (work on sat sucks) and well see what happens. Thanks for the advice and input

When you raise an XJ, using an after market kit, your caster should not change appreciably. The design of the 4-link keeps the caster constant throughout the extension/compression range.
What changes, is the pinion angle; the pinion points down, relative to the transfer case. This results in front u-joint misalignment, and vibration.
Longer control arms are called for, when lifting an XJ, to push the axle forward to center the front wheels in the fender cut-outs, not to "correct" caster. The ONLY way to have correct caster, AND, correct pinion angle is to rotate the "C's" on the axle.
The nice thing with either locking hubs, or an axle disconnect, is, to a great extent, you can ignore pinon angle (as long as the joints don't physically bind up), since you only use the front axle during slow speeds.

xjbubba said:

When you raise an XJ, using an after market kit, your caster should not change appreciably. The design of the 4-link keeps the caster constant throughout the extension/compression range.
What changes, is the pinion angle; the pinion points down, relative to the transfer case. This results in front u-joint misalignment, and vibration.
Longer control arms are called for, when lifting an XJ, to push the axle forward to center the front wheels in the fender cut-outs, not to "correct" caster. The ONLY way to have correct caster, AND, correct pinion angle is to rotate the "C's" on the axle.
The nice thing with either locking hubs, or an axle disconnect, is, to a great extent, you can ignore pinon angle (as long as the joints don't physically bind up), since you only use the front axle during slow speeds.

Click to expand...

I think you'll find that unless both upper and lower control arms are parallel and equal length,(they're not) that both pinion angle and castor will change in droop or compression. If your lift kit comes with lower arms only, they are sized to correct the change in castor angle. Kits that come with both upper and lower arms are sized to correct castor angle as well as locate the wheel fore and aft in the wheel house. Differences in advertised/designed lift height verses actual installed height still require some adjustment to fine tune castor after installation.

xjbubba said:

The nice thing with either locking hubs, or an axle disconnect, is, to a great extent, you can ignore pinon angle (as long as the joints don't physically bind up), since you only use the front axle during slow speeds.

Click to expand...

Those of us with 242s might very well use the front axle at speed--just a thought.

well thats all good info, but doesnt really help the problem. Its not just in 4wd that the problem is occuring. its in 2wd as well. and it is 242 case, so its more of a problem because I use it in all different weather, just because I can. Rain snow, sleet or just because!

what is rotate the C's

I'm actually running my LCA's shorter than stock to get the pinion angle correct. They are at 15 5/8" and I still have 6* caster? Not sure why that is but if I try to make them longer the caster goes overboard and the vibes go to crap.

I'm at 3.5" lift on 31's with light trimming, the wheels are not centered in the wheel wells but they do not rub at flex either.

All XJ's are different, you just have to play around with what you have to get it right.

Backroads said:

well thats all good info, but doesnt really help the problem. Its not just in 4wd that the problem is occuring. its in 2wd as well. and it is 242 case, so its more of a problem because I use it in all different weather, just because I can. Rain snow, sleet or just because!

what is rotate the C's

Click to expand...

He's talking about making the front axle free turning by using something like Warn's kit with manually locking hubs--that way the front DS would not turn all the time like it normally does (even in 2WD). To rotate the C's one would need to cut them off and weld them back on at a different angle. The FSM states that correct pinion angle takes precedence over correct caster. It make take several tries to get something that works. Before messing around with this, I would make darned sure my DS was balanced, my U joints in good shape and the whole assembly carefully centered in the yoke.

ok gotcha on that. So back to the original reason I started the post, I guess what I initially wanted to know....if my other driveshaft proves the same results with vibrations....

My LCA's are all the way to the rear of the slots on the frame rail, if I moved them more foward and was to put a shim in, is moving the entire arm forward going to bring the pinion down or up? From just looking at it, it seems like it would lower the pinion even more, the closer it would get to the front of the slot. I just wanted to know if I can even do that, or If I would be best (obviously) buying adjustable control arms to shorten the LCA up, bringing the pinion up with it..

How bad is your pinion angle? At 5* caster, mine does not look all that bad. You basically want it more or less pointed directly at the xfer case, just like on a rear DS with an SYE. I really don't think I'd worry about it until you try a known-good, properly balanced DS. Before I decided to buy a new Tom Woods shaft, I had my old front DS checked over and balanced by a local shop--it cost all of $35.00. Just my .02 from what I went through getting rid of my post-lift DW and vibes.

I said it in my first post, I measured it with an angle finder and it was -2*. Even just looking at it from the side, you can tell its not pointing at the TC, more looks level with the ground (which proves that with it being even more pointed at the ground with -2*)

Also, the driveshaft never gave me any problems, not a hint of wobble vibration or anything before lifted, thats kind of why I was more worried about the angle being off than the driveshaft being out of balance..

Try a different driveshaft first as the increased angle can make one vibrate if worn even it if didn't before the lift. If the vibes are gone, then problem solved. Often it is the slip yoke. If you can move it up and down at all, it can be enough to give vibes.
Also just where are you measuring the angle at with the angle finder and what is it reading? I know you followed my write up but just want to make sure.

I too have just lifted my rig about 4.5" and I have extreme wobbles, enough to rip my axel out is what it feels like. I was gonna take it into a shop locally on tuesday, they said the charge was gonna be about 95$ to align it and set the caster, thats way to much money. Being such a noob, all I need is the right angle finder and some shims, right? Also I'm thinking I need to push my fixed RE lower controll arms all the way to the rear of the slots?
Sorry to high jack!

PS: I took my front DS out and I am gonna use it in the rear with a RE hack N tap...
97 AX15 D30/8.25

Well I went home and put the other front shaft in that I had, and I still have the same problems, it vibrates again, comes in right around 30 and gets the worst at 35+. The shafts themselves are both sound, no movement in slip joint or when in 4wd no movement from xfer case etc.

Go jeep, I tried using a bevel square last night, (I have a 90* angle with a level on the one side, I was assuming thats what you were talking about) when I use that, putting the one side against either diff cover bolts or the round part next to it, the level is level and my angle finder reads 0*. But I'm not positive I'm doing that right.

I think I am going to have to get adjustable control arms, probably top and bottom, I'm as far back as the arms can go on the bottom in the slots, so there isnt any room for play there to pull it back and bring the pinion up anymore. This was a pretty unexpected problem I was not really anticipating!!!

Selarep, I just did an SYE on my, (re 1801 with spicer) My front shaft was too short for the rear for whatever reason ( AW4 8.25 242tc) I had to go with a grand cherokee one. I think with the manual tranny you MIGHT have to do the same.


edit... Another thing I should note, when looking at my springs from the side (front coil spring) My stock bumpstop on the inside is definately not on the same parallel as the coil itself the coil is...I....and the bumpstop is more like ..../..... of course not that harsh, but looks like if I was to flex it its gonna hit the side of the coil. By that I think that also shows my control arms are not right. I think the fix for everything, from my newb observations is longer upper arms and move the lower arm more to the front, centering the axle more, as well as longer arm up top tilting the axle back to give the right pinion angle? sorry for the book!!! I just want to figure this all out.