Abstract: A power steering casing capable of operating in a power-assist mode and also capable of operating in a strictly mechanical mode. The power steering casing includes an inner cylinder where there is disposed a piston affixed to an end of a rack bar. The rack bar projects outside of the steering casing for connection to steering linkage of the vehicle. The steering casing is in communication with a valve which controls the passage of a power-assistance fluid in response to turning of a steering wheel. The valve comprises a jacket and a valvular nucleus. The valvular nucleus is connected to the vehicle's steering column, while the jacket is connected to a bushing on the pinion. The pinion meshes with the rack bar. The bushing is connected, via an anchorage piece and pin, to a torque bar that coaxially extend through the valvular nucleus from the bushing to the steering column.