I posted earlier on some reasons why the brake pedal sinks; my '63 has a front brake disc kit in it with booster converting to power brakes. Had to re-do the brake pedal as it was real high cutting down the push rod and installing a better eyebolt. Pedal sinks when starting the car until pumping a few times but having to put foot in back of pedal to bring it up. The brakes though are not engaged when this happens. After some driving time same thing happens on occasion. Installed an auxiliary reservoir I got from Jegs. Same friggin problem. Even put in a return spring and same thing still happens. A heavier spring is likely needed; but chit shouldn't need one to begin with. Have ample vacuum and booster holds pressure hearing a quick whoosh when disconnecting the connection. If brakes would lock when this happens that's one deal; but loose the pedal almost to floor but can still engage brakes. Prop valve seems adjusted fine...nice braking action, no leaks anywhere. Any other thoughts on the fix? Thanks