Yamaha Shifter 6U1-18421-00-00. Overview. The Yamaha Shifter 6U1-18421-00-00 is a genuine original equipment manufacturer component designed to enable precise gear selection and smooth shifting within your Yamaha system. This essential part plays a key role in controlling gear engagement, ensuring reliable operation and responsive handling.. Engineered to Yamaha's exact specifications, this shifter provides a precise fit and dependable performance. It is an ideal replacement for worn or damaged