Hydraulic brake master cylinder with controlled center port valve gap and method of assembly

In automotive vehicle hydraulic brake systems, the brake mechanisms are actuated through a hydraulic circuit which includes a so-called master cylinder or actuator. The master cylinder, normally, includes two tandem arranged pistons which displace hydraulic fluid to respective brake circuits. Each piston is typically provided with a so-called center port or central compensation valve which operates to relieve pressure in the brake circuit when the brake pedal is released and to provide a supply of makeup fluid to the cylinder chambers for subsequent brake actuating cycles. A hydraulic brake master cylinder assembly includes a central or center port compensation valve mounted in respective brake actuator pistons and having a variable length stem which may be adjusted to predetermine the amount of valve travel between open and closed positions in response to actuation of the brake cylinder piston or pistons. The variable length stem includes a hub and a sleeve which is force fit over the hub and may be moved to set the length of the stem. The amount of gap or open position of the valve in the primary piston may be determined by installing the primary piston in the master cylinder, holding the piston in a fixed position and installing a seal retainer and washer for engaging the primary piston pin to move the pin to set the length of the valve stem.