AP Racing Short Forged Master Cylinder

A hydraulic handbrake acts directly on the rear calipers. It locks the axle without going through the cables, providing clean, repeatable lock-up — something the original cable can no longer do once the car gains weight or grip.

The master cylinder bore size is not a minor detail. The smaller it is, the faster the pressure rises for the same lever effort, but the longer the travel becomes. A 0.75" bore suits most standard rear calipers; a larger bore is reserved for calipers with large pistons.