When the brake pedal is depressed, the force is transmitted via the push rod to the master cylinder where the piston is pushed.
The force of the hydraulic pressure generated inside the master cylinder is transmitted via the brake lines to the each wheel cylinder.
1. Normal operation
(1) When the brakes are not applied.
The piston cups of No.1 and No.2 piston are positioned between the inlet port and the compensating port, providing a passage between the master cylinder and the reservoir tank. No.2 piston is pushed to the right by force of No.2 return spring, but prevented from going any further by a stopper bolt.
(2) When the brake pedal is
No.1 piston moves to the left and the piston cup seals the compensating port to block the passage between the cylinder and the reservoir tank. As the piston is pushed farther, it increases the hydraulic pressure inside the master cylinder. This pressure acts on the rear wheel cylinders. Since the same hydraulic pressure also pushes No.2 piston, No.2 piston operates in exactly the same way as No.1 piston, and acts on the front wheel cylinders.
(3) When the brake pedal is released.
The pistons are returned to their original position by hydraulic pressure and the force of the return springs. However, because the brake fluid does not return from the wheel cylinder immediately, the hydraulic pressure inside the master cylinder momentarily drops (a vacuum develops). As a result, the brake fluid inside the reservoir tank flows into the master cylinder via the inlet port, through many orifices provided at the tip of the piston, and around the periphery of the piston cup. After the piston has returned to its original position, the brake fluid that gradually returns from the wheel cylinder to the master cylinder flows into the reservoir tank through the compensating ports. The compensating port also absorbs changes in brake fluid volume that could occur inside the cylinder due to temperature changes. This prevents the hydraulic pressure from rising when the brakes are not being used.
2. If fluid leaks in one of the systems.
(1) Fluid leakage in rear side When the brake pedal is depressed, No.1 piston moves to the left but does not create hydraulic pressure in the rear side. No.1 piston therefore compresses the return spring, contacts No.2 piston, and pushes it No.2 piston increases hydraulic pressure in the front end of the master cylinder, which allows two of the brakes to be operated from the front of the master cylinder.
(2) Fluid leakage in front side
Since hydraulic pressure is not generated in the front side, No.2 piston advances until it contacts the wall at the far end of the master cylinder. When No.1 piston is pushed farther to the left from this position, hydraulic pressure increases in the rear side of the master cylinder, which allows two of the brakes to be operated from the rear of the master cylinder.