1954 Cadillac - GM Heritage Center

The Cadillac Power Brake is a vacuum-power unit connected
to the hydraulic brake system and to the intake manifold.
A piston is enclosed in the unit. With vacuum on either side
of the piston, the forces are balanced and the piston does
not move. But, when pressure is applied to the brake pedal,
air enters one-half of the unit and the difference in pressure
actuates the piston. The force produced by the piston assists
in the braking. When the brake is released, vacuum again
enters both sides of the piston, and a spring returns the
piston to released position. Should the power unit be accidentally
damaged, the brakes operate as usual, but with no
power assistance. Thus, the unit is completely safe.
A Brake line pressure outlet.
B Brake line pressure inlet.
C Vacuum line from manifold.