Patent ID: 6935110

Claim:
A tandem master cylinder wherein fluid under pressure is supplied to a primary outlet port from a primary pressure space in a bore between a positively actuated main piston and a secondary piston, and to a secondary outlet port from a secondary pressure space between said secondary piston and an end of a housing closing said bore, a position of said main piston with respect to the secondary piston being determined by a length in a released position of a return spring which acts between said two pistons, said return spring being caged between said main piston and a sleeve in abutment with said secondary piston and which is coupled to said main piston through an axially extending headed stem to determine a defined position, further in which distal end of said stem is of a reduced diameter to define a step in diameter and a shoulder at said step in diameter defines a cutting edge, insertion of said stem into a bore in said main piston of a diameter not less of that of said distal end causing said cutting edge to cut into material of said main piston until said defined position is reached and to key said stem to said main piston at that position against withdrawal of said stem from said main piston.