5

I have a 2002 BMW E39, the car gives a knocking noise when braking, which can be felt and heard from the front. Outside it is much louder than inside.

Could this be caused by a rotten brake dust shield?

Thanks!

  • 1
    Noise should be more or less constant if it's the shield making contact with the disc – I have no idea what I'm doing May 10 '16 at 8:58
  • One knock or consistent knocking when brakes are applied? – Moab May 10 '16 at 14:00
7

A knocking noise when braking (or during less noticeable maneuvers) can be attributed to worn front suspension parts - especially control arm bushings.

The image below is from some random heavily worn lower control arm bushings. As you can see, the rubber wears out and the connector in the middle is free to wiggle and knock around. Using your brakes puts a lot of stress on these bushings so it's more likely to be heard at that time.

Other symptoms, which may or may not be present, are a noisy clattering on a bumpy road, odd steering feel/behavior at low speeds, and pulling to one side when braking. Also, your alignment would normally be out of wack so tire wear may be uneven.

If you can get you car up on jackstands, a worn bushing is sometimes easy to see (depends on the car).

control arm bushing

Click for larger image

1

It is unlikely to be caused by a rotten brake dust shield, if the knocking is repetitive with a frequency that alters with speed, that would suggest that it's source is something that is rotating. Perhaps a badly warped brake disk?

  • Every brake disc and brake pad has bern replaced 1 week ago so that is not case. – Balázs Vincze May 10 '16 at 12:15
  • Are the wheel nuts tight? Can you feel it through the steering and/or the brake pedal? – tallpaul May 10 '16 at 12:18
  • Yes, I can feel it through the steering, the brake pedal I am not sure... The lug nuts are tight as well! – Balázs Vincze May 10 '16 at 12:47

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