A vital suspension system linkage component in many production vehicles, control arms connect the chassis to the front wheels on many vehicles.
Some vehicles only have one control arm per wheel, while others have two or none. Control arms are typically stronger than linkage designs used in race cars, but have more unsprung mass.
Control Arm Bushings
In order to prevent binding, excessive wear, unpleasant noise, and other undesireable qualities, the points where the control arm pivots against the vehicle frame are typically designed with a thick rubber/silicone bushing. These bushings need to be greased periodically to flush out dirt and any worn off material.
Ball Joint
The point where the control arm attaches to the bracket which holds the wheel hub needs to be able to move into many different angles, since it has to move with the steering and suspension at the same time. As the name suggests, the joint is a sphere to allow the necessary movement, and a post allows the joint to be bolted to the hub bracket. Ball joints need to be greased as well, and typically encounter more debris, movement, and are in a harsher environment than the control arm bushings. A ball joint is also a type of ball-in-socket joint, which can be found in other components on a vehicle.