Did you ever resolve the problem? Had/Have same issue on 67. Ended up replacing most components, seemed to start working better for a couple drives then came back. Seems to happen if the car sits for a week or two without driving, but no specific remedy determined. Haven't had my car out at all this summer because unable to resolve again. Now issue on both front wheels. I just barley touch the pedal it locks up hard. I've had short rods, log rods, new stainless lines, calipers, master cylinder, booster, distribution block etc.. Feel like I should put wing nuts on my wheels I've had them on/off so many times. No luck and pissed.