Abstract: A differential gear mechanism (11) and improved axle shaft (53) retention arrangement for the axle shaft. The mechanism includes a side gear (27) defining first internal splines, a coupling (35) defining second internal splines (35S), and a rotor (49) of a gerotor pump defining third internal splines (49S). The axle shaft includes external splines (55), an annular groove (57), and a collapsible and expandable retention ring (59) within the groove. The assembly operator aligns the external splines with the third internal splines (49S), then with the second internal splines (35S), and finally, with the first internal splines (27S), before exerting force (“F” in FIG. 3) on the axle shaft to collapse the retention ring by passing it through the third internal splines (49S) until the ring can expand (FIG. 4). The axle shaft is retained as the retention ring engages an inboard end (69) of the third internal splines.