I've been having brake problems lataly. It had the symptoms of a bad master cylinder, and since it was under warranty I went ahead and replaced it. After I installed it, and bled the system I have a real low pedal. Sometimes, while I'm bleeding the rear, the pedal firms up until I get to the front brakes, then after I crack the bleeder screw the first time the pedal goes down. I was reading some posts from awhile back and saw something about a button on the side of the proportioning valve. What is it for ? I can't say I've ever heard of having to push it while bleeding the brakes. Oh yeah, by the way I'm new to this site, so glad to be here.