Brake Master Cylinders & Reservoirs


Brake Master Cylinders: Explained

Brake master cylinders transform the applied force on the brake pedal into hydraulic pressure by sourcing fluid from the reservoir and feeding it into the brake circuit. The process is controlled through mechanical force.

Types of Brake Master Cylinders

There are two types of master cylinders including the simple and tandem versions. The difference lies in the number of pistons each cylinder contains. Simple cylinders include only one piston, while tandem cylinders integrate two pistons which generate more braking power through higher hydraulic pressure.

What are Integral Reservoir Master Cylinders?

Integral reservoir master cylinders incorporate a reservoir and a precisely engineered cylinder in one piece to increase efficiency and performance. They feature a slim aluminum design, anodized finish and dual mounting bolt systems which makes them suitable for racing cars. Their exterior return spring guarantees a strong pedal feel and decreases pad wear. Most applications integrate built in fill tabs which allow you to easily check fluid levels. However, a special category includes the race car master cylinders which are specifically engineered to withstand the extreme requirements and conditions of F1 or rally competitions. They’re lightweight and made of aluminum alloy and their lean design makes them easy to install in race cars where space is extremely limited.

How do Master Cylinders and Reservoirs Work?

All modern cars include twin hydraulic circuits and two master cylinders which produce hydraulic pressure in turn in case one of them shuts down. Depending on the car manufacturer, one circuit controls the rear brakes and the other one the front brakes, or one circuit controls all four brakes and the other only the front brakes or each circuit controls one rear brake and the two front brakes. If one of the circuits fails due to a leak, the pressure between the primary and secondary cylinders instantly decreases. This leads to contact between the primary and secondary cylinders and in turn the brake master cylinder will behave as if it only has one piston. Although the second circuit is intact, you’ll have to press harder on the brake pedal to activate it. However, the brake power will be significantly lower than normal. In neutral position, the replenishment port and bore holes of the piston achieve the compensation between the wheel brake and the fluid reservoir. The central valve closes when the brake is activated and interrupts the link between the wheel brake and the reservoir resulting in an increase of pressure. When you release the pedal, the circuit’s pressure decreases which in turn releases the wheel brakes. When the piston returns to neutral it creates a vacuum which allows for the brake fuel to replenish via central valve which is open.

Checking the Brake Fluid Level

To maintain the proper functioning of your car’s brake system you should regularly check and replace the brake fluid. Also, you should keep the ventilation hole on top of the reservoir as clean as possible to prevent contaminants from penetrating into the fluid. To check the fluid level in the reservoir you should check the line on the dipstick and make sure it’s between add and full. If it’s below the add mark, then you probably have a leak in the brake system. You should also verify if the liquid is clear or dark. Dark fluid is an indication that it’s contaminated, and you should get the system flushed.


The brake system is a crucial component which determines a car’s safety levels. That’s why manufacturers only integrate tandem master cylinders in today’s vehicles. If one of the brake circuits fails, the other will take over and prevents any incidents. Although master brake cylinders are made from top-quality materials they can depreciate in time. You should regularly check your car’s braking system to ensure its functions at optimal levels and to avoid any accidents.

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