Yamaha - Shift Rod Assembly Gearcase Shifting Component 6H4-JD001-21-50. Overview. When a motor isn't dropping cleanly into gear, I usually start looking down at the shift linkage, and this assembly is a big part of that system. It's responsible for translating what you do at the control into actual gear engagement in the lower unit. Over time, wear or slight bends can throw things off and make shifting feel inconsistent. Replacing the full assembly brings everything back into line and gives you