[buddy_1]

Did both sides free up by opening one bleeder? Or, did each one free up when you opened its individual bleeder? Yes it is possible to be a master cylinder problem. Pump the brake until the tires lock up then loosen the line at the master cylinder to see if they free up. These old trucks are notorious for hose concerns. Pump the brake until the tires lock up then loosen the line fitting going to the frame end of the caliper hose. See if it frees up, if not, the hose is collapsed internally.