Adjustable upper control arms fine-tune caster after a lift. Essential at 4.5"+ to keep the steering self-centering and prevent wandering.
Stock XJ uppers are stamped steel with rubber bushings, fixed length. After a 3" lift you lose ~1.5 degrees of caster; at 4.5" you lose ~3 degrees. Below ~3 degrees of caster, the steering won't self-center properly and the rig wanders on the highway. Adjustable UCAs let you change length to recover caster.
Brand options: IRO HD adjustable UCAs ($230/pair, johnny joint or poly), RockKrawler X Factor ($280/pair), Clayton ($280/pair), Synergy ($260/pair). The IRO and Clayton are the most common.
Note that caster can also be corrected with offset ball joint sleeves ($80/pair) — this is the cheap method that works for 3" lifts. For 4.5"+ you generally want adjustable UCAs because the offset sleeves run out of correction range.
Install is bolt-in. After install, set the length to achieve 4-5 degrees of positive caster at ride height. Verify with an alignment shop or DIY with a digital level. Adjusting UCAs also affects pinion angle slightly — set caster first, then re-verify pinion angle.
| Part | Vendor | Est. price |
|---|---|---|
| IRO HD adjustable UCAs (pair) | Iron Rock Off Road | ~$230 |
| Clayton adjustable UCAs | Clayton | ~$280 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.