An add-on brake system configured for clamping a wheel disc of a vehicle, the add-on brake system comprising: - a housing accommodating a direct-drive linear actuator comprising: ∘ an electric motor comprising a rotor and a stator ∘ a nut arrangement fixedly and directly coupled to the rotor and configured for revolving therewith; ∘ a linear threaded plunger associated with the nut arrangement for being driven thereby in a linear direction upon the revolution of the latter, said plunger having a first end (21 I) linearly protruding from one end of the nut arrangement and a second end linearly protruding from an opposite end of the nut arrangement; - at least one inboard brake pad fixedly coupled to the housing; - at least one outboard brake pad associated with the second end of the linear threaded plunger, oriented transverse to the linear threaded plunger and configured for being driven thereby in the linear direction; said linear threaded plunger being configured for assuming an initial unclamped position in which the second end protrudes to a first extent n 1 from the other end of the nut arrangement, yielding a first spacing S 1 between the inboard and outboard brake pads (50, 60), and a final clamped position in which the second end protrudes to a second extent n 2 > n 1 from the other end of the nut arrangement, yielding a second spacing S 2 < S 1 between the inboard and outboard brake pads (50, 60), allowing clamping the wheel disc; wherein the linear threaded plunger comprises a restricting member, configured for preventing the plunger from rotating about its axis, whereby revolution of the nut arrangement about the linear threaded plunger restricts the displacement of the linear threaded plunger only to the linear direction, wherein the restricting member is associated with the housing in a manner preventing revolution of the linear threaded plunger, characterized in that the restricting member is a pin having a first end associated with the linear threaded plunger and a second end received within a channel formed in the housing and preventing revolution of the pin, and wherein the channel extends in the longitudinal direction, wherein, when said plunger linear threaded displaces in the linear direction, the pin travels together with the linear threaded plunger, its second end sliding within the channel of the housing. - a housing accommodating a direct-drive linear actuator comprising: ∘ an electric motor comprising a rotor and a stator ∘ a nut arrangement fixedly and directly coupled to the rotor and configured for revolving therewith; ∘ a linear threaded plunger associated with the nut arrangement for being driven thereby in a linear direction upon the revolution of the latter, said plunger having a first end (21 I) linearly protruding from one end of the nut arrangement and a second end linearly protruding from an opposite end of the nut arrangement; ∘ an electric motor comprising a rotor and a stator ∘ a nut arrangement fixedly and directly coupled to the rotor and configured for revolving therewith; ∘ a linear threaded plunger associated with the nut arrangement for being driven thereby in a linear direction upon the revolution of the latter, said plunger having a first end (21 I) linearly protruding from one end of the nut arrangement and a second end linearly protruding from an opposite end of the nut arrangement; - at least one inboard brake pad fixedly coupled to the housing; - at least one outboard brake pad associated with the second end of the linear threaded plunger, oriented transverse to the linear threaded plunger and configured for being driven thereby in the linear direction;