Whether block brakes on carriages and carts, scraping brakes on sledges or drum and disc brakes in passenger cars or commercial vehicles: the basic principle is always the same – using friction to achieve deceleration. The friction forces in drum brakes are generated by pressing internal brake shoes against surrounding brake drums. On road and even rail vehicles the brake shoes to do this are attached to the axles and fixed in place, whereas the drums are connected to the wheels and rotate with them.
Good protection against external influences
Drum brakes are basically differentiated according to the type of force application (cylinder, expansion wedge, S-cam), the arrangement of the brake shoes (simplex, duplex, servo) and dependency on the direction of travel (duo). The common denominator is a largely enclosed design, which offers good protection against moisture, dirt or even gritting salt. Drum brakes also exhibit good braking characteristics. In addition to their poor heat dissipation and relatively high inherent weight, however, the main reason why drum brakes are increasingly being replaced by disc brakes is their fluctuation in characteristic values (fading) that occurs under thermal load.
The drum brake most frequently used in heavy commercial vehicles is the S-cam simplex brake, or S-cam brake in short. Typical application examples are construction and off-road vehicles that operate under extreme terrain and climate conditions.