What Does the Control Arm Do?

Control arms, as a component of the vehicle’s suspension system, often do not receive the attention they deserve and may even become one of the most easily overlooked parts. People tend to associate the performance of the suspension with the shock absorber assembly. However, control arms serve a similar function as well.


Even though the control arm may appear to be a simple component, its role may not be as apparent as the shock absorber assembly at first glance. However, when the control arm malfunctions, it not only affects the driving experience but can also pose a serious threat to driving safety. This article will delve into the symptoms of bad control arms, their causes, and effective methods of preventing and addressing control arm damage, aiming to assist everyone in maintaining their vehicles in optimal condition.

Basics and Structure of the Control Arm

The terms “Control Arm,” “Lower Arm,” “Upper Arm,” “Link,” “A-Arm,” “Suspension Link,” and “Suspension Arm” are often used by technicians or individuals discussing control arms. They all refer to components connected to the vehicle body. For a more precise and unambiguous terminology, the appropriate term to use is “Suspension link.”

Generally speaking, the main structure of a control arm includes a metal body, usually made of steel or aluminum alloy, which determines the position of the wheel, while the other end is connected to the car body or subframe. As for rigid axles, they are generally less associated with control arms, therefore, they are not discussed in this article.

(Read more: Aluminum Control Arms: What are the Features and Benefits?)

The apex of the control arm is secured to the wheel carrier (steering knuckle or hub) through a ball joint or similar device. This design allows the control arm to move up and down, as well as turn, while restricting the forward, backward, and lateral movements of the wheel, ensuring that the wheel remains in the correct position at all times.”

What is the Function of the Control Arm?


During driving, the shock absorber assembly is responsible for absorbing vibrations from the road surface, while the impact forces are borne by the control arms. When a vehicle passes over a pothole or faces the bump, the control arms must be able to handle the dynamic of the car body’s instantaneous sinking. On the other hand, as the vehicle traverses any uneven road surface, the wheels also experience an impact force opposite to the direction of the vehicle’s travel (as if hitting something). Ensuring that the tires do not undergo any uncontrollable displacement is fundamental, and engineers aim to minimize any unpredictable tire movement to ensure ride comfort—this is another function performed by the control arms.

Common Symptoms of a Bad Control Arm

How can you identify bad control arm symptoms? Catching early symptoms of a bad control arm is crucial for a smooth and safe drive. In this section, we delve into six common symptoms that signal issues with your vehicle’s control arm. Stay ahead in vehicle maintenance and ensure a comfortable, secure driving experience by learning these key indicators.

Noise:

When the bushing or ball joint of the control arm wears or becomes damaged, you may hear some knocking sounds during steering. Since the sound is transmitted from the chassis to the bottom of the car, we can determine if it is a control arm issue based on the location of the noise. However, when traversing uneven road surfaces, the noise could also be generated by the shock absorbers.
(Read more: 6 Symptoms of a Bad Ball Joint and How to Test It?)

Wheel Alignment:

When the control arm itself is damaged, typically bent or deformed, it can result in the tires being unable to maintain proper alignment. A common situation is when a vehicle has just undergone a wheel alignment, but shortly afterward, the driver feels that the vehicle is not going straight again. The timing of alignment failure can vary depending on the severity of the bend and the material of the control arm.
The worst-case is; when the vehicle is handed over to a tire alignment shop, and the technician discovers the alignment failure during the road test after completing the alignment, but without knowing the cause. They re-alignment it, making the value show on the instrument “normal,” and then delivering the vehicle to the customer.

Bad Handling:

As mentioned above, when alignment fails, it means that the control arms cannot fully control the position of the tires. Consequently, the chassis angles considered by engineers during design become failure, leading to a significant decrease in vehicle handling.

Poor Driving Stability:

Deformed control arms can result in the inability to maximize the contact area between the tires and the road surface, leading to decreased stability, especially at high speeds.

Vibration:

Since the structure inside the bushing is composed of rubber responsible for absorbing vibrations, deterioration or hardening of the rubber, a natural material, is inevitable over time. This can result in the control arms being unable to effectively absorb vibrations, making the driver feel a “gap” in the chassis. Additionally, damaged control arms may contribute to resonance within the vehicle, leading to premature wear on the body or other components.

Unresponsive Steering:

The ball joint of the control arm allows for a 360-degree rotation. When the vehicle is turning, a damaged ball joint can result in a “sticky” or hesitant feeling, diminishing the overall driving experience.

The control arm is considered a safety component within the structure of an automobile. Automotive manufacturers prioritize safety in their designs, making it unlikely for the control arm to be used until it is completely damaged or fractured. Repair shops often overlook the condition of the control arm, believing that its impact is not significant. (Sometimes deformation is not visible to the eye.)

The manifestation of control arm damage is often a culmination of small details. Individually, these issues may seem insignificant, but when combined, they can give a sense of discomfort such as “Why does the car feel uncomfortable to drive,” “The chassis feels loose,” “The car seems misaligned,” or “steering wheel not straight.” These sensory differences, indicative of bad control arm symptoms, can be quite apparent. The next time you consider getting a wheel alignment or upgrading the shock absorbers, it might be worthwhile to first check the condition of your vehicle’s control arms!

What Causes Control Arms to Wear Out?

As mentioned, control arm is primarily composed of three main parts: body, bushing, and ball joint. While it’s possible to analyze each of these components separately, the wear and tear on control arms are often interrelated. Therefore, we will provide a unified introduction to the reasons that contribute to the control arm damage.

  1. Uneven Road Surfaces and Impact:
    Excessive bumps on the road can subject the control arms to excessive impacts. This not only causes deformation and bending of the control arm body but may also lead to damage to the ball joint.
  2. Prolonged Overloading:
    While the main weight of the vehicle is supported by the springs, prolonged overloading can still place the control arms frequently in positions not originally designed for. This can result in excessive wear on the ball joint and body of the control arm.
  3. Neglecting Maintenance:
    As a safety component, control arms are not prone to outright failures such as fractures. During maintenance, technicians often only check the smoothness of the bushing and ball joint but frequently overlook deformations in the body of the control arm. This oversight can often lead to difficulties in wheel alignment.
  4. Poor Parking or Driving Conditions:
    1. Deserts and other high-temperature regions
    2. High latitude extreme cold regions
    3.Saline-alkaline or snowy areas
    4. High humidity or coastal areas
    All of the above driving environments can lead to corrosion and erosion of the control arms. To keep the control arms in optimal condition, it is advisable to avoid exposing the vehicle to such environments as much as possible.
  5. High-Speed Passage over Uneven Road Surfaces:
    When a car passes over a pothole at high speed, the control arm experiences a sudden downward force, subjecting the bushing and body to impact. Upon leaving the pothole, the difference in elevation between the road surface and the control arm creates a scenario akin to hitting a wall, causing the metal sleeve and body of the control arm to endure a force opposite to the vehicle’s moving direction. This can result in damage to the connection points of the bushing or deformation of the control arm body.
  6. Poor Design
    Based on experience, the control arms of certain vehicle models may have a shorter lifespan compared to others. In such cases, it raises suspicions that engineers may have overlooked certain factors during the suspension design, resulting in insufficient strength or excessive pressure on the control arms. This leads to a significantly shorter replacement interval for the control arms of that particular model compared to others. (Example: Tesla Model 3, Y)

Solutions for Control Arm Problems

In order to extend the lifespan of the control arms and maintain optimal performance, preventive measures are crucial.

Check the Control Arms During Maintenance:
During vehicle maintenance, pay special attention to the condition of the control arms. Through visual inspection, examine whether the dust covers of the ball joints are cracked or brittle. The ball joint is a relatively precise component with high surface finish requirements. A damaged dust cover may allow foreign particles to enter the ball joint and cause damage. Additionally, check if the rubber portion of the bushing still retains its color and elasticity.

Avoid Driving on Poor Road Conditions:
Crooked surfaces and extreme weather conditions can accelerate the wear and tear of control arms.\

Avoid Aggressive Driving:
Maneuvers such as drifting, rapid acceleration, and hard braking can subject the control arms to excessive stress. If you want to keep the control arms in good condition, it’s advisable to refrain from engaging in these behaviors.

Drive Slowly on Bumpy Roads:
When encountering uneven road surfaces, it’s important to drive at a slow pace.

Wheel Alignment:
Proper wheel alignment is crucial, as incorrect alignment can subject the control arms to prolonged stress. Good alignment can effectively reduce uneven pressure on the control arms.

Consider Replacing Your Control Arms When Needed:
The typical lifespan of control arms is around 8 years or 80,000 miles. Depending on usage, this lifespan may be even shorter. Exceeding 8 years or 80,000 miles indicates significant aging of the control arms, especially the ball joints and bushings. In such cases, it’s advisable to replace your control arms.


Installing new control arms can provide you with a significantly solid and confident chassis feel. Driving your vehicle with the new control arms feels like it’s in the condition it was when it left the factory, without any loose or unstable sensations. This kind of effect is often unexpected before the replacement!
Additionally, in some models, the ball joints and bushings can be individually replaced, allowing you to address specific components before the overall structure undergoes deformation.

Conclusion

Control arms are not only a crucial component in the suspension system but also a key factor in driving safety. While control arms may wear out for various reasons, many common issues can be prevented through proper maintenance and awareness. Regular inspections, maintenance, and avoiding harsh driving conditions can all contribute to protecting your control arms. However, please remember that your needs should still be the top priority. Do not inconvenience yourself by overprotecting chassis components, as this would be putting the cart before the horse! Simply check during your car’s maintenance to see if a replacement is needed.  Instead, during your car’s regular maintenance checks, look out for bad control arm symptoms to determine if a replacement is needed.

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