W126 Front Knocking Sound When Braking ...
 

There is this sound that has recently developed and the guys at the garage hasn't a clue what it is. Everytime the brakes are applied, there seem to be a knocking sound coming from the front. The sound is most apparent when braking down from 40 km.

With the brakes squeaking and now this knocking, makes me think that this car has some hidden and unappreciated talent.

What should I be looking for?

:confused:

Is it a knock, clunk, or a creaking sound?
 

Greetings,

This sound you hear, is it coming from one wheel in particular and exactly what does the sound imitate? Couldn't be a moving brake pad moving in it's holder, could it? It could also be a strut rod mount or wheel end mount moving as the pressure increases.

Charles

Is it just one or two knocks when coming to the stop? Or does it knock, knock, knock all the way until stopped?

Its only a knock when the brakes are applied, and then you'd feel the pressure of brakes being applied. Its irritates.

I asked the MB dealer and he thinks it could be the case of either:
1. a dirty ABS sensor, which needs to be cleaned; or
2. faulty brake relay.

I notice this morning that the knock was absent (a wet morning). So I conclude that it comes up only when its hot.

How will the strut rod mount or wheel end mount create this knock?

Thanks for the comments.

:)

Greetings,

Forward vehicle motion forces the chassis weight to shift and causes movement of the strut rod into a loose wheel end mount causing a knocking sound or the guide rod on the opposite end shifts into the defective mount causing a metal to metal contact.


Charles

I am going to print this in hardcopy.

Thank you.
:)

I agree with the strut rod theory. Someone outside the car should be able to see the tire jerk toward the rear at the moment you hit the brake pedal.

The following links will give your more info:

http://www.peachparts.com/shopforum/diesel-discussion/8458-300sd-suspension-noise.html?highlight=Caster

http://www.peachparts.com/shopforum/tech-help/12712-heres-question.html?highlight=Caster

David