I have a disc/drum set up on my 70 cutlass, what does the metering valve do? Does it keep the disc up front from locking up? or does it retard the braking effort on the rear brakes? The plunger on the rear of mine barely seems to move and gets stuck (when bleeding) can this be cause for a low brake pedal and poor braking?

 

I don't know the exact amount, but the front disc brakes get more fluid than the rear. I believe that's the primary function of the valve. Can you provide more details on the plunger your describing? I've never seen one of these valves fail, usually it's air in the lines that I've had cause poor braking. Did you recently work on the system? If you replaced the master cylinder did you bench bleed it before installing? John

 

The valve holds off the hydraulic pressure to the front disc brakes until 130 PSI has been reached in the rest of the system.
The button you keep depressed bypasses the metering section of the valve to allow even pressure to the front and rear brakes when bleeding.
My Vista's valve started leaking around the button so I replaced it, the button got stuck sometimes too.
There are several things that can cause a low pedal and hard braking from air in the lines to an improperly adjusted MC push rod, but if you think everything else checks out the manual says that a faulty metering valve can cause excessive brake pedal travel.
Inline Tube sells the brass repos if you need one.
Supercars Unlimited has rebuilt originals available on an exchange/ special order basis.

 

I replaced the MC thinking it was bad, I did bench bleed it. The system sat for a couple of months will doing engine bay work and rebuilding the engine . I have bled the whole system after putting it back together. But it seems that the rubber covered button behind the metering valve gets stuck (when bleeding) and the rubber cover is also severely cracked and ripped. Going to replace the brake lines next, bleed it of course to see what happens. There is also a little slack I can take up on the rear drums, then go from there. But I m guessing the air might be getting into the system through the rubber button cover (looks like a priming button on a lawnmower). Do you think that there might be something with the calipers?