Hydraulic brake unit for vehicles including a fluid level sensor

The assembly (14) has a master cylinder (16) connected to an electric brake assistance servomotor (15) by an assistance piston (23) that is actuated by an electric motor (22) of the servomotor. A hydraulic fluid reservoir (17) is mounted on the cylinder. The reservoir communicates with a master cylinder chamber for supplying hydraulic fluid to the cylinder. A hydraulic fluid level sensor (25) is situated in a reservoir wall for controlling the level of hydraulic fluid in the reservoir. The sensor is connected from the reservoir towards a controller (19) of the servomotor by a cable (26). The hydraulic fluid level sensor is a REED switch sensor or a Hall-effect sensor or magnetic proximity sensor.