Litens Automotive is the original equipment supplier to GM for this decoupling alternator pulley. This replacement pulley is also designed and produced by Litens and is exact in all form, fit, and performance characteristics as the original equipment part (with the exception of not having the car manufacturer's logo or part number applied to the part). Decoupling pulleys are engine specific and should never be interchanged with other types of pulley technology. The Litens OAD type pulley is designed to free-wheel in one direction and, with an internal spring and damping device, softly engage in the opposite direction. The OAD is designed as a sacrificial part of the front-end accessory drive system, protecting other belt driven component as well as the alternator. The correct decoupler pulley ensures smooth, quiet performance as well as increasing vehicle gas mileage. Under normal driving conditions, the original pulley will require replacement in approx. 35,000 - 50,000 miles. Fits Chevy Impala Police Vehicles 3.9L with cylinder deactivation. Litens is the world's largest supplier of original equipment (O.E.) power transmission products. At Litens, we design systems that are more efficient, resulting in tangible fuel economy/emissions benefits. Litens holds over 2000 patents and continues to respond to the ever-changing automotive industry by investing heavily in new technology, facilities, and people. 90% of our line is made of products coming from the OE manufacturer, which makes the Litens Tensioning Products portfolio the purest OE tensioning line in the North American aftermarket.