How to Replace Control Arm : Step-by-Step Guide

Hearing a worrying clunk from your suspension and facing a control arm replacement? This is a major job, but with the right tools and knowledge, it can be done at home.

Replace control arm involves safely lifting the vehicle, removing the wheel, separating the ball joint, unbolting the old arm from the frame, and installing the new part before getting a professional wheel alignment.

As a manufacturer of control arms and other chassis parts for over 25 years at GSW Autoparts, I want to provide a clear, realistic guide. This is not a simple task for a beginner. It requires proper tools and a strong focus on safety. A mistake here can have serious consequences. This guide is for the confident home mechanic who understands the risks and is properly equipped for the job.

How to replace control arm? A step-by-step guide

Ready to tackle the job of replacing a worn control arm? This is an advanced DIY task, but following a structured process is the key to doing it safely and successfully.

The process involves preparation, lifting the car, disconnecting the old arm’s mounting points at the ball joint and frame, installing the new arm, and then correctly reassembling everything before a final, crucial wheel alignment.

Before you even touch a spanner, it’s vital to understand that this job can be tough. Bolts can be seized with rust, and separating joints requires significant force. From our perspective as a parts supplier, we know a quality repair starts with a quality process. Let’s walk through the steps.

Step 1: Preparation – Tools and Safety First

This is the most important step. Gather all your tools before you start. You will need a good socket and spanner set, a torque wrench¹, a breaker bar for stubborn bolts, a trolley jack, and, most importantly, sturdy axle stands. For the job itself, you will almost certainly need a ball joint separator tool². Do not even attempt this job without one. Your safety equipment should include gloves and safety glasses.

Step 2: Lift the Vehicle and Access the Control Arm

Park the car on a solid, level surface. Loosen the wheel nuts on the corner you’ll be working on before lifting the car. Use your trolley jack on the vehicle’s designated jacking point and lift it high enough to get an axle stand underneath at a secure point on the frame or subframe. Lower the car onto the axle stand. Never work on a car supported only by a jack. Remove the wheel to get clear access to the suspension assembly.

Step 3: Remove the Ball Joint

Locate the ball joint where the control arm connects to the steering knuckle. Remove the castellated nut and cotter pin (or the nyloc nut). Now, you need to separate the tapered stud of the ball joint from the knuckle. This joint is pressed in tightly and will not come apart by just pulling. Use your ball joint separator tool—either a "pickle fork" style separator or a press-style one—to pop the joint free. This can take a lot of force and often makes a loud bang when it separates.

Step 4: Disconnect the Control Arm from the Frame

Now locate the bolts that hold the control arm’s bushings to the vehicle’s subframe. There are usually two of them. These can be very tight and may be seized, so you will likely need your breaker bar to get them moving. Note their orientation and remove them completely. The control arm should now be free from the vehicle.

Step 5: Compare Parts and Install the New Control Arm

Take your new control arm—and this is where using a quality part like one from us at GSW really matters—and compare it side-by-side with the old one. Make sure all the mounting points, shapes, and sizes are identical. A quality part ensures a perfect fit. Manoeuvre the new arm into position and loosely install the bushing bolts and the ball joint nut. Do not tighten them fully yet.

Step 6: Reinstall the Wheel and Perform Final Checks

Here’s a critical pro tip: The bushing bolts³ must only be fully tightened when the suspension is at its normal ride height. Use your trolley jack to raise the suspension assembly to simulate the car being on the ground. Once it’s at the correct height, use your torque wrench to tighten the bushing bolts and the ball joint nut to the manufacturer’s specified torque settings. Reinstall the wheel, lower the car, and tighten the wheel nuts. The final, mandatory step is to take the car for a professional wheel alignment⁴. Your alignment will be incorrect after this job, and skipping this step will lead to poor handling and rapid tyre wear.

Does the replacement process differ for various suspension types?

Thinking all control arm replacements are the same? The complexity of the job can change significantly depending on whether your car has a MacPherson strut or a double wishbone suspension system.

Yes, the process differs. A common MacPherson strut setup has only a single lower control arm that is relatively straightforward to access. A double wishbone system has both an upper and a lower arm, making the job more complex.

As a comprehensive supplier, our GSW catalogue covers parts for all types of suspension designs, so we’re very familiar with the differences. The fundamental steps of separating ball joints and unbolting the arm are similar, but the layout and number of components can vary. A MacPherson strut system, common on most front-wheel-drive cars in the UK, is generally the simpler of the two. The strut assembly acts as the upper pivot, so you only have to deal with the lower control arm.

A double wishbone suspension, found on many rear-wheel-drive, performance, and commercial vehicles, is more complicated. It features two separate control arms—an upper and a lower—that sandwich the steering knuckle. This design offers better handling and control but means there are more components in a tighter space. Replacing an upper control arm often requires working around the strut or shock assembly, while the lower arm can have more connections to things like sway bars. Knowing which system your car has is vital before you start.

Conclusion

Replacing a control arm is a challenging but achievable job for an experienced DIYer. Prioritising safety, using the correct tools, and always finishing with a professional wheel alignment are the keys to success.