Hydraulic System: Description and Operation

Hydraulic Brake Actuation
The hydraulic brake system consists of:
^ the vacuum brake booster (E-150, E-250 and E-350).
^ the Hydro-Boost(R) brake booster (E-450).
^ the brake master cylinder.
^ the front disc brake calipers.
^ the rear disc brake calipers.
^ the anti-lock brake system (ABS) components.
^ the brake tubes and hoses.

Brake Fluid

WARNING: Carefully read cautionary information on product label. For EMERGENCY MEDICAL INFORMATION seek medical advice. In the USA or Canada on Ford/Motorcraft products call: 1-800-959-3673. For additional information, consult the product Material Safety Data Sheet (MSDS) if available. Failure to follow these instructions may result in personal injury.

CAUTION: Brake fluid is harmful to painted or plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it off with water.

Use only clean, fresh DOT 3 motor vehicle brake fluid in the hydraulic brake system.
^ Do not reuse the brake fluid drained or bled from the system.
^ Do not use brake fluid that has been stored in an open container.
^ Do not use contaminated brake fluid.
^ Do not mix different types of brake fluid.

Brake Master Cylinder
The brake master cylinder is a dual-piston type containing a primary and a secondary piston. When the brake pedal is applied, a mechanical linkage applies force to the brake booster. The brake booster multiplies the force applied to the brake pedal and transmits the multiplied force to the brake master cylinder pistons. The brake master cylinder pistons transmit the force applied to the hydraulic brake fluid. The pressure created by the force of the hydraulic fluid is directed to the wheel brake assemblies through the brake lines and hoses. This hydraulic pressure then forces the brake caliper pistons outward against the brake pads and the brake pads against the brake rotor friction surfaces, slowing the wheel speed. When the brake pedal is released, the hydraulic force is removed, allowing the brake pads to retract slightly from the brake rotor friction surface and allowing the wheels to rotate.

On speed-control equipped vehicles, the brake master cylinder has a speed control deactivator switch located on the underside of the brake master cylinder casting which acts as a redundant safety device. Refer to Cruise Control.

Brake Master Cylinder Reservoir

NOTE: Whenever the brake master cylinder reservoir is to be repaired, a new master cylinder must be installed.

The brake master cylinder reservoir holds a supply of brake fluid for the master cylinder and the brake hydraulic system. The master cylinder reservoir is mounted to the top of the master cylinder and is sealed to the master cylinder body with grommets. The master cylinder reservoir has visual fluid markings allowing fluid level inspection without removal of the reservoir cap. The master cylinder reservoir contains a brake fluid level sensor. The brake fluid level sensor is a magnetic reed switch which, when the fluid drops to a predetermined level, will activate the red brake warning lamp on the instrument cluster. For information on the red brake warning lamp, refer to Instrument Panel, Gauges and Warning Indicators.

Brake Tubes and Hoses

CAUTION: Never use copper tubing to replace hydraulic brake line. Copper may fatigue, crack or corrode, which could result in brake line failure.

The brake tubes and hoses transmit the hydraulic pressure to the wheel brake assemblies.

All brake tubes must be correctly double-flared to provide strong, leak proof connections. When bending brake tube to fit the underbody or rear axle contours, be careful not to kink or crack the brake tube.

When routing a brake tube, allow 51 mm (2 inch) of clearance between the brake tube and the exhaust system or any moving components.

If a section of brake tube is damaged, the entire section must be replaced with a brake tube of the same type, size, shape and length as originally installed.

When installing new hydraulic brake tubes, hoses or connectors, tighten all connections securely. When the installation is complete, bleed the brake system.