What is Control Arm? It’s Function, Diagram, Symptoms, Problems, and Replacement Cost.
A control arm, also known as an A-arm, is a hinged suspension link in automotive suspension that governs a wheel’s vertical travel. It helps maintain wheel alignment and tire contact with the road for safety and stability.
The inboard end of a control arm is attached by a single pivot, usually a rubber bushing, which can only control the position of the outboard end in one degree of freedom.
This motion is constrained by a separate link or radius rod. In contrast, wishbone suspensions, triangular with two widely spaced inboard bearings, control two degrees of freedom without requiring additional links.
Honda products from the 1990s feature a double wishbone suspension, featuring both upper and lower control arms working in tandem to locate the wheel.
Control arms are crucial components of a car’s suspension system, connecting the car body to the wheels. They are essential for steering and guiding the wheels, ensuring stability and drivability.
While often overlooked, control arms play a similar and important role in the suspension system. Bad control arms can affect driving experience and safety, requiring maintenance to function optimally.
Control arms are commonly used in the MacPherson strut independent front suspension, providing control to the vehicle’s axis.
These track control arms, perpendicular to the vehicle’s axis, are known as track control arms. The strut is constraint by a diagonal radius rod, which can be attached through a ball joint for longitudinal control.
In modern designs, the radius rod and anti-roll bar are separate, mounted in a sliding bush. Torsion bar suspension, like the Traction Avant, uses control arms to transmit suspension loads to the spring or shock absorber.
A control arm does crucial work in a vehicle, connecting the steering knuckle to the frame and allowing the vehicle to move in unison. It helps achieve coordination between the suspension and steering systems, dampening the ride and enabling driver maneuverability.
The swiveling ball joint serves as the pivot point, allowing the vehicle to be turned in either direction while moving forward or backward. The hinge joint on the control arm’s frame side maintains wheel contact with the ground.
Control arm suspensions are commonly used in vehicles, with two types being strut type and control arm type suspension. Strut type designs have a lower control arm but no upper control arm, while strut designs have the strut becoming the upper control arm and connected to the spindle or lower control arm.
Control arms work by connecting to the vehicle frame with two bushings, allowing them to move up and down. The opposite end of the control arm is attached to a steel spindle, which is bolted to the front wheel.
On non-strut equipped vehicles, the spindle is attached to both upper and lower control arms with a ball joint. A heavy steel coil spring supports the vehicle’s weight and provides cushion against bumps. Adjustable attachment points at the frame ensure perfect alignment.
Frame damage, bushing harm, and ball joint damage are the primary types of damage to a control arm. Frame damage can result from rust, extreme flexing, or breakage from a forceful impact or collision.
Understanding these five common symptoms of bad control arms is essential for maintaining optimal vehicle performance. Over time, wear and tear causes bushing damage, while moving parts in contact can cause ball joint damage or even crack.
A damaged control arm may exhibit symptoms such as vehicle vibration, wandering steering wheel, misalignment, wobbly wheels, unusual grinding noises, fluctuations in braking, and uneven tire tread wear.
To extend the control arm’s lifespan and maintain optimal performance, preventive measures are crucial.
Visually inspecting the control arms for cracked or brittle dust covers on the ball joints and checking the rubber portion of the bushing for color and elasticity. Drive slowly on bumpy roads and ensure proper wheel alignment to reduce uneven pressure on the control arms.
A bad control arm can cause noticeable road noises, unstable or slack steering, tire wear, regular and excessive vibration, and poor handling. Unusual road noises, often resembling popping, clacking, or metallic clicking, are most noticeable when moving over bumps or uneven terrain.
In severe cases, worn control arms can make steering erratic or slow, requiring frequent steering corrections. Excessive vibration, often characterized as a continuous shutter or shudder, can indicate faulty motor mounts.
Poor handling and steering response can be greatly affected by worn control arm bushings, leading to increased body roll and less sensitivity in the steering.
Uneven or irregular tire wear is another clear sign of excessive control arm wear, which can appear all over the tread surface, starting towards the inner or outer surfaces.
The cost of a professional control arm replacement varies depending on the make and model of your car. A new car control arm typically costs $400 to $550, with labor costs for replacing a broken part running $150 to $200.
It is recommended to replace the damaged control arm immediately to avoid future suspension issues.
Factors affecting the cost include the car’s make/model, other parts required, and specialized tools and supplies. Labor costs can vary depending on the location, type of car, and the type of store visited.
For example, a dealership may cost more but offer greater competence and a warranty. The cost of labor depends on factors such as location, type of car, and the level of competence required.
mTherefore, it is essential to consider these factors when determining the cost of a control arm replacement in your car.
The replacement of a car control arm can be a DIY or professional project. The control arm is usually fastened to the component, but some vehicles require forced bushings to be inserted into the mechanism.
The process involves lifting the car, removing the wheel and tire, detaching the lower ball joint from the lower control arm, and then removing the upper control arm from the steering knuckle and strut tower.
A damaged control arm can compromise suspension alignment and damage rubber bushings, which can be harmed by heat and petroleum chemicals.
Regular examination is necessary to ensure the bushings are clean and free of grease or oil. The car must be carefully raised and supported on a hoist and jackstand to replace the control arm.
If a control arm is damaged in a collision, it may cause uneven tire wear and poor handling.
However, driving a car with a broken control arm is still possible, but the part and bushing bracket may come into metal-on-metal contact, potentially leading to further damage.
FAQs
What happens when your control arm goes bad?
Poor handling and increased vibration can negatively impact performance, causing a lack of responsiveness in the steering.
Can I drive my car with a bad control arm?
The steering and suspension may suffer damage, potentially causing further safety risks. Addressing this issue as soon as possible is crucial to prevent costly repairs and maintain the safety of the vehicle.
How do you know if your car needs a control arm?
A clunking noise coming from the front of the vehicle when going over bumps, potholes, or other road hazards can be a sign of a bad control arm.
How much does it cost to replace control arms?
Prices may differ depending on whether a front or rear part needs replacement, depending on the make and model of your car.