Bendix Drive
A type of starter motor engagement mechanism that uses an overrunning clutch to connect and disconnect from the flywheel.
A Bendix drive is a type of engagement mechanism used in starter motors that allows the starter pinion gear to engage and disengage the engine's flywheel ring gear. Named after its inventor, Vincent Bendix, this system uses a splined shaft and inertia to automatically drive the pinion gear forward when the starter motor spins.
When the starter is activated, the electric motor spins, causing the pinion gear to slide forward along a helical spiral gear track on the starter shaft until it meshes with the flywheel. Once the engine starts and spins faster than the starter motor, the flywheel drives the pinion gear backward along the helix, disengaging it. This prevents the running engine from spinning the starter motor at dangerously high speeds.
Symptoms of a failing Bendix drive include a high-pitched whirring sound when turning the key (indicating the starter motor is spinning but the pinion gear failed to slide forward and engage the flywheel) or a grinding noise. A sticky or dirty Bendix drive shaft can prevent smooth engagement, requiring starter motor replacement or assembly cleaning and lubrication.