From the earliest block against wheel system, brakes underwent a revolution, especially with the development of the automobiles in the early 1900s. The brake system has come a long way since then. In the whole evolution, Drum Brakes were the earliest and most effective systems for braking invented which is still in widespread use today.
- A stainless steel flexible band was fitted around a drum on the rear axle.
- The band was actuated by depressing the brake pedal and resulted in its gripping the drum.
However, the modern drum brake employs a cast iron drum inside which two curved shoes that matches the curvature of the drum are fitted with one end attached to a pivot and the other to the actuating rods.
The leading/trailing system employs a design in which one of the shoes is of the self applying types, usually fitted in the rear wheels.
There are minor parts such as linkage, self-adjusting components and hold down hardware making up the assembly.
In the simplest mechanical drum brake, the brake pedal transmits force to the shoes that expand and clamp against the drum resulting in stopping motion. Hydraulic drum brakes are operated a bit differently.
Drum brakes were refined with the addition of power assisted braking that used vacuum in the manifold. In the electrohydraulic system an electric motor operates the hydraulic pump and creates braking pressure. The systems were further refined with development of ABS systems.
Drum brakes, when maintained properly, works most effectively. With the right design, drum brakes can bring a vehicle to a halt quickly, especially when hydraulics are employed.
The disadvantages are that it requires a larger drum surface and larger shoe area to generate enough braking power.
Drum brakes have been in use since well over a century and will endure despite the rise of other systems because of their inherent simplicity and ease of maintenance.