Drum brake is also called block braking, which is realized by pressing the brake block on the brake wheel. Drum brake is the early design of the brake system, the design of its brake drum in 1902 has been used in the carriage, until about 1920 began to be widely used in the automotive industry. Now the mainstream of the drum brakes is the internal tension, its brake block (brake shoe) is located on the inside of the brake wheel, and the brake block opens outwards when it is on the brakes, and friction the inside of the brake wheel to achieve the purpose of braking.

　　Compared with disc brake, the brake efficiency and heat dissipation of drum brakes are much worse. The brake force stability of drum brakes is poor, and the braking force on different roads varies greatly and is not easy to control. Due to the poor heat dissipation, a lot of heat will be gathered during the braking process. Brake blocks and wheel drums are prone to extremely complex deformation under high temperature, which are likely to cause brake degradation and trembling, resulting in a reduction in braking efficiency. In addition, after a period of time, the drum brake should be regularly adjusted to the clearance of the brake shoe, and even the whole brake drum should be removed and the brake powder accumulated and accumulated. Of course, drum brakes are not useless. They are cheap and conform to traditional designs.

　　The four wheel car in the braking process, because of the inertia, the load of the front wheel usually accounts for the 70%-80% of the full load of the car, the front wheel brake force is bigger than the rear wheel, the rear wheel is auxiliary braking, so the car manufacturer uses the brake square of the front disc and rear drum in order to save the cost. However, for heavy vehicles, because the speed is generally not very high, the brake shoe is more durable than the disc brake, so many heavy cars still use the design of the four wheel drum type.

　　The working principle of the drum brake is basically the same as that of the disc brake: the brake shoe holds the rotating surface. This surface is called a drum.

　　The rear wheels of many cars are equipped with drum brakes, and the front wheels are equipped with disc brakes. Drum brakes have more components than disc brakes and are more difficult to repair, but the manufacturing costs of drum brakes are low and easy to be combined with emergency braking systems.

　　Like disc brake, drum brakes also have two brake shoes and one piston. But the drum brakes also have a regulator mechanism, an emergency brake mechanism and a large number of springs.

　　When you step on the brake pedal, the piston pushes the brake shoe against the drum. This is easy to understand, but why do we need these springs?

　　This is where the drum brakes are more complex. Many drum brakes are self - acting. When the brake shoe contacts with the drum, there will be some wedge action. The effect is to press the brake shoe into the drum with greater braking force.

　　The additional brake force provided by the wedge action, can make use of the drum brake disc brake piston than with smaller.

　　However, due to the presence of a wedge action, to release the brake, brake drum must make out. That's why some springs are needed. Other springs help to fix the brake shoe in place and return it after the adjusting arm is driven.