Jeep TJ Rear Upper Adjustable Control Arms: Fitment and Selection

Define the job the arms must do

The TJ rear suspension uses coil springs with a four-link layout: two lower control arms, two upper control arms and a track bar. The upper arms run from frame brackets to brackets on top of the axle housing. When ride height changes, each link swings through an arc. That arc rotates the axle housing, which changes the pinion angle, and it can also shift the axle slightly fore and aft. Fixed-length factory arms cannot correct for this. Adjustable uppers let you lengthen or shorten the arm to rotate the axle back to the angle your driveline needs.

Start by describing your own situation. Note your lift height and whether you kept the factory slip-yoke driveshaft or changed to a slip-yoke eliminator with a double-cardan shaft, because the two styles call for different pinion targets. With a conventional single-cardan shaft, the pinion should sit roughly parallel to the transfer case output. With a double-cardan shaft, it should point roughly toward the transfer case. Also consider how the Jeep is used. A daily driver on a mild lift benefits most from quiet, vibration-damping joints, while a trail rig benefits from articulation and rebuildable hardware. If your Jeep has a modest lift and no driveline vibration, adjustable rear uppers may not be needed yet.

Check compatibility with your TJ

Confirm the vehicle first. The TJ Wrangler was built for the 1997 to 2006 model years, and the longer-wheelbase LJ Unlimited was sold from 2004 to 2006. Because the LJ's longer wheelbase changes rear link geometry, make sure the listing names your body style rather than assuming every TJ arm fits an LJ. TJs left the factory with either a Dana 35 or a Dana 44 rear axle. Check that the arms are listed for your axle, especially if the axle has been swapped or its brackets replaced or repaired.

Next, compare the arm to the mounting points under your Jeep. The bushing or joint sleeve width must match the bracket opening, and the bolt diameter must match the bracket holes. Measure your current upper arm from bolt center to bolt center, then confirm that the new arm's adjustment range covers that length with room to lengthen or shorten for your lift. Check clearance at full compression and full droop against the exhaust, brake lines and track bar. Taller lifts sometimes use frame-side or axle-side relocation brackets. These change the geometry the arms work within, so plan the brackets and arms together rather than adding one later.

Features that affect the choice

Adjuster design is the biggest convenience difference. A single-adjustable arm has one threaded end, so you usually unbolt one end and spin the joint to change length. A double-adjustable arm uses left-hand and right-hand threads, so you can rotate the arm body with the arm still installed. That makes it much easier to fine-tune pinion angle in small steps, which matters when you are chasing a vibration.

Joint type determines ride quality and maintenance. Rubber bushings are quiet and absorb driveline vibration but allow less misalignment. Polyurethane bushings feel firmer and resist deflection, but they can squeak without lubrication. Articulating flex joints allow more axle movement and can usually be rebuilt, though some transmit more noise. Rod ends offer the most articulation but pass more vibration into the body, which makes them better suited to dedicated off-road builds than daily drivers. Many arms pair a flex joint at one end with a bushing at the other as a compromise.

Judge construction by stated details, not labels. Useful information includes tube material and wall thickness, solid versus tubular bodies, threaded-end diameter, jam nut design, grease fittings and coating. Terms such as heavy-duty or maximum articulation mean little unless the manufacturer backs them with dimensions, materials and joint specifications. If you drive on salted roads, durable coatings and protected threads matter more than a slightly lighter arm.

Installation and pinion angle setup

Work on level ground with the front wheels chocked. Raise the rear with a jack under the axle and place jack stands under the frame. Keep the jack lightly supporting the axle so it cannot drop or rotate when a link is unbolted, and never work under a vehicle held up only by a jack. Replace one upper arm at a time so the remaining links keep the axle located.

Set each new arm to the length of the part it replaces, install it, then measure pinion angle with an angle finder against the target for your driveshaft type and the arm maker's guidance. Adjust both arms by the same amount so you do not twist the axle housing or preload the joints, and tighten the jam nuts once the length is set. Do the final tightening of bushing bolts with the Jeep resting on its wheels at normal ride height, using the fastener specification from the factory service information or the arm maker. Tightening rubber bushings with the suspension hanging can preload them and shorten their life.

On this solid rear axle, the upper arms mainly control pinion angle, while the lower arms and track bar govern fore-aft position and side-to-side centering. If you changed the lower arms at the same time, measure axle squareness and wheelbase on both sides or have a shop check rear alignment. Finish with a test drive at a range of speeds and listen and feel for driveline vibration.

Limitations and ownership costs

Adjustable rear uppers do not add lift and do not correct lateral axle offset, which is the track bar's job. They cannot cure vibration caused by worn universal joints, a driveshaft that is too short for the lift, insufficient slip travel or damaged brackets. If adjusting pinion angle does not resolve a vibration, inspect those parts rather than continuing to change arm length.

Plan for ongoing care. Check joint play periodically and after hard trail use, grease fittings if the arms have them, confirm jam nuts are tight and inspect threads for corrosion and bushings for cracking. Budget for rebuild kits or replacement bushings, an angle finder if you do not own one and possibly an alignment check. Some owners also find that a lift large enough to need these arms also calls for a slip-yoke eliminator or a new driveshaft, which can cost more than the arms.

Build a practical shortlist

Compare candidates against a short checklist instead of rankings. Does the listing name your body style and rear axle? Does the adjustment range cover your measured length with margin? Do you want single or double adjustment, and which joint type suits how you drive? Are rebuild parts sold separately, and do the instructions include fastener values and pinion setup guidance? Are materials, tube dimensions and coating stated, and what do the warranty terms cover? Finally, decide whether your lift also calls for adjustable lower arms or relocation brackets, so the parts you buy work together.