Brake master cylinder: common defects and their signs

1. Damaged piston return spring.
   • Brake pedal doesn’t react to pressing at once.
   • Sometimes the pedal is jammed.
   • The car deflects aside when braking.
   • Wheels slow down on the move while the brake pedal is not pressed.
2. Soiling or complete clogging of the compensating port.
   • The brake pedal doesn’t return into position after being pressed.
   • Pedal working travel decreased.
3. Worn out sealings.
   • Working travel of the brake pedal increased.
   • Leaks of working liquid near the component.
   • The braking liquid level control light comes on.

How to repair or replace brake master cylinder?

Repair of the brake master cylinder implies replacing all the sealings. It can be performed on your own if you buy a special kit beforehand. The work order is the following:

1. Turn off voltage supply from the battery.
2. Disconnect all wires from the braking fluid level sensor.
3. Drain braking fluid from the tank.
4. Unscrew the nuts which fasten brake pipes and those fastening the brake master cylinder to the brake vacuum booster.
5. Drain braking fluid from the tank and then demount the brake cylinder with the tank.
6. Disassemble it, wash it and clean all the elements.
7. Make sure there are no mechanical damages of the housing or inner surface. Otherwise the component is to be replaced.
8. Perform replacement of all sealings, assemble the brake cylinder and install it on the car.

If the defect is not in worn sealings, the brake master cylinder should be replaced in assembly. To do this yourself, perform the following actions:

1. Demount the brake master cylinder according to the algorithm described above.
2. Install a new component into position and reassemble all the elements.
3. Fill the tank with braking fluid.
4. Flush brake system after installing.

When installing a new cylinder, it is recommended to install new sealings between the cylinder and the tank. The process can differ a little for cars of different brands, so consult technical documentation before replacement.