flexplate

A flexplate is a circular metal plate bolted to the front of an internal combustion engine's crankshaft, used in vehicles with automatic transmissions. It serves as the mounting surface for the torque converter and carries the starter ring gear that engages the starter motor to crank the engine. The flexplate is housed inside the transmission bell housing and transfers engine torque to the torque converter while also providing balance with the crankshaft.

Most flexplates are steel; some are aluminum. They typically feature an inner bolt pattern matching the crankshaft and an outer ring gear that the starter engages. The outer diameter and thickness vary by application. The plate is designed to be compact and lighter than a manual flywheel because the torque of the engine is initially moderated by the torque converter. Some designs incorporate a torsional damper to absorb engine vibrations, but others rely on the torque converter for damping.

Unlike a manual flywheel, the flexplate does not provide a friction surface for a clutch. Its primary role is to transmit engine torque to the transmission and to provide a mounting surface for the torque converter plus the starter ring gear. It must be replaced if cracked, warped, or if the ring gear is damaged, as such damage can cause vibration, poor starter engagement, or transmission misalignment.

During maintenance or replacement of the automatic transmission or engine, the flexplate is inspected and replaced if necessary. Improper installation, incorrect torque, or missing bolts can cause vibration, misalignment, or damage to the starter or transmission.