Whizzing sound when braking

[blondebier]

Hi Guys,

I've got a bit of a weird sound when I brake in my W201.

When I slow down almost to a stop and apply the brake hard I hear a "whizzing" sound that appears to come from behind the dashboard.

It doesn't happen all the time and is only audible when the car has been driven for a little while. I.e. It doesn't happen when cold.

Any ideas what it could be? Braking doesn't seem to be affected. It's just annoying.

Cheers,

Blondebier

 

[camerafodder]

Maybe a fan moving in its housing slightly under G force.

 

[blondebier]

Maybe... It's really hard to tell.

I wandered if it might be the servo that assists the braking...

I need to look into it a bit more. Does anyone have a diagram of the braking system on a W201? (Mines a late 190D 2.5 if that makes any difference.)

The more I think about it the servo is on the drivers side on the bulk head near the top... I reckon it's probably this.

How long have I got before it needs replacing? Are my brakes likely to get worse/fail quickly?

 

[kwakdonut]

Possible air leak from the servo? Check the pipework to it

 

[blondebier]

The only pipe I can see connecting to it is the cream one running over the top round the front of the engine bay.

I assume this is the vacuum pipe?

It looks fine and there aren't any cracks in it.

 

[kwakdonut]

That will be the one. Have you checked the connections at both ends as well as its general condition?

Try checking it with the engine running too. If you can discount the hose then you can start to look elsewhere, such as the servo itself

 

[blondebier]

Thanks Kwakdonut. I'll check it with the engine running later.

Is there an easy way to test the servo? Are there any symptoms I should look out for?

 

[kwakdonut]

You're welcome.

If you have a helper, that would be useful. Run the engine and press the brake pedal a few times while you listen and feel for any leaks etc. The problem you have may then become a little more obvious.

 

[blondebier]

Ok, I've checked for leaks.

I couldn't see anything that would cause concern. It all appeared to be sound.

It is intermittent as well which makes it really irritating and hard to diagnose.