first thing make sure that pedal return spring is fully returning pedal ,and there is a small ammount of free play between pedal and footvalve/master cyl. if ok it could be brake hose failing internally.with wheel jacked up, if you repeatedly press brake pedal -does it bind?if it does [with it still binding] slacken bleed screw and check now for binding [dont forget to re tighten bleed screw ]if its free then it could be hose faulty.
k, August 2008