W205 Brake pedal hissing when released.

[ZedC]

Hi all,

Im new to the forum but not new to Mercedes ownership.

2 months ago we purchased a 2016 approved used c class convertible and very recently having a number of issues with the main concern being the brakes.

When you brake and release the pedal it makes a hissing noise, returns back slower than expected and there is then a delay in acceleration.

After having done some research am i right in thinking there is an issue with the brake servo?

My car is with the dealers at the moment and im being told the brakes are fine and feel like im being fobbed off.

The 2019 courtesy c class i have doesnt have any of these symptoms and when i questioned this the response i got was its a newer car.

I purchased approved used so issues like this would be covered.

Anyone else had this problem and how did you get it sorted?

 

[Teego]

Never had this problem. Thing is you bought an approved car. If there wasn't a problem with the brakes why would you bother to take it back? Their point about a newer car being different is absolute bullshit. My 2006 CLS55 has brakes as strong as when it left the factory.
Ask for the Approved Inspection check sheet. If it's an issue get another PDI done and get any issues fixed.

 

[ioweddie]

warranty

 

[RonFleet]

My 2016 C Class' brakes don't do that. There is a fault, IMHO.

 

[Smiley]

That is most likely a symptom of a leaking brake servo. The hissing noise is the vacuum escaping. The place where it is leaking needs to be identified and it will probably need to have the servo replaced. Not common but it does happen. It will not be cheap and can be a PITA job.
If it were me and I was being fobbed off over this I would make a short video of the sound and then write to the dealer principal suggesting to him/her that this is a serious safety issue which needs to be fixed.

 

[clk208]

How long ago did you buy the car?

If I remember correctly the dealer rather than the warranty company has to foot the bill within the first few weeks of any problems As they should have been picked up on the inspection.

From the customer perspective you have a 12 month approved used warranty, it’s just who is footing the bill. I have found the less reluctant to fix major problems like this early after purchase for this reason

 

[ioweddie]

Take it to a different dealer

 

[ZedC]

Thanks for all the replies. We purchased the car at the end of November 2019 and within the first few weeks i have raised several issues of which the brakes is one of them even though the inspection check sheet had no issues highlighted.

Our local Mercedes dealer advised the brakes are performing fine even though the pedal is making a hissing noise when released and i did mention the brake servo only to be told they have never replaced this part on a w205 c class.

I contacted Mercedes Benz customer services who said they have spoken to our local dealer who said the brakes are fine but if i wasn't happy i should have another Mercedes dealership assess them.

I have got back in touch with the dealership we purchased the car from to see if they can assess the brakes and get this issue sorted so lets see how far i get with that.

Seems to me that you have to go backwards and forwards several times before they acknowledge there is a problem and actually fix it!

Video uploaded to youtube https://www.youtube.com/watch?v=T2vLbE7QZTI

Also found this link where a video has been posted and has the same issue we are having too:

https://mbworld.org/forums/c-class-w205/765648-hissing-sound-when-letting-off-brake.html

 

[ZedC]

I have been back and forth with Mercedes Benz customer services and also the Inchcape group who we purchased our car from.

My brakes have been deemed to be operational even though the hissing noise on release has been acknowledged to be more than normally expected.

Only option i have been given by Inchcape is I can have the brake servo changed at my own cost.

Makes you question the point of buying a car with an approved warranty.

 

[Rambosouthlondon]

That is most likely a symptom of a leaking brake servo. The hissing noise is the vacuum escaping. The place where it is leaking needs to be identified and it will probably need to have the servo replaced. Not common but it does happen. It will not be cheap and can be a PITA job.
If it were me and I was being fobbed off over this I would make a short video of the sound and then write to the dealer principal suggesting to him/her that this is a serious safety issue which needs to be fixed.

What’s a pita job

 

[kendog91]

What’s a pita job

Pain in the ****

 

[Rambosouthlondon]

Mines hissing when pressed

 

[Smiley]

Mines hissing when pressed

That's more worrying; there is a leak when you really need the servo. It needs looking at asap before you lose your servo assistance.....and that will feel like you have lost your brakes.