A control arm is a suspension component, usually made of heavy gauge steel or aluminium, that links the steering knuckle in the front — or axle carrier in the rear — to the vehicle’s frame. Many vehicles have upper and lower control arms. The inboard link(s) of the arm securely bolt to the frame of the vehicle through rubber bushings, while the outboard link of the control arm connects to the steering knuckle through a ball joint; all of which allow the control of the up and down movement of the steering knuckle or axle carrier. This minimises the transmission of shock and vibration to the vehicle’s body.
The structural portion of the control arm can last the vehicle’s life — except for cases of corrosion or crash damage. However, the rubber bushings and the ball joint in a control arm have a limited life. A mechanic should investigate if you notice:
The vehicle is raised and supported on steel jack stands, and the wheel and tire assembly is removed. Stabiliser bar links are detached from the control arm, if applicable. ABS wiring to the wheel speed sensor, if routed along the arm, is disconnected. Control arm mounting bolts are detached from the frame and from the axle carrier if the control arm is in the rear. For front control arms connected to the steering knuckle via a ball joint, the nut is removed from the ball joint stud, and the stud is pushed through the steering knuckle to free the arm. The arm is lowered from the vehicle and examined by the mechanic to confirm that the noise, or other problem, actually originated from a defect in the arm. The new arm is installed using new mounting bolts if required by the service manual. In many cases, the mechanic must tighten the fasteners with the vehicle weight on the suspension to ensure the bushings are in a neutral or resting position. The vehicle is lowered and road tested to confirm the problem is resolved. Replacing a control arm will change the vehicle alignment settings and the mechanic will refer you to a professional alignment shop to have the vehicle alignment set to factory specifications.
No. If the car wanders on the road, pulls to one side, or noise from the suspension is loud, you need to schedule repair right away. Should the problem be limited to low noise levels, such as clunking or squeaking, continued use of the car is reasonable until you can schedule a repair. Should the control arms be damaged due to a collision, it would be unsafe to drive the vehicle until it is repaired.