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Adjustable Control Arms

U

Ulver44

NAXJA Forum User
Location
nc
Is there any reason to have adjustable upper control arms rather than adjustable lowers? I was thinking of getting just one adjustable set to correct caster and save money.

I am trying to decide between a used set of street driven RE3715 SuperFlex adjustable lowers http://www.rubiconexpress.com/Jeep/XJ/Product.aspx?part=RE3715
for $148

OR

IronRockOffroad's adjustable lowers (or uppers if that's preferable) http://www.ironman4x4fab.com/Jeep_XJ_Control_Arms/XJ_LCA%28F%29.html

They don't seem to have the same flex joints so does anyone know if one is better than the other? I'm also wondering if clearance would be an issue with either since my stock control arms are definitely limited in droop because of axle contact.

Regardless of which adjustable arm set I go with, for the other two I will probably go with the cheapest IRO fixed arms. Will that be ok? I just dont want to rip my mounts off because of not having flex joints, but I'm on a tight budget.
 
You can adjust pinion/caster angles with either uppers or lowers. If you use both you can also move the whole axle forward which will give you better travel and a smoother ride. If you are going to do just one set then aftermarket lowers are preferable, usually they are stronger and will rotate better than the stock LCAs.
 
ehall said:
You can adjust pinion/caster angles with either uppers or lowers. If you use both you can also move the whole axle forward which will give you better travel and a smoother ride. If you are going to do just one set then aftermarket lowers are preferable, usually they are stronger and will rotate better than the stock LCAs.
Click to expand...

I was hoping I could move the axle forward by just getting an inch or so longer fixed arms than required for my lift which is V8 ZJ coils, 2" coil spacers and double coil isolators. I don't plan on lifting it any further.

Going by the chart at the bottom of this page: http://www.yuccaman.com/jeep/re_db.html would a 15.75" fixed upper arm be ideal in my case to move the axle forward?
 
The two angles you have to worry about are the pinion angle and the caster angle.

The pinion angle needs to be set so that the pinion points directly at the transfer case in-line with the driveshaft. Specifically, the lower u-joint (by the axle) is supposed to be straight so that it doesn't oscillate very much, and the two u-joints that are close together (on top) are supposed to oscillate in phase. If the pinion isn't at the right angle then the lower u-joint will have to oscillate, which will cause the whole front driveshaft to vibrate, make noise, eat u-joints, etc.

Meanwhile the caster angle should also to be at or near the factory angle, since that is how the steering is setup. Rotating the axle causes the inner Cs to be rotated, which causes the ball-joints to get out of alignment. This can result in excessive wear on the joints and tires, funny steering that doesn't handle properly, and other kinds of issues.

However the Jeep solid axle has the pinion and caster angles fixed relative to the axle rotation, so changes to one cause changes to the other. When you lift the jeep, the body relative to the axle is also changed. If you rotate the axle to correct the pinion angle then the caster angle is also changed and made wrong. Likewise if you set the caster angle to stock angle then the pinion angle will also be wrong.

What you have to do is find the best angle that does not produce a lot of driveline vibrations but is also bearable to steer. The FSM says to favor the pinion. In my case I was able to split the difference so both of them are "off" by about 2 degrees but neither of them is particularly bad. With your amount of lift this might not be very much at all and you might even be able to set the pinion and still be within the spec range for caster, or close enough that you don't notice. If you spend all your time in 2WD then you might want to just set caster and risk driveline vibrations when you are going slow in 4WD.

The chart you linked to (and all of the other copies of it) are only for caster angle and produce completely unbearable pinion angles. It's not really useful.
 
ehall said:
The two angles you have to worry about are the pinion angle and the caster angle.

The pinion angle needs to be set so that the pinion points directly at the transfer case in-line with the driveshaft. Specifically, the lower u-joint (by the axle) is supposed to be straight so that it doesn't oscillate very much, and the two u-joints that are close together (on top) are supposed to oscillate in phase. If the pinion isn't at the right angle then the lower u-joint will have to oscillate, which will cause the whole front driveshaft to vibrate, make noise, eat u-joints, etc.

Meanwhile the caster angle should also to be at or near the factory angle, since that is how the steering is setup. Rotating the axle causes the inner Cs to be rotated, which causes the ball-joints to get out of alignment. This can result in excessive wear on the joints and tires, funny steering that doesn't handle properly, and other kinds of issues.

However the Jeep solid axle has the pinion and caster angles fixed relative to the axle rotation, so changes to one cause changes to the other. When you lift the jeep, the body relative to the axle is also changed. If you rotate the axle to correct the pinion angle then the caster angle is also changed and made wrong. Likewise if you set the caster angle to stock angle then the pinion angle will also be wrong.

What you have to do is find the best angle that does not produce a lot of driveline vibrations but is also bearable to steer. The FSM says to favor the pinion. In my case I was able to split the difference so both of them are "off" by about 2 degrees but neither of them is particularly bad. With your amount of lift this might not be very much at all and you might even be able to set the pinion and still be within the spec range for caster, or close enough that you don't notice. If you spend all your time in 2WD then you might want to just set caster and risk driveline vibrations when you are going slow in 4WD.

The chart you linked to (and all of the other copies of it) are only for caster angle and produce completely unbearable pinion angles. It's not really useful.
Click to expand...

Thanks, I didn't know this. I guess I will aim for a better pinion angle since my XJ is mainly for off-road and regularly gets tached out in 4-low.

So 1" longer than stock CA's is what I will get unless anyone interjects. It would help if I knew my actual lift but my fenders are cut all to hell so that measurement is not possible. FWIW, 15.25" is the length IRO sends out for 3" of lift.

My final question is whether IRO solid joints with their tapered bushing sleeve will be ok for my uppers or if I should get flex joints for the uppers as well since I 4-wheel often. I probably don't want to pay the extra for them unless I'm going to rip my factory mounts off with fixed joints. One of my axle mounts is already cracked and needs welding (3 out of my 4 control arms are also mangled to hell).
 
Last edited:
RCP Phx said:
Measuring lift height........ 1" longer arms will most likely be to much!
http://www.naxja.org/forum/showthread.php?t=912893
Click to expand...

Thanks for the link. According to their measurements I have 4.25" of lift, but my control arms are bent so I think the actual lift is slightly less than that.

I agree that 1" longer UCA's may be too long. The Ironman4x4 fixed UCA's for a 3" lift are only .25" longer than stock. That .25" may just bring the tire back to center though, whereas I wouldn't mind going a bit forward from stock if I can get away with it. Does anyone else run their front axle forward slightly without issue?
 
Last edited:
If you do order from Ironman4x4fab, he can make custom lengths for you, if you decide to go fixed vs the adj.
 
Unless it will noticeably limit my flex I'm going with fixed uppers and adjustable lowers, but I may email them in a bit.

BTW, for some reason I was typing IRO before when I meant Ironman4x4!
 
Last edited:
Just go adjustable upper and lower.....WELL WORTH THE MONEY. If you don't get it just right you will have your springs getting into your bumpstop, driveshaft length issues, steering issues, etc.
 
XJRN said:
Just go adjustable upper and lower.....WELL WORTH THE MONEY. If you don't get it just right you will have your springs getting into your bumpstop, driveshaft length issues, steering issues, etc.
Click to expand...

Those are issues I have now, but I'm just going to ask the manufacturer the fixed UCA length they recommend for 4" of lift and go from there. The more you lift the more it pulls the axle backward. The main issue for me is my 33x12.5's stuffing into the inner rear of the fender plus my driveshaft looks compressed at ride height. I think the further forward the better for me as long as my bumpstops dont hit the coil.
 
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