Ford 2003 Mustang Workshop Manual page 617

Brake Pressure Control Valve
The brake pressure control valve proportions the pressure to the rear brakes.
When the brake pedal is applied, brake fluid pressure passes through the proportioning valves
to the rear brake system until the valve split point is reached.
Above its split point, the proportioning valve begins to reduce the hydraulic pressure to the rear
brakes, creating a balanced braking condition between the front and rear brakes.
Brake Tubes and Hoses
CAUTION: Never use copper tubing. It is subject to fatigue, cracking and corrosion which
could result in brake tube failure.
Steel tubing is used throughout the brake hydraulic system. All brake tube fittings must be correctly
double flared to provide strong leakproof connections. When bending the tubing to fit the underbody or
rear axle contours, be careful not to kink or crack the tube.
If a section of brake tube is damaged, the entire section must be removed and a new tube of the same
type, size, shape and length installed.
When replacing hydraulic brake tubing, hoses, or connectors, tighten all connections securely. After
installation, bleed the brake system. For additional information, refer to Section 206-00 .