Spongy brakes, 914-4 brakes won't firm up??! Options

[Gearren]

I've had it! I have done everything to the brakes on my car, and I can't seem to get them to stop the car with authority. Best I get is a reluctant coast to a stop. Hardly suitable for street use! I have owned the 73 2.0 since new, and have kept it in the garage since 85. Brakes have always been weak, so as I starterd on the quest to revive the car, the brakes were top on the list. I have rebuilt both front and rear calipers, turned the rotors, new pads, new M/C (17mm), bled the m/c, bled the prop valve, and bled the system at least 10 times! I still have weak/spongy brakes! I want to keep the car stock, however I am tempted to remove the prop valve to see if it is the culprit. Any ideas or suggestions would be appreciated??

[davep]

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I use new rubber lines, a 19mm master, and a tight venting clearance. I really like the old fashioned 2 person bleeding system best.
One thing that could be affecting you is wobble in the turned rotors. One way to test this is to pump up the brakes while at rest. If it feels hard the second or third time you put your foot on the brake, then the system should have been bled properly. If it feels soft, then either the lines have some bubbles or the rubber lines are flexing. If the brakes feel hard while stationary, but get really soft while rolling, then the rotors may be pushing the pads back too far, thus requiring pumping of the brakes to get the pads to work. Rear rotors are more prone to wobble due to being mounted on the hub. If the mating surfaces are not perfectly clean and smooth you will have excessive wobble, and thus excessive venting clearance. Setting the venting clearance manually will not correct the clearance generated by wobble. Note that the design of the system deliberately uses wobble to generate venting clearance; that is how the front is set up. Yes, the piston seal O-rings also contribute to this, but the amount of wobble is the maximizing factor.