t0404

Hi Guys, I've just got a CPO 2010 C300 at 30,000 miles. Not sure if this has always been the case, but recently I've been noticing hissing sound coming out of the brake. Perhaps, I just never noticed it before. The sound goes away when I step on the brake, but comes back when my foot is off the brake.

I read a few threads here as well, and some people said it's because of the air brake booster. I brought my car to the dealership to see if that's the case. The service guy there said it was normal, and he even brought me another 2010 C300 to show that the sound is in fact normal.

So here I am reaching out to you to see if you've noticed anything similar in your C300's. The sound has been really annoying, and I just can't seem to get used to this "normal" thing.

Thanks a bunch.

LandSeaAir

The same thing happened in my 2008 c300, they replaced the brake booster under warranty and it went away.

I'd try another dealer.

t0404

Thanks, man. Brought the car back to the dealer today and asked to talk to the service manager. A different technician looked at my car today and agreed that there was a problem with the brake booster. Took a loaner GLK out for the day and enjoyed the free 150 miles.