On vehicles through 1980 equipped with front disc brakes, a metering valve is used. This valve is installed in the hydraulic line to the front brakes, and functions to delay pressure buildup to the front brakes on application. Its purpose is to reduce front brake pressure until rear brake pressure builds up adequately to overcome the rear brake shoe return springs. In this way disc brake pad lift is extended because it prevents the front disc brakes from carrying all or most of the braking load at low operating line pressures.
The metering valve can be checked very simply. With the car stopped, gently apply the brakes. At about 1 in. (25mm) of travel, a very small change in pedal effort (like a small bump) will be felt if the valve is operating properly. Metering valves are not serviceable and must be replaced if defective.