I had a hard brake pedal on my KP61 when i bought it.
I replaced the wheel cylinders, rotors, calipers, drums, lines and master and booster(everything) and at first all was well. It felt good, But after about 20 miles the brakes would start dragging. Now the pedal is rock hard again. The brakes don't appear to be dragging. But I'm affraid to drive it much because of how hard it is to stop.
Is there a proportional valve and what could be going on? The manifold vacuum seems to be strong BTW.