Over the course of about a week the brakes on my 72 K5 seemed to be getting worse. I have power brakes (disks up front, drums in rear). The peddle has become very dead (hard). I checked all of the pads, bled all of the lines several times over, bench bled the master cylinder, but still have the same problem. Could this be a problem with the booster? When bleeding the brakes, I made sure to hold in the metering pin on the combination valve, but the pin did not seem to give any resistance. I expected it to feel "spring loaded". Could there be a problem with the combination valve? Any advice is appreciated.