Symptoms
- Knocking sound from the front of the car over bumps
- Sometimes accompanied by a clunk during braking or acceleration
- Noise seems to come from one side more than the other
Likely causes
- CommonWorn ball jointBall joints allow suspension movement and steering; once worn, they develop play that knocks.
- CommonWorn strut or strut mountA failing strut or its mounting hardware can knock over bumps.
- PossibleWorn control arm bushingBushings that have deteriorated let the control arm shift and knock.
What to do
- Note when the knock happens: over bumps, during braking, during acceleration, or turning.
- Have a mechanic put the car on a lift and pry on suspension components (ball joints, control arms, sway bar links) to find play.
- Check strut mounts for looseness by having a helper turn the wheel while you feel near the top of the strut tower.
- Replace the specific worn component identified.
- Have the alignment checked after any suspension repair, since replacing these parts can change alignment slightly.
Tools and parts
Ball jointSearch: “ball joint for [your car model]”
Control arm assemblySearch: “control arm for [your car model]”
When to call a pro
This diagnosis is best done on a lift with someone physically prying on components, which is hard to replicate safely at home.
Safety
Use caution
A severely worn ball joint can fail suddenly and cause loss of steering control; have persistent knocking diagnosed promptly.