Control Arm Buyer's Guide
- A control arm is a metal component that’s part of the suspension system that connects the wheel hub to the frame.
- The parts of a control arm include the metal body, bushings, and the ball joint.
- The types of control arm design include unitized, press in, and bolt in.
- 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.
- Consider your vehicle's suspension system type as well as the price and quality of your replacement when shopping for a control arm.
- It costs around $20 to $2,300.
- Installing a control arm on your own is easy is you have the right tools and know-how.
To help with the up and down movements of the wheel, car manufacturers attached the wheel hub and suspension upright to a control arm. The control arm allows the front wheels to change directions whenever you make a turn. Hence, this suspension part really is something you can't drive properly without.
The layout of the wheel assembly depends on what kind of car you are driving. Front-wheel cars usually feature one lower control arm per wheel, while trucks often utilize a two-control arm setup. If your car has one lower control arm, it’s likely because it has a strut-type suspension, as opposed to having an upper and lower arm which indicates a double-wishbone suspension.
What is a control arm and why is it a key suspension component?
The control arm is a metal connector that links the wheel hub to the frame. This crucial component is part of the car’s suspension system that guides the wheel as it moves upward and downward.
It is located at the bottom and top parts of your front wheel's spindle and consists of the upper control arm and lower control arm. They permit your car's 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 of the arm whenever the wheel moves up and down. The outer end, on the other hand, connects to the steering knuckle. Without the control arm, there’s nothing to support the wheel movement and suspension system.
Parts of a control arm
There’s nothing complex about the structure of the control arm. It features a simple mechanism that consists of three parts. Yet, despite its architectural simplicity, control arms are considered to be an engineering ingenuity due to its function. That said, here are the parts comprising a control arm.
The metal arm is both the skeleton and body of a control arm. It comes in varying shapes and designs but the most common of all back in the days is the A-shaped design, which made some people call it the A-arm. Modern control arms nowadays exhibit unconventional designs as products of extensive research and developments, especially in performance vehicles.
On the inner end of the control arm, you’ll find a set of rubber bushings. These bushings are there to prevent metal-to-metal rubbing as the arm pivots in conjunction with the wheel. The bushings also keep the cabin from vibrations caused by uneven road surfaces.
The ball joint is found on the outer end of the control arm, which connects to the steering knuckle. Located below the coil sprin, the ball joint makes wheel turning possible.
Types of control arm design
This arm has a built-in bolt joint. It comes in a single unit and not a separate piece. So when the arm or ball wears out, the whole unit is replaced.
This kind is used in wide-range applications, though this seems more fitting for heavier vehicles such as trucks, vans, and SUVs. This arm design uses a bigger ball joint.
This design is used in Macpherson strut suspension. It comes with a stamped strut-type arm body.
Double wishbone suspension vs. macpherson strut suspension
There are basically two types of suspension systems that use control arms.
The double wishbone suspension uses A-shaped control arms. Meanwhile, the macpherson strut suspension uses only one control arm—instead of an upper arm, a vertical telescopic strut that’s linked to a coil spring is used.
Compared to the double wishbone suspension, the Macpherson strut has a more restricted vertical movement. It is less complex, and in terms of cost, it’s less expensive.
Double wishbone suspension, on the other hand, is quieter but also more complicated. It 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.
Indications of faulty control arms
There are three main reasons why you need to replace your car’s control arm. If you notice strange movements on your wheel, act responsibly by consulting your mechanic. If he or she finds out that the issue is caused by a damage control arm, the only best thing to do is have them replaced because damaged control arms make your vehicle unsafe to drive.
Faulty ball joint
The ball joint is integrated to the control arm and typically comes with it as default. A failing ball joint is easy to miss; your car might have it without you even noticing. However, the consequences of this can be catastrophic, as your car might end up losing control after hitting a bump.
One quick method of testing the ball joints is to hold one with your fingers and wiggle it about. If it offers little to zero resistance, then you definitely need a control arm kit. Otherwise, your car's steering is going to get even worse. The best way of detecting a defect on the ball joint is through a thorough check-up by an experienced mechanic.
Cracked and damaged bushings
The bushings play a vital part in the pivoting movement of the control arm, as it prevents the metal connection points of the frame and the arm from rubbing on one another. It also negates the noise from metal-to-metal contact, as much as it absorbs vibration on rough roads. When control arm bushings start to fall apart, the connection point could become loose and the up and down movements of the wheel will be compromised.
Bending on the metal as a result of impact hits
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.
What to consider when buying a control arm
A faulty suspension arm may result in loss of precision and poor handling. To bring back the good performance of your suspension, you’ll have to get rid of the busted arm and put in a new one. When in the market for a new control arm, you have to:
- Know the type of suspension system used in your vehicle and the suspension arm design that will match the specs and requirements of your vehicle.
- Search for a high-quality replacement. It has to be made from high-grade materials and has to be tested to meet industry standards.
- Shop around and compare for the best prices. The price range varies according to the type of suspension system, arm design and features, brand, and seller.
How much is a control arm?
The price depends on what kind of control arm replacement you are after. There are two kinds of replacement control arms, which are OE and performance replacements. OE replacement parts are the ones designed to readily fit your car, while performance replacement control arms are meant to offer additional rigidity and are meant for more intense driving. OE replacement control arms are priced roughly around $20 to $2,100, while performance replacements are at around $160 to $2,300. The parts come as an individual piece, in kits, and sets.
How to install a control arm
Whether you're replacing a faulty control arm or just switching to a high-end performance arm, installing a new control arm in your car requires a bit of patience, skill, and the right tools. In this installation guide, we'll show you how to properly install a control arm on your car.
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. Preferably 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.