get you some line clamps and clamp off each line one at a time starting at the rear. if the pedal gets hard like its supposed to like your talking about, then there is a prob some were in the rear. if not put it on the RF wheel. same thing. if not put it on the LF(all 3 hoses should be line clamped now). if the pedal is hard, master is good but if it still goes down its the master or prop. valve. are you using a new or used prop vavle?