Pressure Modulator
Modulator consists of vacuum chamber, by-pass tube, end plate, air valve, by-pass valve, and pressure modulator switch. Engine vacuum is made available to modulator. Hydraulic tubing for rear brakes is routed from master cylinder, through brake warning light switch to pressure modulator, and then to rear brakes. Modulator vacuum chamber is divided into a front and rear section by a diaphragm and diaphragm plate. Diaphragm return spring holds diaphragm plate against end plate. Hydraulic cylinder is an integral part of end plate. Cylinder has one port that is connected to master cylinder and another port that is connected to rear wheels. A shutoff valve and a displacement plunger are assembled inside hydraulic cylinder. Air valve and by-pass valve are attached to end plate. Both of these valves are solenoid operated. A by-pass tube connects by-pass valve to rear of vacuum chamber. Modulator switch is spring-loaded and screws into a threaded opening in end plate. Switch breaks a circuit to provide a warning signal under certain conditions (See Warning System in this Article).