Starter Drive
The gear mechanism within the starter motor that extends to mesh with the flywheel ring gear and transfer cranking power.
A starter drive (historically referred to as a Bendix drive or starter clutch) is the mechanical gear mechanism inside the starter motor assembly. Its primary job is to engage the starter motor's drive shaft with the engine's flywheel ring gear to crank the engine and then disengage once the engine fires up.
The starter drive features a small pinion gear and a built-in one-way overrunning clutch. When the ignition is turned on, the starter solenoid pushes the starter drive forward, sliding the pinion gear along splines to mesh with the flywheel teeth. The one-way clutch allows the starter to drive the engine, but if the engine starts and spins faster than the starter, the clutch slips, preventing the engine from over-spinning and destroying the starter motor.
Over time, the starter drive can fail. The internal one-way clutch can wear out, causing it to slip under load. When this happens, the starter motor will spin with a whining sound, but it will fail to turn the engine over. The pinion gear teeth can also chip or wear down, causing grinding noises during starting.
If the starter drive fails, it is usually replaced by installing a complete new or rebuilt starter motor assembly, as rebuild services are widely available and cost-effective.