72 Duster Resurrection

I called and talked to inline tube and did some internet research. The combination valve (distribution plus prop for rear brakes) is the correct one for a 74 disk drum setup.

Every single inch of brake line is brand new(inline tube pre-bent hardlines and new hoses all around)

Both back drum cylinders are new

Both from disk calipers are new

New master cylinder

I disconnected the line going from the combo valve to the rear and blew some air threw it and got air out each open rear bleeder separately so the lines are all clear (again, they're all new).

I have also spent several hours with a mighty vac and eventually a pressure bleeder(pumps fluid down through the system from the maser cyl). Many qts of brake fluid have come out each bleeder(fronts and rears).

And still I have a spongy brake that acts like this:

First pump, pedal goes to floor
Second pump, pedal goes halfway down and stops pretty firmly

I also verified with someone holding the pedal after the second pump that the front wheels are locked but the backs are free to spin.

Also a test light on the warning switch lights up when connected to batt positive and the switch post on the combo valve.

So I think my combo valve is off center but I can not get it to re-center. I opened both front bleeders and pressed brake pedal. Brake warning light still on. I then removed the lines going from combo valve to both front wheels and pressed brake pedal (even stomped it). Warning light still on.

Im confident that I have all the air purged from my new brake system but I. just. can. not. get my combo valve to deliver fluid to the rear. Any yes, this is the second new combo valve I have tried.

I think my master cylinder has a built in residual pressure valve on the rear brake output but I dont think that should matter..

Anyone have thoughts?