Mercedes-Benz C-Class (W204) 180 Compressor brake pressure issues

[NicoMercedes]

I'm wondering if someone could offer some advice on a 2007 Mercedes-Benz C-Class 180 Compressor automatic (W204).

Two weeks ago, I experienced a sudden loss of brake pressure when the engine was idling or the car was rolling. However, when I started driving, the brake pressure returned to normal and worked fine.

After coming to a complete stop, if I let the car roll a bit, the brake pedal becomes stiff at the top with very little or no pressure. Once I start driving again, everything works fine until the next stop. If I turn on the engine and let the car roll, there is still no pressure with a stiff pedal.

I've had the car serviced, and no vacuum leaks were found, and the brake fluid is full. The mechanic suspects that the issue may be with the failing master cylinder or the pump located behind the engine, but they are not entirely sure.

Any input welcome

 

[ernie]

I'm wondering if someone could offer some advice on a 2007 Mercedes-Benz C-Class 180 Compressor automatic (W204).

Two weeks ago, I experienced a sudden loss of brake pressure when the engine was idling or the car was rolling. However, when I started driving, the brake pressure returned to normal and worked fine.

After coming to a complete stop, if I let the car roll a bit, the brake pedal becomes stiff at the top with very little or no pressure. Once I start driving again, everything works fine until the next stop. If I turn on the engine and let the car roll, there is still no pressure with a stiff pedal.

I've had the car serviced, and no vacuum leaks were found, and the brake fluid is full. The mechanic suspects that the issue may be with the failing master cylinder or the pump located behind the engine, but they are not entirely sure.

Any input welcome

Are you sure the C180, petrol has a separate vacuum pump? The diesels definitely do but I'm not so sure about the petrols. Assuming that there is no pump, I'm thinking along the lines of a leak in the vacuum reservoir which may be attached to the master cylinder; also some systems have a non-return valve in the vacuum line from the engine, which, if sticking, may be causing your loss of vacuum.

Sorry to be not much help, but somebody who knows the system used in your car should be along to give more help.

Ernie