Older Mercedes have a very effective emergency brake design which was virtually the same on all models from the late 1960s right up through the early 1990s. The actuating mechanisms are all mechanical and are controlled by a Y cable under the car. This cable is pulled by either a hand or foot operated lever.
The actual brake mechanism looks just like an old style twin-shoe drum brake assembly and is mounted inside the hub of each rear brake rotor. When the cable is pulled the twin shoe assembly is spread apart and binds against the surface of the drum. Adjustment is performed by turning a star wheel nut inside the brake rotor. On many models there is also an adjusting bolt at the Y in the cable to take up slack, if adjusting the star nut does not give the desired results.
Emergency brake shoe linings can last for years and require very little maintenance. Their life span is determined by total age and mileage of the car, exposure to water and road salt, and how many times the emergency brake has been accidentally engaged while driving! If your Mercedes is over 10 years old or has more than 150,000 miles then I recommend you inspect the emergency brake mechanism inside the rear rotor. If you see a lot of evidence of rust in and around the rear end then I would definitely inspect them as soon as possible.
This 10 page manual (8.5x11 format) will take you through the process of inspecting your emergency brake system, removal and replacement of your emergency brake shoes and springs, and proper adjustment procedures. Manual is also available in a PDF download version if you would prefer, please see below.