I just blew out my third wheel cylinder on the drivers rear last night. This has all happened within the last 2 days after thorough examination of the brake system I think the problem lies in the proportioning valve giving too much pressure to the rear brakes. I noticed that the button on the end of the valve was stuck and not moving. Is the default position for this button in or out? I have heard that you need to hold the button in while bleeding the brakes and I did not do this, but I have before without any problems. Could the valve come open while bleeding the brakes? Also could pumping the pedal with the key off instead of on have anything to do with the problem I was having? This all started when I noticed that the brake line coming from the prop valve to the right front brake was leaking so I replaced it. I am out of ideas and tired of changing wheel cylinders and adding brake fluid to get the car home. Any help greatly appreciated.