Wheel lockup

power brakes. The big taurus is a vacuum amplifier that uses engine vacuum to 'pull on' the brakes to assist in the pedal. It has a mechaincal linkage to prevent all out loss of brakes due to vacuum loss or engine stopping. Think of the brake pedal rod pushing on a switch in the PB unit that bleeds vacuum into the side of the diaphragm that allows the diaphragm to move toward the M/C. That is your brake assist. if the vacuum is not present, the brake rod just pushes on a stop just past the point of activation and its a direct link to M/C piston. a brake that sinks the floor is usually an M/C