Ok, guys, thank you for your answers. Let me add few things: there in no leaking fluid in the master cylinder, that is still full. Second the vacuum hose going to the booster is brand new, and with the engine off the brake pedal does not move at all or or at least maybe 1/4 inch. The master cylinder was rebuilt many years ago but never installed until few months ago. So was the booster. Since I started driving (3 months or so) the brakes were very sensitive, to the point I had trouble modulating the pedal without locking the breaks every time, and then....and I repeat, when I start the engine the brake pedal can be pushed all the way to the floor, but no brakes. That' s about it, at least for now.