a slue position sensing system and method of modifying a machine to include such a slue position sensing system are disclosed . the slue position sensing system may include a swing sensor housing disposed between a swing motor and a swing drive . the swing sensor housing may be coupled to a rotary position sensor that indirectly detects rotation of the target gear or a speed sensor that directly detects rotation of the target gear . for embodiments with no target gear , but with upper and lower frames rotatably coupled together by a ring gear and a swing gear , the sensor may be a rotary position sensor mounted to a slip ring assembly and magnet that are connected to a hydraulic swivel between the upper and lower frames or the sensor may be a speed sensor that detects rotation of the swing gear . the sensors generate a signal that is communicated to a controller or an ecm that accurately reflects the angular movement imparted to the work implement by the swing drive .