disc brake kit issue, I've done 4 of em and I'm stumped on this one

a 10lb residual presure valve will not hold your brake shoes closer to the drums, the return springs have way way to much strength for that, there on there to keep the wheel cylinder rubbers against the walls of the cylinders so air can not leak past, if your master is lower than the wheel cylinders and air leaks past the rubbers then your brake fluid can run back and over flow the master, nice new wheel cylinders dont always alow air to leak past, i have had a few vehicles with the master lower than the wheel cylinders and no valves and no fluid leaks, the brakes work fine.

 

I'm just suggesting something the OP might want to check.Never said the 10 lb residual valve "holds the brake shoes closer to the drum". While the 10 lb valve is used to prevent air intrusion at the wheel cylinders, the 2 lb valve is used to prevent brake fluid from siphoning back to the master cylinder allowing the pads to retract from the rotor face. Could cause a braking issue. These valves are cheap insurance and pose no ill effects on the system even if not needed. Just because you got by without using them doesn't mean their invention was a waste of time.

 

Lot of good comments on this thread, hopefully it'll help people in the future.
For my issue, I think I got it fixed. Charlie, looks like you were right, I removed the sensor with the wire going to it on the proportioning valve, it had a spring loaded valve on it. I replaced that with just a pipe plug and rebled the front brakes.
That seemed to do the trick as the front brakes are working good now.
The rears still lock up so I may need to adjust the rear drums.
I'm not sure what that "sensor" is doing on the proportioning valve but by removing it I've got brakes. If anyone knows what it does, it's a factory 72 chevy valve.

 

The "mysterious" valve some refer to as a proportioning valve is in fact a combination or "combo" valve. The main bulk of the valve is a system pressure differential switch, which has a wire running from the "sensor" to a dash brake warning light. Also included is a fixed proportioning and/or front metering valve.
The "sensor" is a switch that is operates when a pri/sec system pressure differential of about 400 PSI occurs. This switch does not/cannot shut off pressure to either system. It CAN be defective and have leakage, although vary rare, which will allow the pri and sec systems to blend.
The metering, if equipped, has a small ****on that can be pushed in when bleeding, byp***ing the 100 PSI or so metering or "hold off" feature to the fronts.
You are much better off using an ADJUSTABLE prop valve instead of a factory fixed PV in a custom system, and definitely not one pulled from a '72 Chevy! (Brake parts 38 years old should stay in the junk yard!) And metering really should not be used in a custom system as it can cause aggressive rear braking.
Keep the system simple by using an adjustable PV, and use 10 lb residuals to all drum brakes (or the internally installed residuals in your master if equipped,) and 2 lb residuals to disc brakes ONLY IF the master is located below the calipers.

 

Yo V8 Bob, I'm in your camp with the "KISS" philosophy. I just had a discussion with a friend last night over this. People are always confusing the purposes of residual pressure valves, metering valves, combo valves and proportioning valves, especially RPV's and prop. valves. Isn't it arguable that you need a prop. valve in all systems, drum/drum, disc/drum, 4 wheel discs so that you can set up the system for the fronts to lock up before the rears? The only question in my mind right now that I have not resolved is the effect of big and little tire combinations. Seems that with smaller diameter and tread tires on the front, there is a bias for them to lock up first given all other things in the system being equal. Thoughts?

 

Here is a easy way to test the Proportioning valvo . Attach a test light to a hot wire and touch the conector on the valve if you get a light its stuck . To free the valve determin which side open bleeder screw if the fluid squirts out go to the other end open valae apply steady pressure to pedal till light gose out close bleeder and test