All You Need to Know About Brake Master Cylinder in Vehicles

All You Need to Know About Brake Master Cylinder in Vehicles


The master cylinder, also known as the brake master cylinder, transforms the pressure on the brake pedal to hydraulic pressure by distributing the brake fluid to the brake circuit. Master brake cylinders are used in both disc brakes and drum brakes.

According to legal regulations, a vehicle must have two separate brake circuits. Back-to-back master cylinders create hydraulic pressure for two different brake circuits. If one of the brake circuits does not work, the brake pressure is made with the other circuit operating.

When the driver presses the brake pedal, the force of his foot on the pedal is conveyed to the pressure piston. The piston is pushed against the brake line.

In older vehicle models, in the master cylinder, the piston ring passes over the balancing hole, and the pressure chamber is closed, and braking force is obtained. When the driver releases the brake pedal, the pressure piston returns to its original position. Brake fluid flows into the master cylinder, increasing the brake pressure if the pedal is suddenly pressed again.

Brake master cylinders on new vehicles

New vehicles with brake master cylinder ESP® do not have compensation holes and replenishment points. The center valves perform the duties of these components.

When the master brake cylinder is in neutral, the central valve is open. The volume compensation between the brake fluid reservoir and the wheel brake is achieved through the fill point and piston bores.

The central valve is closed when the brake is applied, breaking the connection between the brake fluid reservoir and the wheel brake. The pressure now starts to build up again. Closing the central valve is equivalent to the primary collar passing over the balancing hole in the brake master cylinder with such a hole.

Releasing the brakes

After the brake pedal is released, the pressure in the circuit drops, and the wheel brakes are released. Returning to its neutral position, the piston creates a vacuum, which opens the center valve, thus allowing the brake fluid to be filled. After the release is complete, the neutral position is achieved, and the center valve remains open.


Brakes are one of the most effective safety systems of the vehicle. They have been used hundreds if not thousands of times a day without the driver noticing. The driver usually brakes deliberately only if braking does not follow the usual procedure. For safety reasons, only back-to-back master cylinders are used today. If a cylinder circuit of the cascade master cylinders fails, pedal play increases during braking. If this occurs, it must be shown to the service.


Brake master cylinders from well-known suppliers are made of premium materials that provide reliable protection against corrosion, thus ensuring optimal longevity and functioning of the master cylinder. It is essential to regularly check and replace the brake fluid for the life of the entire brake system. In addition, the vent hole in the filling chamber must be clean and kept open. This hole must be closed before cleaning the engine so that water does not penetrate.