The inner workings of a transmission housing include gears, hydraulics, drive and input shafts, electronic components, clutches and various seals and gaskets. Particular arrangements or components may vary slightly from vehicle to vehicle, but the overall function remains constant.
Automatic transmissions are intensely complicated, using computer-controlled shift points to transition the vehicle between gears. The transmission is physically operated by transmission fluid, delivered in a variety of methods, under pressure within the housing. Manual transmission vehicles operate with an input shaft attached to a layshaft that moves gears at a fixed ration. The layshaft is then connected to an output shaft, which is attached to the drive line or differential to generate torque for forward motion.