Manual transmission is clearly the best mode of transferring engine power to the wheels. It’s the simplest design, most engaging, easiest to maintain, and most efficient. This explains why the #SaveTheManuals movement is so important to many enthusiasts and consumers alike. Soon enough we may see a #SaveTheTorqueConverter movement with the advent of automated manuals like dual-clutch transmissions, that offer lightning quick automated shifts without the poor efficiency found in a fluid-coupling.
But before we ignore and forget the transmission that has powered hundreds of millions of cars, and the one that’s still being widely used today, we should examine how it functions closely. And nothing does that better other than a classic old video from the Department of Defense, explaining the inner workings of the transmission with see-thru models and cutaways.
To put it simply, the torque converter is a fluid pump filled with oil. The side of the torque converter attached to the engine has stationary vanes that, when the engine is turned on, rotates with the driveshaft and forces the oil to move. The centrifugal forces applied to the oil forces it to move radially outward and back into the transmission side of the torque converter, called the turbine. As the engine side spins more quickly, the oil moves more rapidly and imparts greater and greater forces on the transmission side to make it rotate.
The nature of the torque converter does not allow the engine to stall at a stop. All of the extra energy imparted on the fluid gets dissipated in the form of heat, as it is not large enough to overcome the transmission load. This also explains why automatic/torque converter transmissions are less energy efficient, which can be seen in vehicle’s mileage ratings. Some of that horsepower is necessary to rotate additional parts, primarily the oil itself, in order to achieve the same effect of a third pedal.