Most cars have two control arms in the front suspension. Often they are called lower control arms. Some cars (e.g. Honda Accord) and many trucks have four control arms, two upper and two lower arms.
What does a front control arm do? It connects the frame or body of a car to the assembly that holds a front wheel. This assembly is called a steering knuckle.
Control arms are connected to the frame or body of a car through flexible rubber bushings, calledcontrol arm bushings. This allows a control arm to swing up and down as front wheels roll over bumps and potholes. The outer end of a control arm has a ball joint. In some cars, a ball joint is bolted to or pressed into the control arm and can be replaced separately. In others, a ball joint comes with a control arm as one piece. Control arms have a very important role holding both front wheels on the road. If a control arm is excessively worn, damaged or bent, the vehicle is NOT SAFE to drive.
Control arm problems
There are a few reasons why a control arm may need to be replaced. A worn-out ball joint that cannot be replaced separately is one of the most common reasons. A ball joint is an extremely important component. If it wears out, the car is unsafe to drive: the front wheel can separate from the lower suspension causing the vehicle to lose control.
In the photo above, the ball joint has separated while driving, although the owner was lucky that it happened at a slow speed. If this had happened on the highway, the outcome could have been much worse.
Worn out or torn control arm bushings is another reason a control arm may need to be replaced. In some cars, control arm bushings can be replaced separately, but it involves more labor and could cost more. For this reason, the whole control arm is usually replaced if the bushings are worn out. The control arm is also the most common part that bends in a collision involving one of the front wheels or after hitting the curb. A bent control arm must be replaced.
Control arm replacement
Replacing a lower or upper control arm can cost from $160 to $390 for one arm. It's not necessary to replace both, left and right arms if one is bad. Often, however, if one arm is worn out, it's reasonable to expect that another control arm will likely need replacement soon. In this case, it's makes more sense to replace control arms on both sides at the same time. After one or both control arms are replaced, the wheel alignment procedure must be performed (another $60-$120).
Do stabilizer bar links need to be replaced whenever a lower control arm is replaced? Stabilizer bar is usually connected to the lower control arms via stabilizer bar links. Sometimes, a nut that holds the stabilizer bar link could be seized and cannot be removed without damaging the link. In this case, your mechanic might recommend replacing the stabilizer bar links as well. In most cars, the links are not very expensive and doesn't require any extra labor when the control arm is replaced.
Can control arm bushings be replaced separately? In some cases, worn out control arm bushings can be replaced separately. However, control arm bushings need to be pressed in with a special tool or press, which takes some time and adds the labor cost.