Yamaha - Lower Unit Assembly Complete Drivetrain Assembly 6FM-45300-10-CD. Overview. The Yamaha Lower Unit Assembly 6FM-45300-10-CD is what turns engine power into actual movement on the water, and when it starts going bad, you feel it right away. Noise, vibration, or slipping under load are usually the first signs something's off down there. Instead of chasing individual internal parts, replacing the full unit is often the cleanest and most reliable fix. It gives you a fresh, solid setup so you can run without worrying about what's happening below the surface.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for dependable performance.. • OEM Fit Precision - Built to Yamaha specifications for direct installation and proper alignment.. • Smooth Gear Operation - Supports consistent shifting and reliable power transfer under load.. • Corrosion-Resistant Construction - Designed to handle saltwater exposure and harsh marine environments.. C