Yamaha - Gear 1 Assembly Lower Unit Gear System 6L6-45560-00-00. Overview. When gears start wearing out inside the lower unit, you'll notice it fast-clunking shifts, slipping under load, or just a rough feel overall. This is one of those internal parts that makes or breaks how smoothly your outboard runs. Swapping in a fresh Yamaha gear assembly brings back that solid, quiet engagement you expect. It's the kind of repair that restores confidence, especially when you're running longer trips or ca