The flywheel for most automatic transmissions/transaxles is simply a stamped-steel disc with a ring gear located at the outer edge for engagement with the starter’s pinion gear. With this type of flywheel, the torque converter has no ring gear. Some cars use a more modest flywheel known as a flexplate, which is all that’s needed because the torque converter itself has a ring gear located on its outer edge.
The flywheel, or flexplate, mounts to the engine's crankshaft and also serves as a mounting location for the torque converter. Consequently, the flywheel or flexplate transmits engine torque to the torque converter housing. The flywheel’s ring gear also serves as an engagement point for the pinion of the starter motor when cranking the engine. Because of the lightweight design of the flywheel or flexplate, it does not help to smooth out power pulses from the engine like the flywheel does on a car with a manual transmission. On cars with automatic transmissions, the torque converter provides this function.
The flywheel/flexplate does not require regular maintenance. Sometimes, the ring gear may suffer damage from improper starter engagement or alignment. If this is the case, the ring gear or flywheel may need replacement.