A master cylinder for use in a vehicle brake system having an operator brake pedal and individual wheel brake actuators (76, 78), comprising: a master cylinder housing; a first generally cylindrical bore in said housing; a first piston reciprocably disposed in said first bore defining in conjunction therewith a first variable volume chamber; characterized by a second generally cylindrical bore in said housing; a second piston reciprocably disposed in said second bore defining in conjunction therewith second and third variable volume chambers; said first and second chambers being connected to a reservoir to receive fluid and maintain the fluid level in the brake system at a desired level and being connected respectively to rear and front wheel brake actuators (76, 78) to supply pressurized fluid to effect a brake application; an electromechanical arrangement coupled to said first piston and operable in response to operator brake pedal force to urge said first piston in a direction to decrease said first chamber volume and apply fluid pressure to said rear wheel brake actuators; a mechanical coupling (44, 46) between said second piston and the operator brake pedal and operable in response to operator brake pedal force to urge said second piston in a direction to decrease said second chamber volume and apply fluid pressure to said front wheel brake actuators; and a fluid coupling conduit interconnecting said first and third chambers for applying fluid pressure from said first chamber to supplement operator brake pedal force urging said second piston in a direction to decrease said second chamber volume and apply fluid pressure to said front wheel brake actuators. a master cylinder housing; a first generally cylindrical bore in said housing; a first piston reciprocably disposed in said first bore defining in conjunction therewith a first variable volume chamber; characterized by a second generally cylindrical bore in said housing; a second piston reciprocably disposed in said second bore defining in conjunction therewith second and third variable volume chambers; said first and second chambers being connected to a reservoir to receive fluid and maintain the fluid level in the brake system at a desired level and being connected respectively to rear and front wheel brake actuators (76, 78) to supply pressurized fluid to effect a brake application; an electromechanical arrangement coupled to said first piston and operable in response to operator brake pedal force to urge said first piston in a direction to decrease said first chamber volume and apply fluid pressure to said rear wheel brake actuators; a mechanical coupling (44, 46) between said second piston and the operator brake pedal and operable in response to operator brake pedal force to urge said second piston in a direction to decrease said second chamber volume and apply fluid pressure to said front wheel brake actuators; and a fluid coupling conduit interconnecting said first and third chambers for applying fluid pressure from said first chamber to supplement operator brake pedal force urging said second piston in a direction to decrease said second chamber volume and apply fluid pressure to said front wheel brake actuators.