AuZZZie

G'day lads..

I just picked up a '08 C300 with low KM in great condition but have one small problem/annoyance.

I noticed an almost air leak like sound. Kind of like what you would hear with air in the coolant system. It is coming from the left side of the engine bay which I believe is where the brake master cylinder is.
If you step on the brakes, sound is gone. Soon as you release the brakes sound is back.

Looking at the maintenance records the brakes were bled only 3 months before I bought it, but what are peoples opinions? Do it again? Brake pedal feel doesn't seem off so I'm not sure if that is it.

Hoping to get some ideas before I look into it further.

qaz393

hey,.

i just noticed the same problem with my car. I Think its a leaking airhose or leaking master cylinder. I am going to take it to the dealer in a month because that is when my service is due.

AuZZZie

I've read quite a few people having a leaking booster/maserter cylinder/boot with Mercedes. I can't say I've ever had a brake related leak in a single other vehicle I've owned.

I find it a bit odd.

qaz393

yup. i just noticed the hissing sound this morning. when i press the pedal a bit. the noise dissappear and when i release fully its back. I think its still safe to drive since its not leaking when i depress the pedal. The only thing that nmight be a problem is the leak sucking in dust causing excessive wear. oh well, im going to bring it in dealer in a month.

pope2001

I have an 2008 w204 30k miles and have the same hissing noise, when I press the brake the noise goes away. I am under warranty and plan to eventually take it in. Who has had this issue fixed, and what was it?

AuZZZie

It'll be either the grommet at the firewall, the brake booster, the master cylinder or the vac line from the engine. Most likely the booster from what I've seen so far.

I find it pretty odd how many people have a leaking brake booster on their 2008 W204.

LandSeaAir

I had the issue, took it in, they replaced the brake booster and it was gone.

smehdic300

Was that covered by the warrenty?

LandSeaAir

Yes.

pope2001

thanks, for the feedback on the brake booster, im going to make a an appointment tomorrow.