Alternator Overrun Pulley with lid suitable for Mercedes-Benz. Product Information: Robust construction for perfect function; Optimal fitting accuracy for easier repairs; Strict quality standards; Compliance with the requirements of vehicle manufacturers. Vehicle Repairs. We've Got What It Takes. Combustion engines do not have a uniform rotary motion. Due to the four-stroke principle, the crankshaft is constantly accelerated and braked. These vibrations are also transmitted to the power unit drive and generate high torque fluctuations, especially on the relatively heavy generator rotor. In modern vehicles, the generator is equipped with an alternator overrun pulley. It is mounted directly on the drive shaft of the generator and transmits the driving force only in one direction of rotation. This decouples the generator from the vibrations of the crankshaft. The advantage: the belt drive runs smoother and quieter and the service life of the drive belt is extended. For this reason, febi only offers alternator overrun pulleys in OE matching quality. Quality by Conviction. If the alternator overrun pulley is stuck, engine vibrations are no longer compensated and lead to unsteady belt running at low engine speeds. Due to the increased movements of the belt, high forces act on the tensioning element which can cause both this and the fixed alternator overrun pulley to fail prematurely. In the worst case scenario, this can result in serious engine damage. Alternator overrun pulleys from febi are therefore intensively tested. Our quality management tests the offered components for various requirements and loads, e.g. accuracy of fit, dimensional accuracy, material quality, and tensile strength. Characteristics of Various Freewheels. Currently two different freewheels are used: the Overrunning Alternator Pulley (OAP) and the Overrunning Alternator Decoupler (OAD). The OAP has a simple, overrunning clutch located inside the running disc. When the engine is switched off, the generator rotor runs out due to the large mass without taking the pulley with it. In contrast, the OAD has a torsion spring in addition to the freewheel function where energy can be absorbed. It absorbs rotational irregularities emanating from the crankshaft before these can have a negative influence on the generator and therefore also on the auxiliary drive.