Ok changed my rear brake pads yesturday and made an attempt to so called bleed my brake lines of any air. So i unbolted the line and brake fluid poured out,a good amount and for some reason i also unbolted some valve next to it.I get everything back together and my brake fluid is ok bout halfway full and i pump the pedal a few times and now it goes almost to the floor.Test drove it and it still does it and even today,so it seems I may have did somethin this isnt safe cuz it takes me that much longer to stop or i need to brake early now.I took it to my mechanic yesturday and he said my master cylinder is shot and its a bit pricey to replace but how so when I didnt even touch it? any ideas on what to do?