Patent ID: 6928813

Claim:
A master cylinder for use in a hydraulic brake system having a housing with an axial bore therein for receiving a primary piston and an operator actuable input member connected to said primary piston to reciprocate said primary piston within said bore, said primary piston being characterized by moving from a rest position in a direction to apply an increasing hydraulic braking force to effect a brake application; and in that said input member comprises an input piston and a variable length coupling interconnecting said input piston with primary piston, the length of said coupling being controlled by an axial location of the input piston within said bore such that said primary piston has an initial travel gain that accentuates the relative travel of said input piston and that after a predetermined travel said primary piston and said input piston move in unison, said input piston having a boss thereon that engages and moves along a helical outer groove located in said housing such that as opposition to the travel of said input piston increases, the travel gain of the primary piston decreases and the input piston travel increases during a brake application.