Brake pedal all the way to floor, but not loosing fluid?

Sudden onset of pedal all way to floor. Only problem was intermittent humming or howling coming from rear drum. Did front disc brake a month ago, and left too much fluid in the reservoir; could that have made them fail. Tiny bit of brake at the bottom of pedal stroke, and alittle more if pump brake. Would a vacuum leak do this? 2002 Ford Winstar.