mak29khan

Hello Everyone,

I currently drive a 2016 C 300 with roughly 70kms on it. A few months ago, I noticed my brake pedal was making a hissing sound when let off (see attached video).

I’ve taken the car to the dealership many times, around 3-4 times. But, they deem the hissing sound to be “operational” and can’t find any “mechanical” issues with the brake booster. I’ve gotten a second opinion from a different mechanic, who advised it’s definitely the brake booster. Has anyone else come across a similar situation? Where the dealership deems the part to be “operational” and therefore doesn’t see the need to change/replace the part.

Update: Can’t seem to upload the video from my phone. Will post it tonight.

Thanks!

GreekUPS

Dealership just changed mine back in October. Hissing sound way more prevalent than in cold weather.

GringoBling

My 2015 C400 does the exact same thing, dealership also tested it and its operationally sufficient. So it just does that sometimes.

mak29khan

Did you have to fight for a replacement? Or was it the dealership's own conclusion? Thanks.

mak29khan

I just uploaded my video. Let me know if yours is similar.

I just find it odd that they consider a "hissing" sound from the brake pedal normal.

DylanM

It's "normal" in the sense that it is widespread, but it is a real issue that affects a large base of vehicles - the underlying problem is a leaking brake booster.

After taking the car in numerous times for this, and getting some great advice from others who have fixed this in the past, I can confirm that finally getting the brake booster replaced with a new superseded part completely fixed the issue (even at very low ambient temperatures).

One additional thing this corrected is a vacuum leak in the system which can cause a loss of power particularly when accelerating from a stop - would definitely recommend getting it replaced just for this.

bzammitt

Do you have the new part number that yours was replaced with? Mine has done this since I owned it and I would love to replace it myself (car isn't under warranty)

DylanM

Don't unfortunately - that's what the SA noted when I picked up the car after the fix.

GreekUPS

I’ll take a look at my service records to see if the part number is there.

GreekUPS

I drive a ‘15 C300 4Matic.