treadlevac woes..

I plugged with an inverted flare plug. There are new copper compression washers on each side of the brass block also

 

One less thing. Now off to the brake lines.

 

I see the pedal is rock hard with the ports blocked, which is good. Vacuum bleed the lines one by one and you should be okay.

 

ok good. now adjust the brakes up locked, go as tight as you can. and see if the pedal is hard if it is, the problem is shoe fit/adjustment.

 

That bleeder is below the output fitting so some air may remain in the system anyway.
No experience with that exact setup, but Hydrovac's on big trucks have bleeders on them and many little passages to catch air. The only way to get them to work is a pressure bleeder and LOTS of brake fluid. I mean like quarts! If there is a speck of air in them they will drive you nuts.
I mentioned on another thread that some modern fluids aren't compatible with old-manufacture brake rubbers. They swell up slightly and don't work right. I had to get the "old guy" at the parts store to find one that worked. Then I rebuilt the whole system again.

 

I agree on the possibility that there might be trapped air in that bleed valve cavity. Plugging the outlet as you did and bleeding thru the bleed valve may get you somewhere, but since you have a firm pedal with the MC plugged would tend to eliminate a pocket of air at the bleed valve.


Also on the subject of fluid vs rubber, yes that is true, especially on English cars of old. They used natural rubber and most fluids are for synthetic rubber and will cause natural rubber to do weird things. In the case of the treadlevac and wheel cylinders this should not be the case.