Replaced that line, and bled them, got lots of brakes. Parenthetically, that is a weird braking system. Two lines to the back, that ran into one block, then a rubber hose down to the axle, and the split to the rear wheels.
We think the rubber line was collapsing, blocking flow to the wheels. Finally it leaked and we changed it out, but that took a real long time.
Life is harder when you're dumb.