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unlimited4x4

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Discussion starter · #1 ·
I need help with my controls arm. I just replaced the lower front control arms with a new set of the RC adjustable control arms. The front end has been doing some unusual things after the install. So I inspected the jeep today and found some irregularities that could only be due to the CA length. According to the instructions, the arms should be 15.5 inches for the 4" lift. The RC rep said 15.25. I set them at 15.5 and then had my local shop install them. Today I noticed the location of the bumpstop on the drivers side vs the passenger side. See the photos below.

The first photo is the passenger side, so the rear of the vehicle is to the left and the front to the right. The bumpstop is noticeably not centered.

The second photo is the driver side, so the rear of the vehicle is to the right and the front is to the left. Here the bumpstop is relatively centered.

After doing some measuring, the driver side CA is slightly longer than the passenger side CA.

I have read so much on the internet on CA lengths that I am at this point very confused. I have learned one thing, despite the endless hours of reading, I don't know as much about properly setting up the jeep as I thought. Im gonna say that there is no set CA length for any one jeep. I have seen numbers from 15.5 to 16.3. Ultimately it comes down to proper axle geometry.

So i need this groups help and advice/direction to get the CA's set. After doing further reading, my plan is to put the jeep up on jack stands, remove the tires and adjust the lower control arm lengths until the center of the axle hub is centered in the wheel well. This should center the tire, which from my reading is what I should have been looking at from the beginning and not the CA length. I am assuming that the bump stops should also be fairly close to center(yes/no?). When centered the length of both control arms should be the same? Is this the better way to set the lengths?

After this is done, I can then use the adjustable upper arms to set the proper caster.

In the end, if this is correct, Ive learned there is no set CA length "recipe" for a given jeep type with a given lift height. It all comes down to geometry.
 

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#2 ·
unlimited4x4 said:
I have read so much on the internet on CA lengths that I am at this point very confused. I have learned one thing, despite the endless hours of reading, I don't know as much about properly setting up the jeep as I thought. Im gonna say that there is no set CA length for any one jeep. I have seen numbers from 15.5 to 16.3. Ultimately it comes down to proper axle geometry.
Click to expand...
anyone that tells you to set the lower control arms in the front to less than stock doesn't know anything about basic high school geometry.

In front, stock lowers are 15.75", uppers are 15". Lift a Jeep 4" with stock length control arms and you'll get pretty bad caster. Lift a Jeep 4", then shorten the lowers and the Jeep will drive very bad, with terrible axle position.
 
#3 ·
I wont be much help cause my springs look similar to yours, however I am very interested in what people have to say. I have a 4 in lift with fixed after market LC's. Not sure what brand of lift as it was on the jeep when I bought it. My bump stop rubs the spring on the passenger side when the sway bar is disconnected. I plan on getting adjustable LCA's as well, for now though, she is just gonna have to rub a little.
 
#4 ·
I recently replaced all my control arms with adjustables that came with a 4" savvy/currie lift, and would like to see what others have to suggest to you to see how good or bad I did....

I did lots of reading, and talked with several jeepers before starting, but still had lots of questions. I think I've got it all sorted out now, but want to see what others say to double check.

For the front. I started by replacing the lowers. The instructions that came with the lift had starting *suggestions* for length. I set the bottoms to those suggestions, then replaced the uppers with the suggested lengths (don't recall what they are, but can look them up if needed). I left one of the uppers disconnected, and measured to make sure my axle was square to the frame by adjusting the lowers.

Once square, I adjusted the disconnected upper to fit the new adjustments. At this point, I checked for binding by using a jack to run the axle through its flexes. Both sides full stuff, then one side full stuff with the other at droop, then vice versa. While doing this, I also checked where the bumps hit. This was done without springs installed and with the steering and sway bar disconnected. The shocks and trackbar where in place for this (they were in place, but not really "installed", they were put in just to help check for binding).

Once I was happy with that I installed the springs, shocks, and steering links. Put the wheels back on it and set it on the ground. I then installed and adjusted the track bar. I then started checking for caster and pinion angles. I installed a 4" lift, so I knew my caster was going to be different then stock. Per recommendations, I set the pinion angle as close to 0 difference from the drive shaft as I could (I think I actually ended up at about 1 degree off in favor of caster... but what I read +/- 1 degree was okay. I was only a degree or two off, so it wasn't too bad. My control arms are double adjustable, so I didn't have to disconnect them to adjust them. I made a mark on each arm with a sharpy, and made the same amount of adjustment to each side.

Once that was all done, I did a quick driveway alignment, and was good to go!

The rear was done the same way. The only difference is the pinion angle adjustment. I haven't installed an SYE yet, so instead of setting the pinion to 0 (+/-1) of the drive shaft, I set it to the same angle as the output shaft of the t-case.

Not sure if this is right or wrong, but its served me well so far! The jeep drives great, and aside for a little drive line vibrations, I have no complaints. The vibrations are getting fixed this weekend with a MML and maybe some washer under the skid. SYE will be installed in the spring while doing some transmission work, followed by a tummy tuck.
 
#5 ·
I am not an expert, I guarantee that. But I went through this, twice now. The stock lowers front and rear are 15.75 and my Currie arms came set to that length and that setting was said to be correct in the instruction sheet, preset, supposedly. I do not believe there is significant variation in Jeeps. They are factory assembled. I would be surprised if there is more than .25 inch and probably much less difference on the brackets. Any length you set them to, somebody is going to say you did it wrong and that you should center the wheel at ride height except for those people who tell you to center the wheel in the wheel wells at full bump and then the ones that say just to center the bump stops!

In the end, I set right about 16.0 inches on my lowers, front and rear (and my fronts are a skosh longer perhaps), and I arrived at this setting by cycling my axles up and down and trying to get my bump stops to contact (remember, the rear axle is rotated, at least mine is, so the bump stops will not actually center) each other and then observe that my axle was approximately centered with the axle at full bump. I also check wheelbase at ride height, WOW, to be 93 inches.

Mine looks not unlike yours and I assure you that my bump stops contact and that my axles are square to each other and to the frame. I think there is something going on there as I have seen this exactly on several other Jeeps, as if that cup were welded at a different angle. You know what, this is not a place for people like me, and possibly you, that expect everything to be EXACT. I do not really buy into all the Jeeps being different, only that there might be more than one solution, one way to skin a cat, so they say.

J
 
Discussion starter · #6 ·
This morning I took out the old RC fixed CA's that originally came with the 4 inch lift. I measured the straight line distance from bolt to bolt and it is 16.25 inches. The tech at RC told me 15.25 in an email. SO frustrated! Ultimately my fault for not verifying. Going to set them at 16.25. Jeep handled good at this distance until the bushing failed.
 
#7 ·
16.25 is what I have with 3.25 inches lift. The RC 2.5 progressive coils have a pretty decent free length so with 3/4 spacer, it worked out great. Lifted TJ's with stock lowers seem to have the wheel and tire in the wheel well, front. Even my old RE fixed arms were 16.25 for up to 4 inches lift- I know every jeep is different but start with 16.25 for the lowers unless you have a mount that is tweaked- square up the difference and then move on to uppers. Glad u go it fixed! Those are the wrong numbers for those coils.

Same lower number should be a good place to start for rear lowers FYI. Adjust accordingly if u have SYE.
 
#8 ·
I dug out the instructions that came with the savvy/currie kit, and it looks like their starting points for all lowers was 15.75" center to center. I had to run them all out a bit to get the axles lined up. Not sure where I ended up, but 16.25 sounds about right. After the initial length adjustment, I never measure them again. I only measured the axle positions.
 
#9 ·
aparke4 said:
16.25 is what I have with 3.25 inches lift. The RC 2.5 progressive coils have a pretty decent free length so with 3/4 spacer, it worked out great. Lifted TJ's with stock lowers seem to have the wheel and tire in the wheel well, front. Even my old RE fixed arms were 16.25 for up to 4 inches lift- I know every jeep is different but start with 16.25 for the lowers unless you have a mount that is tweaked- square up the difference and then move on to uppers. Glad u go it fixed! Those are the wrong numbers for those coils. Same lower number should be a good place to start for rear lowers FYI. Adjust accordingly if u have SYE.
Click to expand...
All the RE fixed lower arms I've seen are 16" not 16.25"??
 
#13 ·
unlimited4x4 said:
I adjusted the lower ... rear CA's today to 16.25". Much better! Thanks for all the replies!
Click to expand...
why did you lengthen the rear lowers? all that does is push your axle housing into your gas tank and push your tires into your tub.

if anything, you want the rear lowers shorter than stock.
 
#14 ·
The front recipe is 16-16 1/4" lower and 15- 15 1/4" upper. There is a track bar problem for anything longer. the rear can goto 16" max with rear lower quarter triming even with a 33. Upper will be around 13.5-14" w/sye depending on pinion angle. Using currie links in the rear i have to set @ 15.5-6 to keep from over extending the upper and fit the tires when stuffed.
 
Discussion starter · #15 ·
I pushed the rear lowers out for 2 reasons. One, at 15.25 it drove horrible . I had them on for a week and the whole rear end felt wrong during acceleration, in turns etc. Second, I originally had the RC fixed arms for the 4 inch lift. The jeep performed great with these arms until the bushing failed. The straight line distance from eye to eye on the old arms was exactly 16.25. It only made sense to set the rears at 16.25 like the old arms.
 
#16 ·
On the front as you get longer on the lowers the angle increases between the frame side track bar mount and the axle side mount. This can result in the track bar hitting the differential cover. And there is more to it than just having more bend in the track bar since there are other things, drag link, tie rod link and all that good stuff moving in a vertical plane just front of the track bar.

On the rear as you get longer with the lowers the possibility increases that the track bar and track bar extension mount will hit the fuel tank skid plate. This seem to become more likely for those running a double carden type shaft that requires rotating the differential pinion up to point at the transfer case output.

And that is how I came to be approximately 16.0 inches, oddly, as I adjusted them to accomplish the above and have good pinion angles and as long of a wheelbase as I could, 16.0 is what I got, wonder how that happened. In my case, I have DA uppers, so once I had everything clearing and looking right, I then set my final pinion angles and on the front, I cheated a skosh forward (last down time) since my Currie track bar and Curreclync steering seemed to allow it.

Wheelbase, at 15.75 my wheelbase at ride height, WOW, was short of 93 inches. At 16 inches, it is close enough to the factory. Does this matter? I do not know--- see, I told you that no matter what you did, it would be wrong!

J
 
#18 ·
kaybone said:
When you all say your lowers are at 16" or 16.25' how are you measuring that exactly to get that distance? From bolt hole to bolt hole on-center?
Click to expand...
On center.
 
#19 ·
You need to worry about fitment, not wheel base.

For example, a re 5.5" long arm will be set around 92" @ ride height or we have parts crashing together and tires rubbing things at full stuff.
 
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