What are Suspension Control Arms? What do they do? How do they work?
What are control arms?
Control arms are the core of your front suspension system. In simple terms, control arms are the link that connects your front wheels to your car. One end connects to the wheel assembly and the other end connects to the framework of your car.
The upper control arm connects to the uppermost area of the front wheel and the lower control arm connects to the lower most area of the front wheel, with both arms then attaching to the frame of the car. If you have independent rear suspension, the design is similar.
What are the types of control arm suspensions?
The most common types of control arm suspensions are:
- Control arm type suspension
- Strut type suspension
Strut type designs have a lower control arm but no upper control arm. In strut designs, the strut becomes the upper control arm and is sometimes connected directly to the spindle or the lower control arm.
How do control arms work?
Each control arm is connected to the vehicle frame with two control arm bushings. These bushings allow the control arms to move up and down.
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 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.
WHAT DOES A CONTROL ARM DO?
To keep it simple, the control arm is a link that connects the frame of the car to the wheel hub assembly or steering knuckle. Control arms can come in many different shapes in sizes, upper Control arms are often call “A” arms as they have a shape vaguely like a capital letter A. The control arm(s) move up and down with the spring when a car hits a bump or other road irregularity. This allows the tires to maintain contact with the road and, thus, control. The control arm is part of the suspension system that helps your car remain in full contact with the road at all times, that’s giving you necessary control.
In most control arms, the two lower parts of the “A” are attached to the frame via control arm bushings, which are rubber pivot-points. The top of the “A” is attached to the steering knuckle by way of a ball joint. In older vehicles, this ball joint is serviceable on its own, without the need to remove or replace the control arm. On most newer vehicles, the ball joint is incorporated into the design of the control arm, hence, the entire arm must be replaced. Vehicles can have a different numbers of control arms. Some have as few as just one lower control arm, many vehicles an upper and a lower, and some even have more elaborate, multi-link arm set-ups.
When a control arm fails, multiple things can happen. Most failures occur from the ball joint failing. Complete ball joint failure can cause a steering knuckle disconnection and loss of control of the vehicle. Control arm bushings can also wear and fail, creating clunking, wandering steering, and loss of control. Before your control arm gets to this point, be on the lookout for these signs.
BAD CONTROL ARM SYMPTOMS
1. POPPING NOISE
One of the earliest signs of a failing control arm is hearing a popping noise when you drive over road irregularities. You may also hear a popping noise when you speed up or reduce the speed of your vehicle, but normally going over bumps at slower speeds, like speed bumps is an indicator of a ball joint that is popping, or possible worn bushings.
2. STEERING IS UNSTABLE
Another symptom that can indicate control arm problems is unstable steering. This is very common in failing bushings, where the alignment of the steering wanders, causes the car to veer either to the left or the right when the driver runs over a bump in the road. This issue becomes more apparent if the car is driving on uneven surfaces or unstable terrain. This symptom may also indicate that your idler arm or steering tie rods are in bad shape, so when inspecting, make sure to check the steering components.
Consistent vibration throughout the vehicle could also be an indicator that the control arm may be starting to fail, but not exclusive to this. Given that the control arm absorbs a lot of the energy and is the link between the suspension and the frame, other issues like unbalanced tires, or failing steering components will only be worse if your control arms also have weak components.
3. UNEVEN TIRE WEAR
Uneven tire wear is also a potential sign of a failing control arm, as this is an indicator of alignment issues. As control arm bushings wear, this can force the vehicle out of alignment, causing wear on the outer or inner edges of the tire. While sometimes this is just an indicator that a proper alignment is needed, it can also be caused because of worn bushings. Any alignment shop will be able to properly diagnose this.
WHAT TO DO ABOUT CONTROL ARM PROBLEMS
If you are noticing any of the above symptoms, get your car to a shop for a full suspension check. If you are an avid DIYer, get your car up on jack stands and thoroughly check out the control arms and front steering for any issues. In the event that your control arm or another suspension link or arm fails while you are driving, you want to try to slow the car down and get it off the road if you can. Remember that in the event of a complete failure of the control arm that you may be unable to steer the car.
Remember that you need to realign your vehicle after you replace anything having to do with the control arm, suspension, or steering.
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