After lots of reading I haven't found a very good answer. My '05 TJ has what I've determined to be a 4" suspension lift that was on it when I bought it. I have no idea what brand it is. All the control arm bushings are shot and need replaced. The front lower aren't factory but aren't adjustable either. From what I can tell the front upper are still factory. Reading and looking at lift kits, some include upper front arms and some don't. Some people say you need them and others say you only need lower. Ask the lifts I researched were 4". My issue is should I keep the factory length or is there a reason to go adjustable on the top? Only had the Jeep a few years and am doing all my own work on it, but I'm definitely still learning and have never dealt with a lift kit on a vehicle before.
Do I need adjustable upper control arms
- Thread starter Tomdakota
- Start date
There will be others to answer more knowledgably, but I chose to install all 8 adjustable control arms. 97 TJ with PO's 4" lift. I'll be installing the SYE kit, TCase rebuild and new front/rear driveshafts this weekend - so my thinking is that having both upper & lower adjustable control arms will help dial in the rear diff position & angle better than just having lower adjustable control arms.
Adjustable rear UCAs are primarily to adjust driveshaft angles and front UCAs are primarily for adjusting caster and to alleviate driveshaft vibrations.
IF you are installing a SYE with 4" of lift; you most certainly will need adjustable rear UCAs to adjust driveshaft to pinion angles to 0* difference.
IF you are installing a SYE with 4" of lift; you most certainly will need adjustable rear UCAs to adjust driveshaft to pinion angles to 0* difference.
The simple answer, at least for the rear, is to look at your driveshaft angle. Assuming you have an SYE, you'll want the rear diff yoke to be exactly in line with the driveshaft, like Charles said. If you don't have an SYE, you'll want the yoke on the diff to be parallel to the yoke on the transfer case. With a 4" lift and no SYE your driveshaft angle will be super steep and the u-joints will not like it...and they'll tell you about it while you're driving.
That said, with a 4" lift, you'll almost certainly need (likely already have) an SYE, which virtually guarantees you'll need adjustable upper arms. Whether or not you need adjustable lower arms...well...the truth is that changing the rear pinion angle necessarily pushes the rear axle forward or backward. The adjustable lower arms can counteract that to correctly position the axle. Whether or not you find this to be necessary/beneficial is a different topic. I think you'll find a lot of people with similar setups to you only using adjustable uppers.
That said, with a 4" lift, you'll almost certainly need (likely already have) an SYE, which virtually guarantees you'll need adjustable upper arms. Whether or not you need adjustable lower arms...well...the truth is that changing the rear pinion angle necessarily pushes the rear axle forward or backward. The adjustable lower arms can counteract that to correctly position the axle. Whether or not you find this to be necessary/beneficial is a different topic. I think you'll find a lot of people with similar setups to you only using adjustable uppers.
Yes you need adjustable control arms. Ultimately you will need your pinion to be pointed almost perfectly in-line with the drive shaft. This is expertly 
explained in the video below.
explained in the video below.
The installation process can be learned in this video. In the video they are working on a Rubicon but the concept and even the control arms themselves are the same.
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