Only the best mechanics get this creative

Did you know that many modern car alternators have a built-in one-way clutch inside the pulley?! 🚗⚡
On older vehicles, the alternator pulley was a solid piece of steel bolted directly to the rotor shaft. However, modern engines experience sudden deceleration whenever the transmission shifts or the throttle closes. Because the internal rotor of an alternator is heavy and spins at high RPM, sudden engine slowdowns can cause the serpentine belt to violently vibrate, slip, and wear out prematurely.
To fix this, automotive engineers created Overrunning Alternator Decoupler (OAD) pulleys. In this test, a technician wraps string around the pulley to rip-cord spin the alternator up to speed. When he stops the internal rotor with a tool, the outer pulley continues to smoothly freewheel! If this one-way clutch seizes up, your engine belt will squeal and chatter aggressively.