Mercedes-Benz S420 Control Arm Replacement Cost

While there is no prescribed frequency for replacement of a control arm, the bushings may wear out and need to be replaced as a vehicle approaches 100k miles. Driving aggressively or over rough roads can decrease the lifespan of the control arm bushings.

A technician may diagnose a worn lower control arm during a test drive of the vehicle. The condition may also present itself during a bounce test, where the technician will press down firmly on one corner of the vehicle to bounce the suspension and pivot the control arms. A damaged or bent control arm may show up during a four wheel suspension alignment since the control arm determines the position and angle of the wheel.

A technician will replace a lower control arm by first lifting and supporting the vehicle in the air on a hoist and removing the wheel and tire. A lower control arm must be disconnected from the lower ball joint (attached to the steering knuckle) and from the vehicle frame or body. An upper control arm is disconnected from the strut tower on the body and from the top of the steering knuckle. Some control arms come with bushings permanently installed in them, while others require the bushings to be installed. It is common to replace related components - ball joints, tie rod ends, sway bar links - at the same time that a control arm is replaced.

Replacement of a control arm is generally an intermediate DIY repair. On some vehicles, the control arms come with the bushings already installed. On other vehicles, the bushings need to be pressed into their housings on the control arm before installation into the vehicle. In this case, the repair will be more difficult. Also, this repair requires that the vehicle be safely lifted and supported with a jack and jack stands. Failure to do so in a safe manner can result in serious injury or death.