Control Arm

• A control arm is a metal component of the suspension system, which connects the wheel hub to the frame.
• Its parts include the metal body, bushings, and ball joint.
• They come in unitized, press in, and bolt in designs.
• There are two types of suspension systems that use control arms: double wishbone suspension and Macpherson strut suspension.
• A failing control arm could be due to a faulty ball joint, cracked bushings, or a bent metal arm.
• A replacement costs around $20 to $2,300 for parts alone.

The wheel hub and suspension are attached to the control arm to help with the up-and-down movements of the wheel. This allows the front wheels to change directions whenever you make a turn.

Cars usually have one lower control arm per wheel, while trucks often utilize a two-control arm setup. If your car has only one lower control arm, it’s likely because it has a strut-type suspension. On the other hand, upper and lower arms are typically seen in vehicles with a double-wishbone suspension.

The control arm is a metal connector that links the wheel hub to the frame. It is part of the suspension system, which guides the wheel as it moves up and down.

It is located at the bottom and top parts of your front wheel's spindle and consists of the upper and lower control arm. It allows your front wheels to change direction without any resistance.

The inner end of the control arm attaches to the vehicle’s chassis and serves as the pivot point as the wheel moves. The outer end connects to the steering knuckle. 

Despite its simplicity, the control arm is considered to be an engineering ingenuity due to its function. Each mechanism is made up of three parts.

Metal Arm

The metal arm is the body of the control arm. Back in the day, the the A-shaped design was the most common. Today, modern control arms come in unconventional designs as products of extensive research and developments, especially in performance vehicles.

Bushings

These can be found on the inner end of the control arm. They prevent metal-to-metal contact as the arm pivots in conjunction with the wheel. The bushings also keep the cabin from vibrations while driving on uneven surfaces.

Ball Joint

The ball joint is found on the outer end of the control arm, which connects to the steering knuckle. Located below the coil spring, this part makes wheel turning possible.

Unitized

This arm has a built-in bolt joint and comes in a single assembly. So, when the arm or ball wears out, the whole unit is replaced.

Press In

This kind comes with a bigger ball joint and is used in a wide range of applications. It is often fitted in heavy vehicles like trucks, vans, and SUVs.

Bolt In

This design comes with a stamped strut-type arm body and is used in MacPherson strut suspensions.

There are two types of suspension systems that use control arms.

The double-wishbone suspension uses A-shaped control arms, while the MacPherson strut suspension uses only one control arm. Instead of an upper arm, a vertical telescopic strut linked to a coil spring is used.

Compared to the double-wishbone suspension, the MacPherson strut has more restricted vertical movement. It is less complex and is more affordable.

A double-wishbone suspension produces less noise but is more complicated. It also allows vertical movement.

Small, compact vehicles are typically equipped with Macpherson struts, while double wishbone suspension is more commonly used in larger, more luxurious vehicles, although MBs, BMWs, and Porsches may sometimes be designed with Macpherson strut suspension.

Faulty Ball Joint

A failing ball joint is easy to miss. However, the consequences of this can be catastrophic, as you might lose control of your vehicle after hitting a bump.

The best way to check if your vehicle has a bad ball joint is by having it checked by a licensed mechanic.

Cracked and Damaged Bushings

When control arm bushings start to fall apart, the connection point could become loose and the up-and-down movements of the wheel could be compromised.

Bent Control Arm

The clearest indication of all three is a bent control arm. Control arms are made of steel but that does not guarantee lifetime durability. Keep in mind that your car’s overall weight is distributed to the suspension system. Hitting bumps or being involved in a frontal collision can bend the steel. A vehicle with one or two bent control arm poses a high risk, even a threat, on the road so be responsible and have them replaced as soon as possible.

A faulty control arm may cause poor vehicle handling. To restore the performance of your suspension, you’ll have to get rid of the busted arm and put in a new one.

Here are some tips for finding the right replacement:

• Choose a control arm that is compatible with your vehicle's suspension system.
• Search for a high-quality replacement that is manufactured from tough materials and according to industry standards.
• Shop around to find the best prices. The price tag varies depending on the type of suspension system, arm design and features, and rand.

Replacement control arms are priced roughly around $20 to $2,100, while performance replacements are at around $160 to $2,300. The parts are sold individually, in kits, or in sets.

Installing a new control arm in your car requires a bit of patience, skill, and the right tools. 

Needed tools and materials

• Ball joint separator and press
• Ball peen hammer
• Pry bar
• Tire iron or breaker bar
• Torque wrench

Step 1: Prepping the car

Park your car on a solid level surface and apply the parking brake. Using either a tire iron or a breaker bar, loosen the lug nuts on the wheels but do not remove them.

Next, use a floor jack to lift the vehicle and place jack stands underneath both sides of the car. The jack stands should be placed on the pinch welds and the frame, but if your car has a coil spring with SLA suspension, place one of the stands close to the ball joint.

Step 2: Removing the parts

Once the car is secure, remove the lug nuts and the wheels. Take out the cotter pin and pinch bolt from the ball joint and separate the ball joint from the knuckle with a ball joint separator.

Remove the ball joint nut, steering knuckle and other components still connected to the lower control arm. Once they're removed, detach the control arm mounting bolts and control arm itself.

Step 3: Installing the new parts

Press the ball joint in place on the new control arm with a ball joint press. Slip in the control arm with the attached ball joint to its mounting. Line up and start all the bolts but don't tighten them—this is in case the bolts don't line up correctly on the first try.

Install the steering knuckle, cotter pin, and other components of the control arm back to their respective places.

Step 4: Finishing installation

Reinstall the front wheels and lug nuts and lower the car to the ground. Once the vehicle is at a normal riding height, torque the lug nuts and control arm mounting bolts according to their proper torque.