W204 Brake Pedal sinks to floor

[KeithRad]

We own a 2007 C220 CDI Avantgarde Automatic. When idling say at a traffic light, the brake pedal sinks to the floor in about 10 seconds or less.

South African Vehicle Roadworthy law does not allow this, Mercedes Benz SA insist that this vehicle's brakes conform to their specifications.

If anyone has experienced a similar problem, your comment would be appreciated.

This link: http://raduehost.com/MercedesBrakeProblem/MercedesNightmare.pdf
explains the probvlem in more detail and contains a link to a 2 minute un-edited movie clip of the brake pedal going to the floor.

 

[television]

This is an interesting post as we had one here a few days back with the same problem

http://forums.mercedesclub.org.uk/showthread.php?t=82690&highlight=brake+sinking

 

[dieselman]

I don't think the pedal is going all the way to the floor as occasionally it goes further than you normally press. I wonder if the pushrod to the master cylinder it correctly adjusted so you get the knocking sound.

What happens if you just press and keep pressing without letting up at all and what if you do it with the engine off and servo vacuum already depleted?

 

[television]

I don't think the pedal is going all the way to the floor as occasionally it goes further than you normally press. I wonder if the pushrod to the master cylinder it correctly adjusted so you get the knocking sound.

What happens if you just press and keep pressing without letting up at all and what if you do it with the engine off and servo vacuum already depleted?

I do not think that the push rod is adjustable

 

[KeithRad]

Thanks for the response so far,

I measured pedal movement yesterday as follows (measured the lower end of the pedal - where my foot would be to the floor)

Brake pedal Movement
1 April 2011

A) Engine Off:
No pedal pressure - distance to floor 16 cm
Light pressure - distance to floor 12 cm
Medium pressure - distance to floor 10.5 cm
Hard pressure - distance to floor 6.5 cm

B) Engine on:
No pedal pressure - distance to floor 16 cm
Light pressure - distance to floor 6 cm

 

[KeithRad]

This problem has been cross posted to

http://www.mbworld.org/forums/c-class-w204/394389-w204-brakes-fail-roadworthy-benz-says-normal.html

The German forum has a post with a serious W204 brake failure involving an accident.

PLEASE all C class owners check your brakes - this could save someones life.

Keep a gentle continuous pressure on your brake pedal while starting your vehicle. If the brake pedal sinks down more than a couple of centimetres, you may have a problem.

Mercedes Benz in South Africa continue to deny that there is a brake problem, in spite of the fact that our car failed a roadworthy test because of the sinking brake pedal.

 

[Wilko_UK]

Brake Pedal Fade

I had something similar to this on my C220 CDI. Turns out the master cylinder had failed - not as bad as your case tho. So although there was vacuum, clean brake fluid, new pads etc, with nothing to compress the hydraulics the pedal just went to the floor.

However, Television knows his stuff if he can't solve it, no one can.

 

[Rinehart]

Brake fade

I have a 1991, R129, 300SL, 103Kmiles that experienced the same problem. After installing new front rotors, brake pads, (rear brakes were checked and found okay) bleeding and flushing the system twice the problem still persisted. The problem was finally solved by the installation of a new
Master Cylinder .
The bore's of the master cylinder are quite small (as compared to a chevy).
The pressures are intense leading to premature failure, depending on fluid flush and abnormal servicing of the brake system.
Good luck in solving your problem.

 

[Alex Crow]

as above, it can only be the master cylinder.

i disagree about premature failure, it is very unusual to change one on any MB car built in the last 20 years. this does not include the w204 series problem of course!

 

[KeithRad]

Thanks Alex and all others for your valued input so far,

The master cylinder is the obvious cause of the problem and was replaced by the m/b dealer.

When this never fixed the problem, escalation was to Mercedes Benx South Africa.

This is the last insult to my intelligence I received late on Friday 1 April 2011 from them.

 

[Alex Crow]

OK, it is just possible that there is pressure loss through the electrohydraulic unit, and it is also possible that the BS sounding letter is genuine and the car is OK. it is MB's problem getting it through the vehicle inspection (now you have a letter saying the car has no faults and is as designed) but you will struggle to get any further esponse without escalation - i guess this is why you are here...

i must add that this problem used to come up with the 107 and 116 fitted with a particular servo setup, pedal travel seemed excessive when stationary, but was always OK when in normal use. the MOT stations eventually got used to it, but it caused a few niggles getting them through.

 

[dieselman]

The absolute test would be to disconnect the pipes after the master cylinder and blank them off, then apply the brake pressure, the pedal should remain solid with no sinkage.

 

[KeithRad]

I guess this would not be so serious if we had not experienced a real life brake failure when my better half was proceeding carefully (as the ramp was wet) into an underground parking in the middle of Johannesburg and was almost at the second level when the car "lurched" forward for several metres. Lucky for her there was nothing in her path and she kept control of the vehicle in spite of the brake pedal being down on the floorboards. A quick pump and the brakes were back.

 

[television]

What one must consider here is that MB cannot say there is a fault as it could cause huge problems, they will work away at this and possibly do a recall, this is the last thing that any car manufacturer wants owing to the cost and the publicity

 

[KeithRad]

Thankyou to all who have shown interest in my problem.

Over two weeks have now elapsed and our car is still in my garage at home and is still not roadworthy!

Please see my website www.raduehost.com for up to date information.

I will also post here when there are any new developments.

Keih