Knocking Noise Under Your Car When Driving? How to Diagnose Bad Sway Bar Links

Do you hear a knocking sound on your car while driving that’s similar to the one in this video? Find out how to diagnose and fix bad sway bar links with these tips from our expert mechanics.

What Is Causing a Knocking Sound from Under My Car While Driving?

1A Auto mechanic under a car and holding a bad sway bar link that made a knocking noise

If you hear a knocking sound under your car while driving, you’ll want to inspect the sway bar links. Sway bar links are known to cause this kind of sound when they’re worn out and have too much play.

What Is a Sway Bar Link?

4 Different types of sway bar links
Different types of sway bar links

The sway bar is a part of your car’s suspension. It has a joint that pivots and links to the sway bar. The sway bar stops the vehicle from swaying. Not every vehicle has sway bar links—some have torsion bars, but these parts keep the vehicle stable and from shifting weight and rolling over when it needs to swerve.

Sway bar links come in many shapes and sizes depending on the vehicle. They may or may not have components like bushings and washers. They attach to a joint inside so they can sway with the vehicle.

The sway bar link can disconnect and knock against parts like the axle or control arm. It could also hit against the tire or fall back and break the brake hose off. The owner of the vehicle featured in this article’s video decided to saw off the top of the sway bar link, but we don’t recommend this.

It’s safe to wire-tie the sway bar link back into place if it disconnects, but it can come undone again from the car swaying.

How to Diagnose a Sway Bar Link

Look for these symptoms to tell if you have a bad sway bar link.

More on diagnosing a bad sway bar link

Symptoms of a Bad Sway Bar Link

Knocking Sound

When the joint on the sway bar link is worn and loose, it will make a loud knocking sound that echoes into the cabin. The joints on sway bar links can form flat spots, move too freely, and knock from use over time. The grease can also wear out from contaminants and use.

Torn Boot

If the rubber boot on the sway bar link tears, grease can leak and contaminants can enter, wearing the sway bar link out quickly.

Broken Components or Rust

Like in the example featured in this article’s video, the sway bar link can rust from debris like road salt and if it’s too worn can break off from the sway bar.

How to Replace a Sway Bar Link

Watch the steps in this how-to video to learn how easy it is to replace a sway bar link yourself.

Shop Quality Auto Parts

Fix a bad sway bar link yourself with quality auto parts at 1aauto.com
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Knocking Under the Car When Driving? Diagnose Bad Sway Bar Links - 1A Auto
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Knocking Under the Car When Driving? Diagnose Bad Sway Bar Links - 1A Auto
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If you hear a knocking sound under your car, it's time to check the sway bar links. Learn how to diagnose bad sway bar links with the expert tips from the 1A Auto mechanics in this article and video
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1A Auto
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