The size, weight, and cost of a full-traction differential are significantly reduced by the synergism of several interrelated design features of a cartridge-like gear complex: (1) Each combination gear has only a shallow journal hole in each end of an otherwise solid gear body, being supported on mating hubs fixed to mounting plates slipped into a one-piece differential housing. (2) The solid worm-wheel portion of the combination gears has a deeper hour-glass shape. (3) Mating worm/worm-wheel teeth have a broad 'supra-enveloping' contact pattern on only the drive side of the mesh. (4) The side-gear worms have closed-end teeth. (5) Both diameter and axial length of the side-gear worms are reduced by a special cutting process. The efficiency of the differential is increased by a thrust plate supported in the mounting plates and positioned between inner ends of the side-gear worms.