I have go, but can't figure out whoa.
 

I have a 1971 Beetle that sat for the last 20 years and I got it running and replaced everything brake related...master cyl, lines, wheel cyls, hardware, and shoes. My question is, I bench blead the master cyl and installed it, blead all four wheels, and I can pump up the brakes and they hold good pressure...when I let off for a second and reapply the brake pedal, it goes to the floor...??? I rechecked all four wheels for lining adjustment and have absolutely no leaks...I even changed master cyl twice thinking I could have got a bad one??? I am lost. PLEASE HELP. I am new to VW Beetles...

RE: I have go, but can't figure out whoa.
 

Check the adjustment on the pedal to the master cyl, That would
be the rod connected to the brake pedal and slides into the master
cyl. With your hand, place a finger on the pedal and ease down
lightly, see if you feel when the plunger strikes the master cyl, you
should have any where from 1/16 inch to no more than 1/4 inch
movement. If you have more, then adjust the rod to the above specs. if you don't have any, then adust to the above specs.
The brake adjustment at the wheels will have two star adjusters
at each wheel, adjust each one untill the wheel is locked by the
brakes, then unadjust about three or four clicks , do this on all
four wheels and you will have eight adjustments with all the wheels.
At this point you may have to rebleed the system, and make
sure the fluid reservoir is in place and not leaking down the side
of the master cyl.