Without Antilock Brakes

Fig. 35 Proportioning Valve Pressure Test Connections:

Fig. 36 Proportioning Valve Pressure Test Connections:

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.
1. If right rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
a. Install one gauge of set No. C-4007A or equivalent between brake line from master cylinder secondary port and brake valve assembly.
b. Install second gauge of set 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 Controls Specifications" chart.
2. If left rear wheel slides first, leave front brakes connected to valve, then proceed as follows:
a. Install one gauge of set No. C-4007A or equivalent between brake line from master cylinder secondary port and brake valve assembly.
b. Install gauge set 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.
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 Controls Specifications" chart.
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 Bleeding & Flushing."