Question: Will a '67 master work with a '64 power booster? I recently replaced all brake components & converted to a dual cylinder. Now, when I first start to drive the brake pedal compresses all the way to the floor. After just a minute of driving the brakes come back but still are not great. I now know there are different part numbers for boosters from '64-'66 and '67-'69. Do I need to replace this booster?

OK, no replies yet. Here's some more info on my situation. When I first start the car, no or little brakes. After a few minutes of driving/stopping they come back and are decent. It looke like I am losing line pressure after the car sits a while. I realize ther are residual valves in drum brake masters. That's how mine was ordered (in fact I have tried 2 '67 masters with the same results). What do I need to look into? Am I wrong stating that the '67 drum master has residual valves?