My brake pedal losses pressure?

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rhjcamp

Active Member
Joined
Apr 13, 2008
Messages
60
Location
Essex
Car
R-Class, & R171
Hi,
I have a Mercedes R Class 2007, 36,000 miles on the clock.

With the engine running, and the car stationary, if I press the brake pedal hard, and keep a constant pressure it will carry on moving until it hits the pedal stop?

If I pump the brakes three or four times, and then try and do the same, it still does the same.

The brake fluid is full, there is no fluid leakage on any calliper that I can see, I am pretty sure the brake fluid has never been changed as it is only 3.7 years old?

Is this normal? I am worried that if I had to do an emergency stop it would lose brake pressure, although I went out and tried a quick stop and all seemed okay?

I have also noticed that before I start the car in the morning the brake pedal is absolutely rock hard, I guess because there is no vacuum pressure in the system, but I am sure when I first got the car that there was some residual pressure which would work for one or two presses?

Anyway, am I worrying about nothing, or is this slightly suspicious?

Rob.
 
Mercedes brake fluid should be changed every 2 years :thumb:

Try that first mate
 
Hi,

I'll discuss it with MB. It has a full service history with them, so If it was due it would have been.

Thanks for the quick reply.

Rob.
 
Whoops, meant to say... so if it was due it would have been done?
 
Hard to say exactly what it is, could be many things. But it needs fixing asap.

I had one car do that because of an expanding brake flexible hose. Another went spongy because of air in the pipes (that went very hard when the brakes got hot). I assumed you have checked for leaks?

The last thing you want is a car with no brakes!
 
It will absolutely not be the fluid.

But may be a main cylinder problem.
 
Strange thing is, without the engine running, the pedal is hard, does not travel to the floor, and the brakes work....v.strange.
 
This sounds very similar to how my Sprinter brakes are, MB calls this " Progressive Braking", I even went to see a tech at MB Commercial and he told me that it is the norm. There are threads on the T1 N Sprinter Forums explaining this worrying "defect" but apparently there is nothing that can be done. If I stamp on the brakes for an emergency stop they work fine, yet if I hold the pedal down, then it creeps further and further all the way to the bottom, it used to be quite worrying, but you get used to it happening.
So, I know nothing about an R Class, but it might be that there is nothing wrong at all. I think you need to question someone in the know at MB before you worry too much and practice an emergency stop or two to give yourself some confidence that the beast will actually stop.
 
It would be very surprising on such a new car for something like the master cylinder to have failed.. Is this something that has started happening or is the car new to you?

Thanks
 
I have a similar problem on my 450sl. When on low revs the pedal sometimes goes almost to the floor , so need to sort it during winter. Pedal is rock solid with engine off , but on idle becomes spongy . Vacuum leak?:dk:
 
Been told by an mb independent that it is 'normal'. Can sombody else try it in an R class, ML or GL (They share alot of common components)
 
Do a brake bleed. It may just have some air in it.
 
MB have a fourth year 'goodwill' warranty policy, so if the car has been serviced by MB dealer up to now MB will usually offer to part-pay for faults developing in the fourth year.

I would definitely raise it with the dealer, both with regards diagnosing the problem, and possible warranty (or part-warranty) repair.
 

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