1965 4 wheel disc brakes

[zach_carver]

I wanna see if you guys have ever heard anything like the situation I am currently having. Ill try and sum it up. My truck has front and rear disc brakes with new master/booster and disc/disc prop valve. I have no brake fluid leaks! My truck has a perfect brake pedal until I hook up my vacuum to my brake booster. When I plug in my vacuum my pedal goes all the way to the floor with slight resistance. However Ive been driving the truck with it unhooked and it does fine. It all started after i replaced booster/master and installed rear disc. Anyone ever seen such??