Yamaha - Lower Unit Assembly Complete Drivetrain Assembly 6FM-45300-00-CD. Overview. The Yamaha Lower Unit Assembly 6FM-45300-00-CD is what takes all the power from your engine and actually puts it to work in the water. When something inside the lower unit starts to fail, you'll feel it quick-noise, vibration, or loss of performance under load. Instead of chasing worn gears or internal damage piece by piece, replacing the full assembly is usually the most reliable way forward. It gives you a solid, ready-to-run setup so you can get back on the water without second-guessing it.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for dependable operation.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Smooth Power Transfer - Supports efficient thrust and consistent performance across all speeds.. • Corrosion-Resistant Construction - Designed to withstand harsh marine environmen