Brake cylinders are central components of hydraulic braking systems

Hydraulic brakes have become standard for service brakes in cars and motorcycles. Only parking brakes are still designed with mechanical cable solutions. Brake cylinders are central components of hydraulic braking systems.

Position and Function of Brake Cylinders

A vehicle always has as many brake cylinders as it has wheels, plus at least one. A distinction is made between wheel brake cylinders and the master brake cylinder.

The master brake cylinder is located on the brake booster

This doubles the muscle power arriving from the pedal. For this purpose, a permanent vacuum is generated in the brake booster. When the braking process is initiated, normal air pressure provides the desired amplification.

The master brake cylinder consists of a simple piston that moves in a bushing with five openings. The main opening ensures the inflow of brake fluid. The four laterally mounted bores transmit the brake pressure to the wheel brake cylinders. The transmission of brake pressure occurs through largely rigid lines. Only shortly before the connection to the wheel brake cylinders does the rigid brake line transition into a flexible brake hose. However, this is only laterally movable. Internal reinforcement ensures that the brake hose cannot expand.

Wheel Brake Cylinders in Disc Brakes and Drum Brakes

In disc brakes, wheel brake cylinders are located in the brake caliper. They have a large cross-section but only a few millimeters of travel. Via a deflection mechanism, the single-acting wheel brake cylinders press the brake pads located in the brake caliper against the brake disc on both sides with uniform pressure.

In drum brakes, these components are designed as double-acting cylinders. They push the brake shoes apart, which then press against the inside of the brake drum.

This achieves the desired deceleration.

Brake Cylinder Defects

Brake cylinders in vehicles are exposed to high stresses. In addition to high pressures, weather, abrasion, and fluctuating temperatures contribute to the wear of brake cylinders.

In the master brake cylinder, the seals can fail over time. This severely reduces braking effectiveness, and the driver feels like they are pressing into “nothing.”

In the wheel brake cylinders of disc brakes, penetrating dirt and corrosion can cause the pistons to seize. The driver notices this when the car pulls to one side during braking.

Both driving situations are extremely dangerous. In such cases, vehicles should be safely parked and transported to the nearest workshop by a tow truck.

Wheel brake cylinders of disc brakes and master brake cylinders can theoretically be repaired and overhauled. However, this is only worthwhile if there are problems with procuring replacement parts. This is the case, for example, with classic cars.

Caution: Overhauling used brake calipers and master brake cylinders should only be carried out by qualified specialist companies!

Wheel brake cylinders of drum brakes, on the other hand, are very small and therefore fundamentally designed as replacement parts. There are no possibilities for overhauling them.