December 4, 2022

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What is a suspension arm?

A suspension arm, also known as a control arm, is essentially a link that connects the wheel assembly or steering knuckle to the car frame. One end of the suspension arm is attached to a swivelling ball joint, allowing the car wheels to be steered in either direction when driving. On the other end of the arm, there’s a hinge joint which ensures that the wheels maintain contact with the road surface in all conditions. One of the purposes of control arms is therefore to stabilise the vehicle and allow the car chassis and wheels to move in unison while driving or travelling over bumps.

Many suspension systems use two arms for each wheel on an axle: an upper arm and a lower arm. However, MacPherson-type suspension systems only use lower arms in conjunction with the suspension strut. 

Image of car control arm sourced from buycarparts.co.uk

Causes of failure

Control arms are susceptible to different kinds of damage when exposed to extreme temperatures, harsh driving conditions and moisture, or as a result of collisions:

  • Ball joint wear or damage

Symptoms of a bad car suspension arm

  • Unstable or wandering steering

You may notice that the car veers to the left or right without input from the steering wheel. This could be a symptom of a damaged bushing or a damaged ball joint. The issue often becomes more noticeable when driving on uneven surfaces. Don’t forget to check the steering tie rods before replacing the bushings or ball joint.

  • A vibrating steering wheel or car

When the bushings are worn and the components are loose, the steering wheel may start to vibrate excessively as the wheels wobble. 

This is another symptom of a faulty suspension arm, as well as a common sign of poor wheel alignment. Worn or damaged bushings can affect the car’s alignment, causing the tyres to wear unevenly on the inner or outer edges. It is highly advisable to get the car checked and realigned by a professional.

  • Strange noises coming from the suspension

You can sometimes hear a clunking, popping or rattling sound coming from the suspension after braking, going over bumps or potholes, and making sharp turns. It may be possible to treat a corroded car control arm, but it is often necessary to replace the parts.

How often should suspension arms be replaced?

Suspension arm assemblies normally last at least 90,000 – 100,000 miles. However, if you experience any of the symptoms above, it may be time for a replacement. 

How to replace a suspension (control) arm

For detailed instructions, read through your vehicle’s repair manual carefully. There are also useful step-by-step tutorials for popular car models. The steps to this general repair procedure are outlined below.

General replacement guide

  1. First you will need to raise the car using either a car lift or jack and jack stands. Remember to remove the wheel
  2. If the control arm screws and nuts look a little rusty, treat them with a suitable rust remover. This will make them easier to remove.
  3. Loosen the control arm fasteners to disconnect the component from the chassis.
  4. Disconnect the tie rod with the ball joint using a special tool.
  5. Remove the old control arm
  6. Install the new part in reverse order. Use new fasteners to secure the arm
  7. Tighten the nuts and bolts to the recommended torque specified in the repair manual
  8. Once you have finished installing the component, you can reattach the wheel and lower the vehicle