Brake Master Cylinders

Does the pedal slowly sink to the floor under constant pressure, or does your project need a different bore than the original? This category brings together brake master cylinders for cars and motorcycles, e.g. model-specific cylinders from DFC and motorcycle cylinders from Brembo Powersports.

What the master cylinder does

The master cylinder converts the force from the pedal or lever into hydraulic pressure in the brake system. The bore diameter affects the relationship between travel and force. A smaller bore typically gives higher pressure for the same force, but longer travel. A larger bore gives shorter travel and requires more force. The right balance depends on the piston area of the brake calipers and whether a brake booster is fitted. The part belongs under master cylinders and brake boosters.

How to choose a master cylinder

• Bore: e.g. compact cylinders with a 3/4" bore are available from BLOX Racing.
• Mounting and connections: number of bolts, port position (e.g. right-hand port) and thread type must match the car and brake lines.
• Circuits and ABS: check whether the car requires a tandem cylinder and whether the ABS system has special requirements.
• Car or motorcycle: e.g. cylinders from Brembo Powersports are available for the Aprilia RSV4 in a right-hand version for the handlebar.

Brands in the category include DFC, Baer Brakes, Performance Machine and OMIX.

Installation and maintenance

A new master cylinder should typically be bench bled before it is installed. The entire system must then be bled. Use the type of brake fluid specified by the manufacturer. If the fault is caused by worn seals in an otherwise usable cylinder, a master cylinder rebuild kit can be an alternative. Changes to the brake system can matter at a roadworthiness inspection. Therefore, check the approval for the specific part number and your car.

Frequently asked questions

How do I know if the master cylinder is faulty?

A pedal that slowly sinks under constant pressure can be caused by an internal leak in the master cylinder. A soft pedal can also be caused by air in the system or boiling brake fluid. So have the fault diagnosed before you replace the part.

Should I choose a larger or smaller bore?

It depends on the brake calipers, the booster and the pedal feel you want. A smaller bore typically gives a lighter but longer pedal. A larger bore gives a shorter and heavier pedal. Match your choice to the rest of the brake system.

Does a new master cylinder require approval for inspection?

It depends on the product and the car. A model-specific replacement is something different from a conversion with a different bore. Check the requirements and any documentation for the specific part number before fitting the part to a registered car.