The brake master cylinder is the heart of your braking system, pumping fluid at high pressure to all the wheel cylinders. Even if it's not leaking externally, a faulty internal bore may allow fluid past the seals causing a loss of efficiency and excessive pedal travel. Early Minors with 7" front drums used a 7/8" bore master cylinder CBS133. In 1964 the brake drum increased to 8" with a 13/16" master CBS144. Because changing the cylinder is a job you don't want to do twice, we recommend replacing rather than rebuilding brake cylinders when possible. CBS144 now replaces the obsolete CBS133. This is the original AP Lockheed type. For the aftermarket version, see part CBS144A.