Replacing an A-frame ball joint
A worn ball joint will cause noise and handling issues, while damage to its rubber boot will fail the MOT test. Dave Barker shows how it’s renewed
THE rear suspension upper link ball joint, or A-frame ball joint as it’s commonly called, is located on top of the rear axle. The joint is secured in a mounting block attached to the rear axle casing and to the two upper link arms (forming the A-frame) which, in turn, is secured to the chassis. The ball joint allows the axle to pivot on the A-frame.
The condition of this joint is often overlooked. On some vehicles they will last for many years without any problems, on others they tend to wear out in a short time, all depending on usage and environment. Wear is gradual and so it’s often not noticed by the driver. The result is a very loose rear-end, allowing the axle to move excessively, and a clonking sound from the rear of the vehicle.
Replacing the A-frame ball joint looks an easy job. But, being located under the vehicle, road dirt and corrosion builds up and the bolts become badly corroded, so they aren’t going to be easily undone. It’s normal for the two securing bolts to be seized in the pivot block (fulcrum bracket) and you will often need to cut off either the bolt head or the nut, and then knock the remains of the bolt out of the bracket. On the plus side, the job is now easier than in past years. Originally, the ball joint was available only as a single item, so you needed to press the old ball joint out of the pivot block and then press the new joint into place. That job required a 10-tonne hydraulic press which few people have at home. But now you can buy a complete assembly, with the A-frame ball joint already fitted into a new pivot block. Oddly, this does not come supplied with new bolts, which have to be ordered separately. This complete assembly does cost around twice the price of just the ball joint on its own, but it does make the job easier and much quicker.
Here, we’re replacing the joint on a 300Tdi Defender 90 on which the joint was showing signs of play, and the rubber boot was split. Before starting, we wire brush the exposed threads clean of rust and give all the threads and nuts a good soaking in penetrating oil.