Update...

Step 1 - tightened up the rear shoes. No difference.

Step 2 - bled the master cylinder, minor improvement.

Step 3- bled the fittings on the proportioning valve, no change.

Step 4 - got a pretty good vacuum bleeding kit and bled everything twice again with that, no change

Step 5 - adjusted the pushrod on the pedal/master. That seemed to help a tiny bit.

I have a slight pedal now, and it gets better if I pump it 10 times but it bleeds off when I release and push it again.

Continuing to diagnose...


1953 GMC 1-Ton Pickup with 350 and 700R4