Adjustable control arm length

Hopefully someone reads and can answer…I completely removed passenger side front UCA and then the driver front. I jacked up from driver spring mount measuring the change in angle I needed based on the alignment reports. This jacking also raised the driver side a bit. With my caster now set I installed the passenger UCA…now here’s the question, since I’ve read the arm lengths aren’t necessarily identical, should I set the front driver side with the jack still putting load on it, or with the passenger side installed, should I lower the jack, let it settle and then install driver side UCA? Note, axle is near center (1/4-1/2 at most off), and my lower control arms are fixed…. Just prefer to get right the first time!

Thanks!
 
Brian.souhan said:
Hopefully someone reads and can answer…I completely removed passenger side front UCA and then the driver front. I jacked up from driver spring mount measuring the change in angle I needed based on the alignment reports. This jacking also raised the driver side a bit. With my caster now set I installed the passenger UCA…now here’s the question, since I’ve read the arm lengths aren’t necessarily identical, should I set the front driver side with the jack still putting load on it, or with the passenger side installed, should I lower the jack, let it settle and then install driver side UCA? Note, axle is near center (1/4-1/2 at most off), and my lower control arms are fixed…. Just prefer to get right the first time!

Thanks!
Click to expand...
I do the driver side first since I normally jack under the pinion. Once it is set release the jack and then install the passenger side and remeasure to make sure I did not move anything.
 
Brian.souhan said:
Hopefully someone reads and can answer…I completely removed passenger side front UCA and then the driver front. I jacked up from driver spring mount measuring the change in angle I needed based on the alignment reports. This jacking also raised the driver side a bit. With my caster now set I installed the passenger UCA…now here’s the question, since I’ve read the arm lengths aren’t necessarily identical, should I set the front driver side with the jack still putting load on it, or with the passenger side installed, should I lower the jack, let it settle and then install driver side UCA? Note, axle is near center (1/4-1/2 at most off), and my lower control arms are fixed…. Just prefer to get right the first time!

Thanks!
Click to expand...

I hate the front axle for this reason.

With the rear, you would support the pinion with your jack and adjust the second control arm so that the bolts for both sides will freely slide in. That way you know the preload should be identical at ride height.

But in front you're forced to jack under the spring perch, which is under one side,rather than centered like the pinion, and ends up raising the axle a bit, but I have no alternative idea so I just do it that way and hope it's close.
 
Blackjack said:
I do the driver side first since I normally jack under the pinion. Once it is set release the jack and then install the passenger side and remeasure to make sure I did not move anything.
Click to expand...

How do you do that in front? With the spring perch forward of the axle centerline I've always seen the pinion want to rotate up, not down.
 
freedom_in_4low said:
How do you do that in front? With the spring perch forward of the axle centerline I've always seen the pinion want to rotate up, not down.
Click to expand...
Yeah I should have explained better. I use the jack as a stop and manipulate the axle with a bar. Maybe since I have less weight up front with the four popper mine does not move the much with the arms off.
 
  • Like
Reactions: freedom_in_4low
Yes, mine would rotate the pinion up without the jack under the perch…. So with nothing to use from center, it lifts a bit as well so just not sure if I should install other upper while still jacked or after release and let settle. I’m thinking based maybe meet in the middle??
 
mrblaine said:
Regardless of the reasons, the only thing that matters is that you wind up with similar pre-load on the arms at ride height.
Click to expand...

It's pretty clear how to accomplish this on the rear axle, but how do you get equal preload at ride height on the front axle where the jacking point is on one side (the underside of a spring perch) instead of centered (like the rear pinion)? Especially with SA arms?
 
freedom_in_4low said:
It's pretty clear how to accomplish this on the rear axle, but how do you get equal preload at ride height on the front axle where the jacking point is on one side (the underside of a spring perch) instead of centered (like the rear pinion)? Especially with SA arms?
Click to expand...
You think jacking on one side to relieve some spring load is not going to rotate the WHOLE axle forward or back?

That side, I use the tie rod as the jack point most often.
 
mrblaine said:
You think jacking on one side to relieve some spring load is not going to rotate the WHOLE axle forward or back?

That side, I use the tie rod as the jack point most often.
Click to expand...

More thinking of the way it tends to lift the side that the jack is under, so it's no longer really at ride height and making even preload there would likely create uneven preload at ride height.

@Brian.souhan The tie rod would work better since it's a longer lever, putting a better moment around the axle without picking it up.
 
freedom_in_4low said:
More thinking of the way it tends to lift the side that the jack is under, so it's no longer really at ride height and making even preload there would likely create uneven preload at ride height.

@Brian.souhan The tie rod would work better since it's a longer lever, putting a better moment around the axle without picking it up.
Click to expand...
You should not be putting that much pressure into it. It only takes a slight amount to rotate the top of the axle back until you can turn the bolt easily to show you were zero load on the bolt is.
 
Not sure why, but mine did take some pressure, and lift the front a bit, but think I have a way to get it back, let it down (but not letting jack down all the way), work out the passenger bolt, then (assuming still have enough caster left), install both sides from there??
 
Brian.souhan said:
Not sure why, but mine did take some pressure, and lift the front a bit, but think I have a way to get it back, let it down (but not letting jack down all the way), work out the passenger bolt, then (assuming still have enough caster left), install both sides from there??
Click to expand...
You really need one person checking to see if the bolt is loose in the single upper arm that is installed while another runs the jack. If you are doing it with both arms installed, that's not going to work so well.
 
mrblaine said:
You really need one person checking to see if the bolt is loose in the single upper arm that is installed while another runs the jack. If you are doing it with both arms installed, that's not going to work so well.
Click to expand...
Yes, was planning to lower with just one arm installed, try to strap the pinion down somehow to prevent it from rotating out of place, then at ride height install both arms…might not be easy, but think that should work with a few tries…just want to make sure installing them at ride height with the bolts going in easy is correct. Thanks!
 
Ok, so to finish this up, I jacked it up, then used ratchet strap to hold in place while I lowered the jack, allowing me to install both control arms under no preload then removed the ratchet strap. It relaxed more than I would have liked, so will do it again, but going from negative to 4 degrees of camber have completely changed the way it drives…can’t believe I was such an idiot to not realize what was going on with my steering! Thanks everyone for the help and this forum!
 
Hi,

My 97 TJ has a 4-inch lift but apparently no control arm changes were made when it was installed. I'm switching to Core 4x4 adjustables , the whole set.

As background, my completed LCAs had OEM lengths of 15 3/4 & the new arms are set to 16 3/8 (difference = 5/8" ) The length chart for OEM & new matches actual.

Now the UCAs: The chart provided indicates an UCA oem length of 15 in. & set length of 15" for the rear. No change. However my rear UCA OEM length as just removed from vehicle is 13 - 1/4. Thats a 1 - 3/4 " diff. Significant disparity from chart.
So for a set distance for new arms, my gut says keep the UCA at/near 13 1/4 since the specs are saying dont change the UCA length. Also I don't believe my brake lines will accommodate a 1 - 3/4" increase in length to get to the 15". Thoughts, considerations?
Alternatively is there another chart that assumes an OEM length of 13 1/4" that matches my jeep?
Ill try to measure my pinion angle tomirrow (with 1 UCA removed) if it matters.

Thanks in advance,
Blazem
 
Damn, wrote a reply and couldn’t recall password, but now properly logged in so hope this helps!

First, there are far more out there with practical experience than I, but will give you what I found.

My current lift is sitting at 3ish inches and I found my front pinion to driveline angle was initially at 0 degrees, which was bad…but had no vibrations, just when going over humps or driving on highly off camber highways due to road work, I was always fighting the steering. After adjusting camber to 4ish degrees, drives like a dream (although tomorrow want to adjust again to get to recommended 5+ degrees).

From what I read, rear is mostly about driveline vibrations…now my lift height has varried from an initial of a claimed 4.5in lift (RE 4.5in lift circa 2002) to as high as a 5.5ish lift (switched to metal cloak 4.5 in springs and sat an inch higher) to currently about a 3in lift (switched to JKS 3 in dual rate springs and actually measured height an compared to a chart which put me at 3 in lift). My rear driveline pinion angle is sitting at less than 1-2 degrees currently, and throughout all of these different heights I never had vibrations, which suggest their is some forgiveness in the rear driveline to pinion angle (note previously I never payed attention to axle center, but currently sits about perfect).

If I do get working front angle tomorrow as planned, I will measure my rear UCA length and post it, and hopefully others will provide input as well so that you can get set right. But again, from what I read, for rear the most important thing is to have as low as possible and ensuring you have no driveline vibrations.

Hope this helps and hope to add a bit tomorrow!
 
blazem said:
Hi,

My 97 TJ has a 4-inch lift but apparently no control arm changes were made when it was installed. I'm switching to Core 4x4 adjustables , the whole set.

As background, my completed LCAs had OEM lengths of 15 3/4 & the new arms are set to 16 3/8 (difference = 5/8" ) The length chart for OEM & new matches actual.

Now the UCAs: The chart provided indicates an UCA oem length of 15 in. & set length of 15" for the rear. No change. However my rear UCA OEM length as just removed from vehicle is 13 - 1/4. Thats a 1 - 3/4 " diff. Significant disparity from chart.
So for a set distance for new arms, my gut says keep the UCA at/near 13 1/4 since the specs are saying dont change the UCA length. Also I don't believe my brake lines will accommodate a 1 - 3/4" increase in length to get to the 15". Thoughts, considerations?
Alternatively is there another chart that assumes an OEM length of 13 1/4" that matches my jeep?
Ill try to measure my pinion angle tomirrow (with 1 UCA removed) if it matters.

Thanks in advance,
Blazem
Click to expand...
Do you have or did your " whole set" include adjustable track bars?
This will be important moving forward and to help you get set up.
You'll need to ditch the measurement charts for the most part and do the following-
With the jeep supported by the frame-
Remove the control arms one at a time and replace with your new ones. The initial lengths don't matter (within reason) just adjust them to get them in . One at a time. An alignment punch will be your friend. With any luck things won't move around much and they will be close. Snug the bolts, don't fully torque.
Once all 8 CAs are in - lower jeep to rest on the ground ( ride height)
Center the axles side to side by adjusting track bars as needed, push, pull, pry ratchet strap, cuss, have a beer, repeat. Or not, it might be close.
Once exactly centered side to side move on to adjusting axles longitudinally by using the adjustability in the lower arms. Without double adjustable arms this means a lot of up and down and manipulation of the axle. Front and rear to each other (tape measure) and each independently to a common spot on the frame like a skid bolt.
Once arms are in, bolts snugged, axles centered side to side, square to each other, each axle independently square to the the frame report back.
Dont worry about castor or pinon angle until the above is done.
Setting this up will teach you much about our suspensions. Double adjustable CAs make the process much easier and do come at a price but worth there weight in gold.
 
I am curious, is there an acceptable amount to center within…I know previously my center was far off and it was still driveable, but with my last set of changes my center on the axles are within an eighth to quarter inch (takes a bit more effort to get a precise measurement). What is an acceptable tolerance for axle center? Again, right now my jeep is driving great, and since only my front track bar is adjustable, curious how much I should mess around?
 
Tough to get too much better than that in my opinion given all the variables in play but others may disagree.
 
Top Bottom
Back