Jeep WJ Grand Cherokee Rear A Arm Install -- Core 4x4 Crawler Series

Spence and Gabby install the Core 4x4 Crawler Series adjustable rear upper A arm on a lifted WJ Grand Cherokee. Covers removal of the factory arm, bracket install, pinion angle setup, torque specs, and the re-torque process.

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The factory upper rear A arm on the 1999–2004 Jeep Grand Cherokee WJ uses a rubber ball joint that wears out over time and limits your suspension travel. If your WJ is lifted, the factory arm cannot recenter the rear axle or correct the pinion angle — and the stock ball joint is already maxed out at ride height. The Core 4x4 Crawler Series adjustable rear upper A arm replaces the factory piece with a fully adjustable arm featuring Johnny Joints at both the body and axle side, giving you the range to dial in your pinion angle and axle position without limiting down travel.

In this video, Spence and Gabby from Core 4x4 walk through the full install on a lifted WJ in the shop. This is a straightforward job — three bolts on the bracket, a body-side bolt, and some finessing to get the old arm out around the brake lines and breather hoses. The biggest trick is setting the arm length and pinion angle on the ground after torquing everything in the air.

Fitment: Jeep Grand Cherokee WJ 1999–2004 | Core 4x4 Crawler Series Adjustable Rear Upper A Arm (CRL-J-WJ-AA1)

Spence and Gabby from Core 4x4 standing in front of the silver Jeep Grand Cherokee WJ on the lift before the rear upper A arm install

Why Replace the Factory WJ Rear Upper A Arm?

The factory upper rear A arm on the WJ uses a rubber ball joint at the axle end. On a stock-height Jeep, the joint is already near its range limit. Once you add a lift — even two or three inches — the ball joint is maxed out. That creates two problems:

No down travel: The factory ball joint is already at full extension at ride height, so any droop is fighting the joint. The suspension cannot travel down freely, which means less articulation off-road and a rougher ride on the street.
No adjustability: The factory arm is a fixed length. You cannot change the pinion angle or recenter the axle after a lift. If your driveshaft has a vibration at highway speed, the pinion angle is likely the cause — and you cannot fix it without an adjustable arm.
Wear and age: Older WJs leak fluids on everything (as Spence puts it, it would not be a Jeep if it did not leak). The rubber ball joint degrades over time, leading to slop in the rear axle and unpredictable handling.

Under the WJ Grand Cherokee showing the factory rear upper A arm area with worn rubber ball joint and aging suspension components

The Core 4x4 Crawler Series A Arm

The Crawler Series adjustable rear upper A arm is a direct replacement for the factory piece. Here is what you get:

Johnny Joints at both ends — body side and axle side. These are spherical rod ends that rotate freely in every direction, handle serious loads, and do not limit suspension travel the way a rubber ball joint does.
Adjustable length — the arm threads in and out so you can fine-tune your pinion angle and axle centering without removing the arm from the truck.
Multi-hole bracket — the axle-side bracket has multiple mounting holes, so you can pick the bolt position that gives you the best combination of lift height and travel range.
Independent crush sleeves — you can torque everything in the air (at full droop on the lift) without creating bushing preload. When you lower the Jeep, the sleeve settles to its natural position.

Core 4x4 Crawler Series rear upper A arm on the workbench next to the worn factory arm, showing the Johnny Joint vs the maxed-out factory ball joint

Removing the Factory Arm

With the WJ on the lift at full droop, start by removing the three bolts on the axle-side bracket. This is the easiest way to get at the arm because the upper bushings have a lot of binding when the suspension is drooped. Once the bracket is off the axle, disconnect the brake lines and breather hoses from the arm — they are clipped to it.

Tip: Finessing the factory arm out can be tricky if you are working on the ground. Spence recommends doing it on a lift or at least with the Jeep high on jack stands so you have room to rotate the arm out past the differential and brake components.

Spence under the WJ pointing at the factory rear upper A arm during removal, showing the three bracket bolts and brake line routing

Installing the New Arm

Step 1: Install the Bracket and Body-Side Bolt in the Air

With the factory arm out, bolt in the new Crawler Series arm. The axle-side bracket goes on first — torque it down while the Jeep is still on the lift. You can also torque the body-side Johnny Joint bolt in the air. Because Johnny Joints have independent crush sleeves, torquing at full droop will not create preload. The sleeve is not fused to the joint, so it settles freely once the Jeep is back on the ground.

Step 2: Route Brake Lines and Breather Hoses

Zip-tie the brake lines and breather hoses to the new arm to keep them up and out of the way. The factory clips will not fit the new arm, but zip ties work fine and keep everything routed cleanly.

Spence bolting the new Core 4x4 Crawler Series blue rear upper A arm into the WJ with the new bracket and Johnny Joints visible

Step 3: Set Pinion Angle and Bowl Height on the Ground

This is the critical step. Lower the Jeep to the ground under its own weight before doing any adjustment. You need the suspension loaded to set the pinion angle correctly.

When setting the arm, you are looking for two things:

Johnny Joint angle at the frame side: You want the joint slightly up or level so it has room to travel downward. Most of the WJ’s rear suspension travel is down travel — it does not tuck much at the upper A arm. If the joint is already angled down at ride height, you have no room to droop.
Pinion angle: The pinion should be parallel to the output shaft of the transfer case. Look at the angle of the pinion yoke and compare it to the driveshaft angle at the transfer case end. Parallel is the target.

Starting point: On this WJ with approximately a 3-inch lift, Spence used the top hole on the multi-hole bracket with the arm threaded out about half an inch. This is a good starting point for a similar setup. If you have adjustable lower rear arms and you adjust them to recenter the axle, the upper arm length and hole position will need to change as well.

Under the WJ on the ground showing the new Core 4x4 blue A arm installed with the torque body mount spec of 65 ft-lbs displayed

Torque Specs

Component	Torque Spec
Body mount bolts (12mm)	65 ft-lbs
Bracket thru bolt	12 ft-lbs
Bracket-to-axle bolts	125 ft-lbs
Jam nut	250 ft-lbs

The Re-Torque

Drive the Jeep for 150–200 miles, then get back under it and re-torque everything. This settling period allows the threads, joints, and mounting surfaces to fully seat under real driving loads. After the re-torque, the components are permanently seated and will not move again. Skipping this step is the most common reason jam nuts back off on adjustable arms.

Spence setting the pinion angle and arm adjustment on the WJ Grand Cherokee with the Jeep lowered to the ground, showing the blue Crawler Series A arm and multi-hole bracket

Tools Required

Floor jack and jack stands (or a lift)
Socket set (metric — 12mm for body mounts, appropriate sizes for bracket and axle bolts)
Torque wrench (up to 250 ft-lbs for the jam nut)
Wrenches for Johnny Joint jam nut (large crescent wrench or pipe wrench with cheater bar)
Penetrating fluid (PB Blaster or similar — the WJ underside will be crusty)
Zip ties (for re-routing brake lines and breather hoses)
Pry bar (for finessing the factory arm out)
Paint marker (for marking jam nuts after torque)

Frequently Asked Questions

No. The Crawler Series adjustable rear upper A arm works as a stock replacement on a non-lifted WJ. It also works on lifted setups from 2 to 6+ inches. On a stock-height WJ, you get the benefit of replacing the worn factory ball joint with a Johnny Joint that rotates freely and does not limit travel. On a lifted WJ, you get the added ability to correct pinion angle and recenter the axle.

Lower the Jeep to the ground under its own weight. Look at the angle of the pinion yoke on the rear differential and compare it to the driveshaft angle at the transfer case output. The pinion should be parallel to the transfer case output shaft. Use the adjustable arm length and the multi-hole bracket to dial in the angle. On a WJ with about a 3-inch lift, the top hole with the arm threaded out about half an inch is a good starting point.

Yes, for the bracket bolts and body-side bolt. Core 4x4 Johnny Joints have independent crush sleeves, so you can torque at full droop without creating preload. However, you must lower the Jeep to the ground before setting the final arm length, pinion angle, and the bracket bolt that controls your bowl height adjustment. That last bolt should be set and torqued with the suspension loaded.

The factory rubber ball joint has a limited range of motion and is already near its max at stock ride height. Once you lift the WJ, it is completely maxed out and limiting your down travel. Johnny Joints are spherical rod ends that rotate freely in all directions, handle much higher loads, and do not limit suspension travel. They are also rebuildable and can be torqued at any suspension position because of the independent crush sleeve design.

It is critical. The settling period allows the threads, joints, and mounting surfaces to fully seat under real driving loads. After 150 to 200 miles, get back under the Jeep and re-torque every bolt and jam nut. If you paint-marked the jam nuts at install, you will be able to see if anything has moved. After the re-torque, the components are permanently seated. Skipping this step is the number one reason people have jam nuts back off.