Gearbox comprising a system of variation of the pitch of blades of a rotor, said system of variation of pitch comprising: • a rotating tube of variation of pitch rotationally mobile around an axis OZ and translationally mobile along the axis OZ, said rotating tube of variation of pitch being rotationally integral with a rotor shaft with respect to a fixed chassis of said gearbox, • a rod of variation of pitch translationally mobile along said axis OZ with respect to said fixed chassis of said gearbox, and • a bearing of variation of pitch comprising an inside ring, an outside ring and a plurality of rolling elements interposed between said inside ring and said outside ring, said bearing of variation of pitch cooperating both with said rod of variation of pitch and said rotating tube of variation of pitch, said bearing of variation of pitch being configured to transmit a translation movement along said axis OZ of said rod of variation of pitch to said rotating tube of variation of pitch, said rod of variation of pitch comprising a first free end integral with said outside ring of said bearing of variation of pitch, said rotating tube of variation of pitch comprising a second free end integral with said inside ring of said bearing of variation of pitch and said system of variation of pitch comprising a lubrication circuit piping a lubrication fluid at said bearing of variation of pitch, characterised in that said first free end comprises an external protuberance, an internal cavity and at least one pipe extending radially between said external protuberance and said internal cavity, said at least one pipe being configured so that said lubrication circuit pipes by gravity said lubrication fluid from said external protuberance to said internal cavity. • a rotating tube of variation of pitch rotationally mobile around an axis OZ and translationally mobile along the axis OZ, said rotating tube of variation of pitch being rotationally integral with a rotor shaft with respect to a fixed chassis of said gearbox, • a rod of variation of pitch translationally mobile along said axis OZ with respect to said fixed chassis of said gearbox, and • a bearing of variation of pitch comprising an inside ring, an outside ring and a plurality of rolling elements interposed between said inside ring and said outside ring, said bearing of variation of pitch cooperating both with said rod of variation of pitch and said rotating tube of variation of pitch, said bearing of variation of pitch being configured to transmit a translation movement along said axis OZ of said rod of variation of pitch to said rotating tube of variation of pitch, said rod of variation of pitch comprising a first free end integral with said outside ring of said bearing of variation of pitch, said rotating tube of variation of pitch comprising a second free end integral with said inside ring of said bearing of variation of pitch and said system of variation of pitch comprising a lubrication circuit piping a lubrication fluid at said bearing of variation of pitch, characterised in that said first free end comprises an external protuberance, an internal cavity and at least one pipe extending radially between said external protuberance and said internal cavity, said at least one pipe being configured so that said lubrication circuit pipes by gravity said lubrication fluid from said external protuberance to said internal cavity.