Brake Proportioning/Combination Valve: Testing and Inspection
LESS ANTI-LOCK BRAKE SYSTEMIf 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.
1. If right rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
Fig 43 Type 4 Proportioning Valve Pressure Gauge Test Connections. Right Wheel Malfunction Less ABS:
a. Install one gauge of set tool No. C-4007A, or equivalent, between brake line from master cylinder secondary port and brake valve assembly.
b. Install second gauge of set tool No. C-4007A, or equivalent, as shown. A special adapter may be fabricated from a short piece of brake tube and one 3/8 X 24 tube nuts and one M10 X 1 tube nut.
c. Bleed the hose and gauge set.
d. While watching pressure gauges, have an assistant depress the brake pedal. Note gauge readings, then refer to Hydraulic Brake System/Specifications.
2. If left rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
Fig 44 Type 4 Proportioning Valve Pressure Gauge Test Connections. Left Wheel Malfunctions Less ABS:
a. Install one gauge of set tool No. C-4007A, or equivalent, between brake line from master cylinder secondary port and brake valve assembly.
b. Install gauge set tool No. C-4007A, or equivalent, as shown. A special adapter may be fabricated from a M12x1 tube nut, a short piece of brake tube and a 3/8 X 24 tube nut.
c. Bleed hose and gauge set.
d. 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. After installing a new combination valve, bleed hydraulic brake system as described under Hydraulic Brake System/Service and Repair/Brake System Bleed.
ANTI-LOCK BRAKE SYSTEM
On vehicles with Teves Mark IV ABS system refer to Anti-Lock Brake System for testing procedures.
All ABS components use an ISO type tubing flare. Ensure proper adapters with ISO type flare are used when installing test gauges.
1. Install one gauge of set tool No. C-700A, or equivalent, between hydraulic assembly and male end (inlet) of valve.
Fig 45 Type 4 Proportioning Valve Pressure Gauge Test Connections. With ABS:
2. Install second gauge of set tool No. C-700A, or equivalent, at female end (outlet) of valve.
3. While watching inlet and outlet pressure gauges, have an assistant depress the brake pedal. Note gauge readings, then refer to Hydraulic Brake System/Specifications.
4. If pressures are not within specifications replace proportioning valve.