4. Proportioning Control Valve Function

70M 0111

• A Master cylinder
• B Chamber B
• C Chamber A
• D Caliper
• E Piston
• F Chamber C
• G Sleeve
• H Cut-off valve
• I Slide piston
• J Spring

When the anti-lock brake system is functioning, the piston moves upward, the volume of chamber B increases, and the fluid pressure on the caliper side is reduced. At the same time, the volume of chamber A is reduced and the brake fluid is returned to the master cylinder. When the brake fluid is pushed back to the master cylinder, the driver can feel the anti-lock brake system is operating because the brake pedal is kicked back.

4. Proportioning Control Valve Function

In the modulator for the rear wheels, the diameters of the piston and the slide piston are distinctly different. This provides a proportioning control valve function to prevent the rear wheels from locking during an emergency stop.

(1) Before the spring force is overcome:

1. When the fluid pressure from the master cylinder is less than the force exerted by the slide piston on the spring, the cut-off valve will always be pushed downward.

Under these conditions, there is a gap between the cut-off valve shoulder and the sleeve. Chamber A and Chamber B are therefore connected through the gap. The pressure from the master cylinder flows into the rear calipers through chamber A and chamber B.