A helical planetary gear assembly includes a ball bearing secured to a housing, a carrier sleeve coupled with an inner race of the ball bearing and being axially restrained by engagement therewith, an input shaft supported by the ball bearing through the carrier sleeve, an output shaft arranged coaxially with the input shaft for rotation relative thereto, a sun gear secured to the input shaft for rotation therewith, a ring gear secured to an internal wall of the housing, a planet carrier arranged between the sun and ring gears, and a plurality of planet gears rotatably supported by the planet carrier and being in meshing engagement with the sun and ring gears, the gears each being in the form of a helical gear. The planet carrier includes a body member secured to the carrier sleeve for rotation therewith, and the input shaft is axially restrained by opposite ends of the carrier sleeve through a pair of axially spaced thrust bearings.