Brake Proportioning/Combination Valve: Testing and Inspection
WARNING LIGHT SYSTEMIf the parking brake light is connected into the service brake warning light system, the brake warning light will flash only when the parking brake is applied with the ignition turned on. The same light will also glow should one of the two service brake systems fail when the brake pedal is applied.
To test the system, turn the ignition on and apply the parking brake. If the lamp fails to light, inspect for a burned out bulb, disconnected socket, a broken or disconnected wire at the switch.
To test the brake warning system, raise the car and open a wheel bleeder valve while a helper depresses the brake pedal and observes the warning light on the instrument panel. If the bulb fails to light, inspect for a burned out bulb, disconnected socket, or a broken or disconnected wire at the switch. If the bulb is not burned out, and the wire continuity is proven, replace the brake warning switch.
PROPORTIONING VALVE
On vehicles with Bosch ABS-3, Bendix Anti-Lock 6 or Bendix Anti-Lock 10, refer to Anti-Lock Brake System for testing procedures.
If premature rear wheel skid occurs on hard brake application, it could be an indication of a malfunctioning proportioning valve unit.
The proportioning valve is designed with two separate systems. One half controls the right rear brake, and the other half controls the left rear brake. A road test to determine which rear brake slides first must be performed.
Fig 32 Type 1 Combination Valve Pressure Gauge Test Connections. Right Wheel Malfunction:
1. To test proportioning valve when right rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
a. Install gauge set tool No. C-4007A, or equivalent, as shown. A special adapter may be fabricated from a short piece of brake tube and two 3/8 X 24 tube nuts.
b. Bleed the hose and gauge set.
c. While watching pressure gauges, have an assistant depress the brake pedal. Note gauge readings, then refer to "Hydraulic Brake Controls Specifications" chart.
2. To test proportioning valve when left rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
Fig 33 Type 1 Combination Valve Pressure Gauge Test Connections. Left Wheel Malfunctions:
a. Install gauge set tool No. C-4007A, or equivalent, as shown. A special adapter may be fabricated from a 7/16 X 24 tube nut, a short piece of brake tube and a 3/8 X 24 tube nut.
b. Bleed hose and gauge set.
c. While watching pressure gauges, have an assistant depress the brake pedal. Note gauge readings, then refer to Hydraulic Brake System/Specifications.
3. If pressure readings are not as specified for left or right rear wheel, replace the combination valve noting the following:
a. After installing a new combination valve, bleed hydraulic brake system as described under Hydraulic System/Service and Repair/Brake System Bleed.
b. After bleeding brake system, reset brake warning switch by depressing brake pedal with moderate force. Brake warning lamp will turn off when switch is reset.