Torque Converter
A fluid coupling device in automatic transmission vehicles that transfers rotational power from the engine to the transmission while allowing the engine to remain running when stationary.
The torque converter is the automatic transmission's equivalent of a manual clutch. It is a large, doughnut-shaped metal component positioned between the engine's flexplate and the transmission. Inside the converter, a pump (driven by the engine) forces automatic transmission fluid into a turbine (connected to the transmission), transferring power hydraulically.
Because there is no solid mechanical connection between the engine and transmission under normal low-speed conditions, the engine can continue to idle while the vehicle is stopped in gear. A stator positioned between the pump and turbine redirects fluid flow, multiplying torque at low speeds to help the vehicle accelerate smoothly from a stop.
Modern torque converters feature a lock-up clutch that mechanically locks the engine and transmission shafts at highway speeds, eliminating fluid slip and improving fuel efficiency. Symptoms of torque converter failure include slipping gears, shuddering (often described as driving over rumble strips), overheating, and transmission fluid contamination.