Yamaha - Shift Rod ZSM187/8 Gearcase Shifting Component 6H4-JD001-21-30. Overview. When shifting starts to feel off, this is one of the first places I look. The shift rod plays a direct role in how cleanly your lower unit moves between gears, and when it's worn or out of spec, you'll feel it right away at the control. This is one of those parts that doesn't get much attention until something's not right. Swapping it out restores that solid, positive engagement you expect from a Yamaha.. Key Feat