The Hydraulic System

Master Cylinder

The master cylinder is actually two completely separate master cylinders in one housing, each one handling two wheels. This way, if one side fails, you will still be able to stop. The most common problem is leaking. This will cause the brake pedal to slowly sink to the floor when you apply steady pressure to the brake pedal.

Brake Lines

The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses. Rubber hoses are only used in specific places that require flexibility.

Proportioning Valve

This is also called an equalizer valve. They are designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping. The shorter time you stop, the more of the vehicle's weight is transferred to the front wheels, which can cause the rear to lift. These valves are designed to direct more pressure to the front and less pressure to the rear when you stop quickly.

Pressure Differential Valve

This is usually mounted below the master cylinder and is responsible for turning the brake warning light on when it detects a malfunction. It measures the pressure from the two sections of the master cylinder and compares them. If it detects a difference between them, there is probably a brake fluid leak somewhere in the system.

Power Brake Booster

This is connected directly to the brake pedal and is designed to amplify the available foot pressure that is applied to the pedal. A check valve is connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the booster but does not let it escape. If the engine stalls while you are driving, you will have a small reserve of power assist for two or three pedal applications, after which you will have to apply significant pressure to the pedal to bring the vehicle to a stop.