Advance HCD400A Marine Gearbox The Advance 400 series marine gearbox has the functions of reverse, clutch, deceleration, and withstand propeller thrust. The HC400/HCD400 gearbox has a vertical off-center primary transmission structure, and the HCT400A/HCT400A/1 gearbox has a vertical off-center secondary transmission structure. This series of gearboxes have the characteristics of …