Adjustable Rear Control Arm Lengths for 3.25" Lift

[mphilleo]

Hi folks, long time lurker, first time poster here. I appreciate all the resources and information you've made available to us Jeepers.

I'd like to lean on you folks for some input. Long story short, I have a 2012 JKU with a 3.25 RC lift (installed by previous owner). I've done a lot to correct the issues of the cheap lift, but now I'm at the point of installing adjustable rear control arms to correct axle angle and centering in the wheel well. I got to that point when my bulging rear springs started rubbing on my adjustable rear track bar after I put on new shocks and a Hellwig sway bar.

Because I liked the quality of my Rancho geometry correction brackets up front, I went with Rancho adjustable rear control arms (RS66157B and RS66158B). I've read the instructions but there's only a note on how far you can extend the arms, but not where you should be based on lift height. I can find better info from Synergy or Metalcloak but I'm not sure if I can use those specs. I did reach out to Rancho and they didn't have the specifications I was looking for. Has anyone here who's done this before or familiar with Rancho help me out?

I'm also a little new to measuring pinion angle, but I do want to make sure I get that right. I'll pick up a magnetic angle finder to do that if anyone would be willing to chime in on some pro tips. I've included a picture of my axle as it currently as a reference.

 

[WJCO]

Hi folks, long time lurker, first time poster here. I appreciate all the resources and information you've made available to us Jeepers.

I'd like to lean on you folks for some input. Long story short, I have a 2012 JKU with a 3.25 RC lift (installed by previous owner). I've done a lot to correct the issues of the cheap lift, but now I'm at the point of installing adjustable rear control arms to correct axle angle and centering in the wheel well. I got to that point when my bulging rear springs started rubbing on my adjustable rear track bar after I put on new shocks and a Hellwig sway bar.

Because I liked the quality of my Rancho geometry correction brackets up front, I went with Rancho adjustable rear control arms (RS66157B and RS66158B). I've read the instructions but there's only a note on how far you can extend the arms, but not where you should be based on lift height. I can find better info from Synergy or Metalcloak but I'm not sure if I can use those specs. I did reach out to Rancho and they didn't have the specifications I was looking for. Has anyone here who's done this before or familiar with Rancho help me out?

I'm also a little new to measuring pinion angle, but I do want to make sure I get that right. I'll pick up a magnetic angle finder to do that if anyone would be willing to chime in on some pro tips. I've included a picture of my axle as it currently as a reference.

On the rear, you just want the pinion and the driveshaft parallel to each other and pointed at each other. Now if you've achieved that and your springs are hitting something, then you have something else going on most likely.

 

[wayoflife]

Being that you have a factory drive shaft, there is no need to set your pinion. If you had an aftermarket u-joint style double cardan shaft, you would set the pinion to be in line with the drive shaft. As far as lower arms go, you need to remember that your axle travels in an arc. As in, while your tires may not "look" centered, they will be at a full stuff. Any correction you make by adding length to your lower arms needs to be minute. For 3.25" of lift, you may only need a 1/4" of additional length at most. Any more than that and your axle will be too far back. More than likely, your coils are hitting the track bar because your upper arms are set too long.

 

[mphilleo]

Thanks for the feedback, I really appreciate it.

Based on what @WJCO said, my pinion angle looks pretty good. My goal with these arms is twofold. One, I'd like to correct the bowing on my coil springs in their perches to avoid contact with the trackbar (there's a bad picture below to show you the angle). The second goal is to help get the ride closer to stock and help with any dog tracking in the rear axle due to changes in the geometry from the lift. Based on what you see, can you guess if I'd still need correction wedges or if I can get some clearance with the control arms?

 

[wayoflife]

I should note that in your first pics, your pinion looks to be set too high. Also, is it safe to assume you do not have a rear track bar relocation bracket installed? If not, I would recommend one as that will help correct your track bar angle and that should help whatever you're feeling in the rear.

 

[fiend]

Your pinion looks to me like it’s pointed up, at a steeper angle than the driveshaft. Using longer lower arms will help address that. As Eddie says, they don’t need to be a whole lot longer. Somewhere between 1/4” and 1/2” should suffice. Since yours are adjustable, you can tinker until it’s right. If you still have problematic coil bowing, wedges are a cheap solution. Synergy makes some, as probably do others.

 

[mphilleo]

I should note that in your first pics, your pinion looks to be set too high. Also, is it safe to assume you do not have a rear track bar relocation bracket installed? If not, I would recommend one as that will help correct your track bar angle and that should help whatever you're feeling in the rear.

Sorry, those pictures didn't show everything. Here's a couple of better pictures. The lift did come with a relocation bracket. Initially the track bar was actually in the top hole, but I brought it down to the correct one (at least I believe it is) for my lift height. Thanks for the suggestions on adjustment, @fiend . It'd be nice to not have to jack up the rear differential to refill after an oil change. That does confirm my thoughts, see what I can do with these control arms and then use wedges if necessary.

General question: the Jeep is already aligned, but rear alignment shouldn't be necessary after I install these arms as long as the arms are equal lengths on both sides, right?

 

[wayoflife]

Sorry, those pictures didn't show everything. Here's a couple of better pictures. The lift did come with a relocation bracket. Initially the track bar was actually in the top hole, but I brought it down to the correct one (at least I believe it is) for my lift height. Thanks for the suggestions on adjustment, @fiend . It'd be nice to not have to jack up the rear differential to refill after an oil change. That does confirm my thoughts, see what I can do with these control arms and then use wedges if necessary.

General question: the Jeep is already aligned, but rear alignment shouldn't be necessary after I install these arms as long as the arms are equal lengths on both sides, right?

Ideally, you want your track bar to sit parallel to your axle or close to it. Looking at your pic, it's still sitting at a measurable angle. I think it was right before.

Again, being that you have a factory rear drive shaft, set the pinion angle so that it sits parallel to the output shaft on your transfer case. That's how it's designed to work from the factory. The shaft is plenty long enough to not be a problem with this. That will correct your spring bow.

No alignment is needed in the rear and the front can ONLY be aligned IF you have adjustable components. If you don't and I don't think you do, you just paid to have your steering wheel centered.

 

[mphilleo]

Ideally, you want your track bar to sit parallel to your axle or close to it. Looking at your pic, it's still sitting at a measurable angle. I think it was right before.

Again, being that you have a factory rear drive shaft, set the pinion angle so that it sits parallel to the output shaft on your transfer case. That's how it's designed to work from the factory. The shaft is plenty long enough to not be a problem with this. That will correct your spring bow.

No alignment is needed in the rear and the front can ONLY be aligned IF you have adjustable components. If you don't and I don't think you do, you just paid to have your steering wheel centered.

Great information in this post, thanks @wayoflife ! I will fix the trackbar position this weekend - what you're saying makes sense. I think the directions for that relocation bracket weren't very clear.

I'd be very happy to not throw an additional $90 at the alignment shop. They already did whatever adjustment earlier with the adjustable front and rear trackbars to help correct thrust angle...hopefully I'll still be able to get the rear trackbar into the correct eye of the relocation bracket without having to mess with the length.

While we're on the topic of thrust angle, is 1/16" or .049° difference in front to rear axle alignment a big deal? I'm guessing that should be within tolerance.

 

[mphilleo]

It's a beautiful 72° out, great weather for wrenching on my Jeep. I was doing a sanity check before correcting the rear trackbar position as suggested earlier. Here's a picture from the RC instructions. Now I'm confused which position is correct.

 

[wjtstudios]

Ideally, you want the track bar pretty level as compared to the axle. Also check how centered the rear axle is on the jeep. If it pulls to far to the passenger side, your DS can make contact with the gas tank skid

 

[fiend]

If you don’t have an adjustable track bar, pick the hole that best centers the axle at ride height. If you do have an adjustable track bar, pick the hole that makes the track bar most level with the ground, then adjust the length as necessary to center the axle side to side.

 

[mphilleo]

I figured I'd follow up and let everyone know how things went. Thread updates aren't always a guaranteed thing. This weekend, I got the adjustable upper and lower rear control arms installed. Since most folks seemed to suggest 1/4-1/2", I split the difference at 6/8" in additional length on the lowers.

I tried to keep the uppers short as possible, but had to add about 1 to 2 eighths of an inch on the uppers to make them fit (I can check my notes for specifics). As a result, I succeeded in extending the wheelbase and centering the wheel in the wheel well. Unfortunately, I don't think I dropped the pinion angle much, if at all. The springs are still somewhat bowed and the axle is still tilted.

Is there a way I can shorten the uppers and still get them to bolt to the frame and axle, so I can drop some of the pinion angle? I'm assuming I might need to creatively use my jack or remove the wheels. Either way, I am curious to see if the changes made improve or detract from the ride quality. There's a couple updated picture below.

 

[Seahawkfan]

I figured I'd follow up and let everyone know how things went. Thread updates aren't always a guaranteed thing. This weekend, I got the adjustable upper and lower rear control arms installed. Since most folks seemed to suggest 1/4-1/2", I split the difference at 6/8" in additional length on the lowers.

I tried to keep the uppers short as possible, but had to add about 1 to 2 eighths of an inch on the uppers to make them fit (I can check my notes for specifics). As a result, I succeeded in extending the wheelbase and centering the wheel in the wheel well. Unfortunately, I don't think I dropped the pinion angle much, if at all. The springs are still somewhat bowed and the axle is still tilted.

Is there a way I can shorten the uppers and still get them to bolt to the frame and axle, so I can drop some of the pinion angle? I'm assuming I might need to creatively use my jack or remove the wheels. Either way, I am curious to see if the changes made improve or detract from the ride quality. There's a couple updated picture below.

Curious you keep mentioning ride quality. What are you noticing on ride quality in the rear? You look to have an after market sway-bar back there. And if it's RC maybe that is part of your problem.

 

[mphilleo]

Curious you keep mentioning ride quality. What are you noticing on ride quality in the rear? You look to have an after market sway-bar back there. And if it's RC maybe that is part of your problem.

I replaced my stock unit with a Hellwig sway bar. I'm actually pretty pleased with the quality of the piece overall. It has tightened up the handling and ride a decent amount.

After taking the Jeep to work today, I'll make a tentative statement that bringing the wheel base back to where it should be has improved the handling and tracking. It appears to be less "fidgety or twitchy" or more true in its tracking. The wind was pretty calm this morning, so I'll have to drive it again in the wind to see if it actually helped.

I'm left with a couple questions. Now that I've centered the axle, what is the best way to rotate the pinion downward a couple degrees while maintaining the improved wheelbase? Is it possible to get rotation downward on the pinion so I can shorten up the upper control arms? Otherwise, would I be better off just leaving it alone and installing coil spring correction wedges to correct the spring bow?

 

[fiend]

I replaced my stock unit with a Hellwig sway bar. I'm actually pretty pleased with the quality of the piece overall. It has tightened up the handling and ride a decent amount.

After taking the Jeep to work today, I'll make a tentative statement that bringing the wheel base back to where it should be has improved the handling and tracking. It appears to be less "fidgety or twitchy" or more true in its tracking. The wind was pretty calm this morning, so I'll have to drive it again in the wind to see if it actually helped.

I'm left with a couple questions. Now that I've centered the axle, what is the best way to rotate the pinion downward a couple degrees while maintaining the improved wheelbase? Is it possible to get rotation downward on the pinion so I can shorten up the upper control arms? Otherwise, would I be better off just leaving it alone and installing coil spring correction wedges to correct the spring bow?

To tip the pinion down you need shorter upper arms, longer lower arms, or some combination thereof.