What do control arms do

The opposite end of the control arm is attached to a steel spindle. The spindle is what the front wheel is bolted to. On non-strut equipped vehicles, the spindle is attached to both the upper and lower control arms with a ball joint. The ball joint is a steel ball enclosed in a steel socket that allows the spindle and front wheel to rotate left and right and allow the wheels to move up and down following the roads surface.

Sandwiched between the control arm and vehicle frame, positioned in a spring socket, is a heavy steel coil spring that supports the weight of your vehicle and provides a cushion against bumps. To combine the two opposite motions on each end of the control arm, the arms are tied on the frame side to pivot up and down on the control arm bushings.

On the opposite end, the control arm is tied to the spindle and front wheel with upper and lower ball joints. The coil spring supports the weight of the car and dampens the shock of road surfaces. To ensure that the control arms, bushings and ball joints are in perfect alignment, some control arms include adjustable attachment points at the frame. When necessary, a mechanic can align the front end and keep your car driving straight down the road. The lower ball joint is the load-carrying joint in this type of suspension, while the upper ball joint is the follower, with no significant load to support.

It acts only as a second pivot point for steering. Most modern ball joints are sealed and do not require lubrication as they are lubed for life.

Historically, most ball joints had grease fittings called grease zerks and were designed to have lubricant periodically added. The lubricant was usually a very high-viscosity lubricant. Almost all modern vehicles now use sealed ball joints to minimize maintenance requirements.

New technology, especially applied to the internal bearing design and synthetic lubricants along with improved dust boot sealing, has allowed longer ball joint service intervals and better grease retention. While there is no exact lifespan that can be put on sealed ball joints, they can fail as early as 80, miles in modern vehicles, and much sooner depending on the type of driving.

If a ball joint fails completely, the wheel could separate from the steering knuckle which will cause a complete loss of control.

The tire will be at an unintended angle, and the vehicle will come to an abrupt halt. This could damage the wheel and tire, other suspension components, and possibly even other parts of the vehicle. There are a lot of possible signs of a failing ball joint or control arm bushings. Another symptom could be knocking and clunking noises coming from the suspension when going over bumps. The sounds will continuously get louder as the component wears or eventually breaks.

Dry ball joints have dramatically increased friction and can cause the steering to stick or be more difficult. Excessively worn bushings or ball joints can cause wheel shimmy, which may cause vibrations that are felt in the steering wheel. Vibrations may increase during acceleration and smooth out at higher speeds. Another symptom commonly associated with bad or failing control arm components is steering wandering. Excessively worn ball joints, bushings, or a combination of these can cause the vehicle's steering alignment to shift, which may cause the steering to pull to the left or right when traveling down the road.

This will require constant driver correction to steer the vehicle straight. The time for regularly scheduled oil changes is the best time to inspect control arms, bushings, and ball joints.

A quick test drive will allow for a wide range of driving conditions. Cornering left and right, hitting bumps, and cruising on straight and level ground while braking and accelerating are all important to get a feel for any noises or performance issues related to the control arm assemblies. Visually inspect the control arm bushings for cracking, splitting, tears, missing parts, and oil saturation.

When inspecting ball joints, first look to see if the rubber boots holding the grease inside the ball joint are in good shape. If the boot is torn, or just plain gone, chances are the ball joint is in the process of failing. Does your car need a tune-up? Lower control arm in a MacPherson strut layout. Lower and upper control arms in a double wishbone front suspension. Lower control arm of the Ford F pickup truck.

See also: Toyota control arm. Read Next: When should struts and shock absorbers be replaced? When does the tie rod end need to be replaced? When do the ball joints need to be replaced?