"No feedback brakes" go from nothing to full lock

The power brakes on my 74 Duster feel like that, at low speed. The fronts.... Like Nothing, then, at the end they grab. Could be the .484 cam, as it's butt as noted when rolling... but I ain't panic stopped it. New pb, and master. Gonna ditch em and go manual...lots a great Guys and Gals here, and some of the most Experienced minds. This is the place. Please post your results for us? Hope Ya get it fixed!