http://www.eurobzparts.com/mercedes-benz-brake-booster/

The brake booster increases the power used to the master cylinder that provides an upgrade in the overall braking power. In essence, the brake booster can stop your Mercedes without using a large amount of force. This upgrade works hard enough drawing on a vacuum from the engine in its entire operation. Unlike the car brake that has its own system, this booster uses the engine as power source. The Brake Booster is located on the Mercedes Benz firewall at the master cylinders’ firewall in which it is attached to the brake pedal.