GM Corvette 1963-1982 Repair Guide

Combination Valve


The combination valve, found on 1978-82 vehicles, is mounted on the frame and is connected to the hydraulic lines from the master cylinder. The proportioning section of the combination valve proportions outlet pressure to the rear brakes after a predetermined rear input pressure has been reached. This is done to prevent rear wheel lock-up. The valve is designed to have a bypass feature which assures full system pressure to the rear brakes if the front brake system fails and full system pressure to the front brakes if the rear brake system fails.

The warning switch is designed to constantly compare front and rear brake pressure from the master cylinder and turn on the light on the dash in case of front or rear system failure. The warning light switch portion of the combination valve is not serviceable. If the switch is found defective the combination valve must be replaced.


See Figure 1

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Fig. Fig. 1: Combination valve location and mounting

  1. Disconnect the hydraulic lines at the combination valve. Plug the lines to prevent loss of fluid and to protect the system from dirt.
  3. Disconnect the valve switch wire terminal and remove the combination valve.
  5. To install reverse the removal procedure and bleed the brake system.


  1. Raise and safely support the vehicle.
  3. Attach a bleeder hose to a rear brake bleed screw and immerse the other end of the hose in a container partially filled with clean brake fluid. Make sure the master cylinder reservoirs are filled.
  5. Turn the ignition switch to ON and open the bleeder screw while a helper applies moderate pressure to the brake pedal. The warning lamp should light. Before the helper releases the brake pedal, close the bleeder screw. Press down on the brake pedal and the light should go out.
  7. Attach the bleeder hose to the front brake bleeder and repeat Step 3. Turn the ignition switch OFF.
  9. If the warning lamp does not light during Steps 3 and 4 but does light when a jumper is connected to ground, the warning light switch portion of the combination valve is defective and the combination valve must be replaced.