Yamaha - Gear Set Lower Unit Drive System 6AX-45550-00-00. Overview. Inside the lower unit, this gear set is what actually puts power to the water. When everything's right, you don't think about it-you just feel smooth engagement and solid push every time you throttle up. But when gears start wearing or chipping, you'll hear it and feel it quick. This Yamaha gear set is built to handle that load day in and day out, whether you're running hard offshore or making steady runs along the coast.. Key Features. Precision Gear Engagement - Designed for smooth, consistent power transfer from the driveshaft to the propeller.. Factory-Matched Tolerances - Built to exact Yamaha specifications for proper alignment and long-term durability.. Hardened Gear Construction - Engineered to handle high torque loads and repeated shifting under marine conditions.. Direct Internal Fit - Drops into the lower unit with correct clearances when installed with proper setup procedures.. Engine & Boat Compatibility.