Fits all four versions of the Bosch alternators...90, 120, 150 and 200 Amp
THIS IS AN EXTREMELY CRITICAL PART. Manufactured by INA, the OEM supplier to both Bosch and Mercedes Benz.
If you have had problems with broken or thrown serpentine belts or a broken belt tensioner arm or roller, this decoupling or declutching pulley has most likely failed. When operating correctly, this unit has a one-way clutch to minimize belt flutter and therefore, stress. Over time, this pulley will seize, thereby losing its one-way decoupling/declutching action and cause failure of other components. To check the integrity of your
alternator pulley, simply remove the belt and place a screwdriver into
the front of the alternator cooling fan to stop the armature from
rotating. Then turn the pulley by hand. If it moves one direction but,
not the other, it is functional. If it will not rotate at all, it has
Video demonstration of why the declutching pulley is a critical component: http://www.youtube.com/watch?v=4EXYP1CmL9Q&feature=relate