[1969 Stang]

First my brakes a sort of new...front disc rear drum...now the brake pedal has to be almost all the way down for me to stop at a stop sign or stop light...and so on...now when I push the pedal even a little bit I hear a hisss sound...kind of like when you let out the air in a coke bottle slow...what could be the problem...Its scary to drive my car...and now its going to rain...if no one knows just pray...thanks.