A mechanism (106) for selecting one of a first gear (102) and a second gear (104) for driving an automatic swimming pool cleaner (10) includes a bi-stable oscillating gear change assembly (100). The assembly is moveable between a first position wherein the first gear is engaged and a second position wherein the second gear is engaged. A first magnet (142) is carried by the assembly. A second magnet (138, 140) is carried externally of the assembly on the cleaner body (18). A cam arrangement (152, 160) initiates movement of the assembly (100) from one of the first and second positions to enable mutually repelling forces between like poles of the first and second magnets (142, 138, 140) to cause the assembly to settle in another of the first position and the second positions, thereby to change between the first and second gears quickly and cleanly.