Master cylinder

FREE PLAY

And this is where the foot pedal's "free play" comes from. It is absolutely necessary that there be some amount of clearance, otherwise the seals may be pushed forwards enough to prevent the intake/return ports from ever opening up again to allow excess pressure to vent to the reservoir.

The factory manual for my car specifies 1mm to 5mm clearance.

What fluid to use?
 Always use the same as recommended of one D.O.T over, just never go below.

Function of master cylinder
A master cylinder is an automotive device that applies hydraulic pressure to the braking system. The master cylinder is typically located in the engine compartment and is fitted with a removable cap to add brake fluid.

Applies Pressure to Brakes

·         A brake master cylinder converts pressure from the brake pedal into hydraulic power that causes the brakes on an automobile to operate. The master cylinder works in a similar manner to a syringe; as pressure is applied, the brake fluid is pushed out of the cylinder toward the brakes.

Brake Safety

·         Most brake master cylinders have two chambers that each operate a set of wheels. Master cylinders are designed in this way in case of a failure in the brake system from a broken brake line or other problem. If the brakes serving one set of wheels fail, the other set will still have powered brakes.

Stores Excess Fluid

·         A reservoir is built into master cylinders to hold excess brake fluid. When the brakes are applied the fluid is forced into the brake line, causing the brakes to operate. When the brake pedal is released the fluid is allowed to escape back into the reservoir, releasing the brake system.