Brakes not working

[Heath Pendlay]

1960 comanche 250.....
Just had the master cylinders rebuilt last week. Everything went back together good and pumped the system full of fluid from the bottom up. Initial test of brakes while it was in the shop went well, but when I went to taxi back to my hanger, the brakes would only work when you first push on them. After that, they will both go to the floor. They will not work again until you let off 100% and wait 2 - 3 seconds. The next time you use them they work excellent until you start feathering them at all. After that they both go to the floor. I drained all the fluid and let it set for an hour and then refilled the system by pumping up through the bleeder on the caliper. When I took it out for a test it does the same thing.
Basically, if you need to apply brakes, they work if you push hard and keep constant pressure on them. If you ease up on the foot pressure or let off a little, the peddle will go to the floor and there is no way to stop or slow down until you let off completely for a few seconds (to let something reset?) and then re apply pressure.
Has anyone ever heard of such a thing.
Heath-7139P

[Timothy Poole]

[JIMICS2452]

I bleed brakes from the bottom using the Brake Bleeding Pressure Pot for Aircraft Tool Supply. It is easy to use and can provide enough pressure and fluid flow to force all bubbles, especially the ones in the master cylinder/parking brake out of the system.

[Timothy Poole]

[JIMICS2452]

I have to pump up a lot of pressure for my Comanche.