Understanding the Control Arm

What is a  control arm and how do they go bad?

A control arm, also known as an A-arm or wishbone, is a component of the suspension system. It is a sturdy, triangular-shaped arm that connects the wheel hub assembly to the vehicle’s frame or subframe. The arms are typically found in pairs, with one for each wheel, and they are designed to absorb the forces exerted on the tires during acceleration, braking, and cornering maneuvers.

How many control arms are there in a vehicle?

Back in the 50’s and 60’s all cars and trucks were build using a short-arm/long-arm (SLA) style suspension. Each of the front wheels was connected to the frame using an upper and lower arm and each contained a ball joint. In addition to the arms, the suspension contained a coil or leaf spring and a shock absorber.

In later years, the McPherson strut style suspension became popular because it offered a stiffer and more responsive feel. As you can see in the images below, this eliminated the need for the upper control arm, which saved carmakers money.

Functionality of Control Arms

Up/down movement

In addition to serving as the mounting point of the steering knuckle to the frame of the vehicle, the bushings allow the arm oo move up and down as it hits bumps in the road.

Wheel Alignment

One of the primary roles of control arms is to maintain proper wheel alignment. Misaligned wheels can lead to uneven tire wear, reduced fuel efficiency, and compromised handling characteristics.

Absorbing Road Impacts

As your vehicle navigates over bumps, potholes, and uneven terrain, the control arms act as shock absorbers, cushioning the impact and preventing excessive stress on the vehicle’s frame and occupants. They work in conjunction with other suspension components, such as shocks and struts, to provide a smooth and comfortable ride.

The control arm bushing

The control arm bushing consists of a steel sleeve surrounded by cushioning rubber. Over time and use, the rubber tends to dry and crack, reducing its ability to absorb road shock.

The bushing can be replaced by removing the control arm and using a press to push the old bushing out and pressing a new bushing in. This is not done often because the labor costs to replace the bushing can be more than the cost of a new control arm.

Examples of cracked control arm bushings

Cracked versus torn bushings

As you can see in the images above, it’s not uncommon for bushings to crack over time. But cracking alone is not a reason to replace the bushing or the arm. They can continue to do their job for many thousands of miles after cracking. However, if the rubber tears, as shown below, the bushing must be replaced or a new arm installed.

Example of a torn control arm bushing and a replacement bushing

Signs of Worn or Damaged Control Arms</h3>

Like any other automotive component, the bushings and the ball joint can wear out over time.

In addition, the arm can rust from road salt and become weak or bent.

Here are some common signs that may indicate worn or damaged bushings or ball joints

Clunking or Rattling If you hear clunking or rattling noises coming from the suspension area while driving over bumps or during turns, it could be an indication of worn bushings or ball joints within the control arm assembly.

Uneven Tire Wear

Worn or damaged bushings or ball joints can lead to improper wheel alignment, resulting in uneven tire wear patterns. This not only compromises handling but also decreases tire life, leading to premature replacement.

Steering Issues

If you notice excessive play in the steering wheel or a general lack of responsiveness, it could be a sign of worn bushings or ball joints, which can affect steering precision and handling.

©, 2024 Rick Muscoplat