A brake system includes a master cylinder generating pressure at first and second MC outputs for actuating first and second pairs of wheel brakes. A secondary brake module is configured to provide fluid at first and second PTU outputs for actuating the wheel brakes. The secondary brake module includes an electric motor configured to selectively pressurize the hydraulic fluid by transmitting rotary motion to at least two pump pistons. A pump inlet attenuator is interposed hydraulically between a reservoir and the pump pistons and in direct fluid connection with the reservoir via a single return line. An electronic control unit controls at least one of the secondary brake module and the master cylinder responsive to a brake pressure signal. The pump inlet attenuator regulates pressure in the single return line to reduce pressure fluctuations at an inlet side of each pump piston via solely mechanical pressure attenuation.

A brake system includes a motor-driven master cylinder for generating brake actuating pressure at first and second MC outputs for hydraulically actuating pairs of wheel brakes. A secondary brake module is configured for selectively providing pressurized hydraulic fluid at first and second PTU outputs for actuating the first and second pairs of wheel brakes. A low pressure accumulator is interposed hydraulically between the first and second pairs of wheel brakes. The low pressure accumulator is in indirect fluid communication with the reservoir via the first and second MC outputs and the master cylinder. The low pressure accumulator at least partially provides slip control to the wheel brakes in coordination with the secondary brake module when the brake system is in the normal non-failure braking mode.

A tandem power transmission unit includes a ball screw and a ball nut selectively driven by the ball screw for longitudinal motion relative thereto. A primary piston is operatively coupled to the ball nut. A secondary piston is operatively coupled to the primary piston. A primary chamber is configured to contain hydraulic fluid and is selectively pressurized by reciprocal motion of the primary piston. A secondary chamber is configured to contain hydraulic fluid and is selectively pressurized by reciprocal motion of the secondary piston driven indirectly by longitudinal motion of the ball nut. A first output channel selectively places the primary chamber in fluid communication with at least one component of a brake system for provision of pressurized hydraulic fluid thereto. A second output channel selectively places the secondary chamber in fluid communication with at least one component of a brake system for provision of pressurized hydraulic fluid thereto.