What Does a Control Arm Do? Signs of Wear, Failure & Replacement

Control arms are a key part of a vehicle’s steering and suspension system. They help connect the hub carrier or steering knuckle to the vehicle’s chassis or subframe, allowing the suspension to move while helping to maintain the wheel correctly positioned.

As control arms and their associated components wear, they can affect vehicle handling, wheel alignment and ride quality. Knowing the common signs of wear can help garages identify potential issues during inspection.

What does a control arm do?

A control arm connects the vehicle’s chassis or subframe to the steering knuckle or hub carrier and allows controlled movement as the suspension travels over different road surfaces.

Control arms typically incorporate bushes and may also include or work in conjunction with a ball joint, depending on the vehicle’s suspension design. These components work together to allow suspension movement while helping maintain the correct position and alignment of the wheel.

Because control arms are subjected to continual movement, vibration and road impacts, they can experience wear over time.

What are the signs of a worn control arm?

A worn or damaged control arm can cause several noticeable symptoms.

Common signs include:

• Knocking or clunking noises over bumps

• Uneven or accelerated tyre wear

• Loose or imprecise steering

• Vehicle pulling to one side

• Steering wheel vibration

• Changes in handling or stability

• Visible damage or deterioration to suspension bushes

These symptoms can also be caused by other steering and suspension components, so a complete inspection is important before identifying the control arm as the source of the problem.

What causes control arms to fail?

Control arms and their associated components can deteriorate through normal use, particularly on vehicles with higher mileage.

Common contributing factors include:

Road impacts: Potholes, kerbs and uneven road surfaces can place additional loads through steering and suspension components.

Age and mileage: Repeated suspension movement can eventually cause bushes and joints to deteriorate.

Corrosion: Exposure to moisture, road salt and contaminants can contribute to corrosion of metal components and mounting areas.

Component wear: Control arm bushes and ball joints can wear independently and affect the performance and movement of the assembly.

How should garages check a control arm?

Control arms should be inspected as part of a wider steering and suspension check.

Technicians should look for visible damage, excessive movement, deteriorated or damaged bushes, corrosion and any signs that the associated ball joint or mounting points require attention.

If a vehicle is showing symptoms such as knocking, uneven tyre wear or changes in steering feel, the complete steering and suspension system should be checked rather than assuming that one component is responsible.

Vehicle manufacturer specifications and the relevant component manufacturer’s fitting instructions should always be followed.

Do control arms need to be replaced in pairs?

Not necessarily. Replacement should be based on the condition of the individual components and the vehicle manufacturer’s requirements.

However, when one control arm has developed significant wear or damage, it is worth inspecting the corresponding component on the opposite side. Components on the same axle are exposed to similar road conditions, mileage and operating loads. Similar levels of wear may therefore be present.

Following replacement, wheel alignment should be checked where required, particularly if the removal or replacement procedure may affect the vehicle's suspension geometry.