The gearbox of the Zodiac swimming pool cleaner is integral part and replacement part of steering system. The Zodiac MX8 pool cleaner functions with two gearboxes, marked A and B. Gears inside the gearbox ensure correct directional change-over and steering of the machine. Zodiac Gearbox A and Gearbox B What's in the box 1x Gearbox Side A, 1x Gearbox Side B