What Is a Control Arm?

Vital to your car’s suspension system, control arms connect the wheels to the car’s frame and allow the driver to maintain control.
Written by Abbey Orzech
Reviewed by Georgina Grant
Control arms on a car link your front wheels to your car’s frame and are some of the most vital parts of a vehicle’s suspension system.
Your vehicle’s ability to maneuver uneven terrain while maintaining control is thanks, in part, to the control arms. As key components in the overall suspension system that supports a vehicle’s weight and handling abilities, control arms and any malfunctions they may suffer are certainly something you’ll want to be aware of.
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What is a control arm?

A control arm is a mechanical component of a vehicle’s front suspension system. It is the connection between your car’s front wheel and your car’s frame that allows you to maintain control of your steering while going over bumps and road irregularities.
Control arms are usually made from stamped steel, cast iron, or cast aluminum depending on the design of the vehicle. Steel and iron will be best for sturdiness and strength, while aluminum will work wonders for lightweight vehicles.

Parts of a control arm

Depending on whether the suspension is a control arm type suspension or a strut-type suspension, the control arm itself may have an upper arm and a lower arm (control arm suspension) or just a lower arm (strut suspension). If there is just a lower arm present, the strut will function as the upper arm.
The design of the control arms varies depending on the design of the vehicle, but control arms are usually A-shaped, L-shaped, or wishbone-shaped.
There are connection points on both arms so that they may attach to the uppermost part and the lowermost part of the front wheel’s steering knuckle. Both arms will also reach back and connect to the vehicle’s frame. On the frame side, there are bolts and bushings that connect the control arm to a hinge. Connecting the control arm to the steering knuckle side is a steel spindle and ball joint.

How do control arms work?

The bushings keeping the control arm attached to the vehicle’s frame let the control arms move up and down with the shape of the road. They prevent direct metal-to-metal contact and thus protect the mechanical pieces from excessive friction and wear. They will also help make your ride more comfortable by absorbing a good amount of noise and vibration that naturally occurs during a drive. The hinge will work to keep your wheels in constant contact with the ground.
On the steering knuckle side, the steel spindle connecting the control arm to the wheel is braced by a ball joint. This ball joint is another movement-focused component that allows the front wheel to rotate left or right while the wheel is also moving up and down.
And to ensure the entire weight of the vehicle is not bearing down on the control arm from the vehicle’s frame, there is a heavy steel coil spring between the frame and arm that takes the brunt of the weight and provides cushioning when going over bumps or potholes.
All of these parts work together to allow a driver ease of handling and steering coordination when driving on anything other than a completely smooth surface—which, let’s be real, can be a rarity.

Symptoms of a bad control arm

Given the nature of the work control arms do for our vehicle’s front suspension, they are designed to withstand a lot. But just like anything else, wear and tear will eventually compromise the part’s integrity and ability to do its job.
How quickly the control arm takes on wear and tear depends on the type of driving a vehicle is subjected to over its life. Daily driving across rocky terrain is likely to wear out a control arm faster than special occasion drives down the well-maintained boulevard.
Whichever way your driving habits lean, though, you’ll want to keep your senses alert for any of these symptoms of a bad control arm:
  • Vehicle vibration: if you’re noticing a constant vibration that feels more aggressive than what you’re used to, it could be an indicator of a failing control arm
  • Wandering steering: when the control arm bushings start to fail or become damaged, it’s common for the steering wheel to start pulling to one side or another
  • Wobbling wheels: if it seems like your wheels are wobbling as you drive, bring your vehicle to a mechanic ASAP to have your control arms checked out—wobbling wheels could be a precursor to a wheel falling off
  • Popping or clunking noise: you may notice this when driving over particularly irregular terrain, and it’s one of the earliest signals of a failing control arm
  • Uneven tire tread: uneven tire wear could point to issues with your car’s wheel alignment, often caused by control arm issues
If you suspect there is some failure or malfunction in your vehicle’s control arm assembly, it’s a good idea to visit an auto repair shop. It may be a minor issue now but regularly driving with these compromised car parts could lead to a fully broken control arm and subsequent loss of control of your vehicle.
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Control arm replacement cost

We know heading into an auto repair shop blind to what your potential bill will look like is a scary experience. If you end up in need of a total control arm replacement, be prepared to spend between $500 and $700 on the repair.
The exact amount will depend on your specific vehicle’s make, model, and manufacturing year, but typically, the new control arm itself costs between $400 and $500 and you’ll need to factor in between $150 and $200 extra for labor costs.

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If a control arm breaks while you’re driving, it will get more difficult to steer and maintain control of your vehicle. It’s even possible for a wheel to fall off, which can lead to a collision.
Control arms can break from natural wear and tear over time, or from an extreme impact.
A control arm links a vehicle’s wheel to its frame while still allowing the wheels to move with the shape of the road. It is one of the most important parts of the suspension system.
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