Base Brake System

DESCRIPTION
The base brake system consists of the following components:
- Brake pedal
- power brake booster
- brake tubes and hoses
- proportioning valves
- disc brakes
- drum brakes
- brake lamp switch
- brake fluid level switch
- parking brakes
Front disc brakes control the braking of the front wheels; rear braking is controlled by rear drum brakes as standard equipment. Rear disc brakes are optional.
The hydraulic brake system is diagonally split on both the non-antilock and antilock braking systems. This means the left front and right rear brakes are on one hydraulic circuit and the right front and left rear are on the other.
Vehicles equipped with the optional Antilock Brake System (ABS) use a system designated Mark 20i. This system shares most base brake hardware used on vehicles without ABS. A vehicle equipped with ABS, however, uses a different power brake booster, master cylinder, and brake tubes. Also included in the ABS system is an Integrated Control Unit (ICU), four wheel speed sensors, and an electronic controller referred to as the Controller Antilock Brake (CAB). These components are described in detail in Brakes, Antilock Brake System.

OPERATION
When a vehicle needs to be stopped, the driver applies the brake pedal. The brake pedal pushes the input rod of the power brake booster into the booster. The booster uses vacuum to ease pedal effort as force is transferred through the booster to the master cylinder. The booster's output rod pushes in the master cylinder's primary and secondary pistons applying hydraulic pressure through the chassis brake tubes and proportioning valves to the brakes at each tire and wheel assembly.
The parking brake is hand-operated. When applied, the parking brake lever pulls on cables that actuate brake shoes at each rear wheel.