67 C10 Manual Drum/Drum Brake Help

[A.Bursell]

Hello,

One of my projects on my 67 is getting the brakes in order so I can drive it. I did drive it home and I had about a 50% chance of getting brakes when I stepped on the pedal. I figured it was leaking wheel cylinders (which they all were). They are manual drum/drum brakes. I just replaced the ORIGINAL parts on the truck, and yes they were very worn out.

Cut drums (also drilled the rivets from the hubs), replaced and repacked bearings, new shoes and hardware, cleaned anything reused, new wheel cylinders, new soft lines, flushed brake fluid (which came out looking like MUD but is clean after 5 bottles of fluid) starting with LR and working my way closest using speedbleeders I decided to try.

I thought this would do it, but took the truck out to get the brakes adjusted and it is stopping much better, but it seems I still have similar symptoms. Sometimes I get good brakes, sometimes the pedal will go to the floor when I stop.

The only things left in the system are the hard lines and the master cylinder and what I thought was the proportioning valve. I don't believe the hard lines have a problem or I would see leaks someplace after putting so much fluid through the system. That leaves the master cylinder and proportioning valve. I have been searching around and it seems that the "valve" might be just a switch in my drum/drum application and not have any impact on the fluid.

Long story short, my questions are:

1) Does this sound like a master cylinder problem? (I hope so, since it's the only thing left!)
2) Is the "proportioning valve" just a switch in the drum/drum application -- can it go bad and cause me braking problems?
3) Is there anything I am overlooking?

Help and thanks,

Adam