1972 C50 4 wheel drum low brake petal issue

[colgad]

I have a 1972 C50 that I shortened the frame and added a long bed to make a 2ton pickup. I had to replace most all of the brake lines along with all 8 of the wheel cylinders (there are two per backing plate).

The issue is that the petal goes right to the floor but you can pump it up and then the petal is hard and the truck stops great. If you wait 30 seconds and press the petal again it goes to the floor but will pump twice and be rock hard.

There is a power booster under the cab with another cylinder that looks like a master cylinder but with no reservoir.

I have bled the system to death using gravity or the normal two person method and the vacuum tool one man method. Starting passenger rear, driver rear, passenger front, driver front. The shoes are adjusted very tight to the drums.

I am out of ideas so any hints, comments, solutions are welcomed.

thanks so much
Dave