All transmissions have two main parts: the gearbox as well as the torque converter (or in the case of the handbook transmission, a clutch). The gearbox is responsible for in fact shifting the gears, although the torque converter really helps to transfer the power in the motor towards the gearbox. https://ericktndsh.idblogmaker.com/33228883/the-2-minute-rule-for-filter-gearbox