[jwheel55]

Possible master cylinder recuperating valve problem. Pressure built up when you apply the brakes is not bleeding down when you release the brake pedal. Open a bleed valve on one caliper and see if the fluid streams out under pressure. If it does it proves that the master cylinder is at fault. Also check that there is clearance between the push rod and piston when the brake is fully off.Some systems are adjustable. You can rebuild mastercylinders with new seals but this is a safety critical item so a new one is probably the best way to go. The vacuum diaphram doesn't usually cause this problem . Generally if it fails it reduces the power assistance making the pedal heavy in use. Hope you find this helpful , jonny.