Yamaha - Lower Unit Assembly Outboard Drivetrain 6KA-45300-00-8D. Overview. You can usually tell when a lower unit is starting to give out-noise, rough shifting, or it just doesn't feel right under load. This is the kind of replacement that brings everything back to solid, dependable operation. Once it's bolted up, you get that smooth engagement and steady push through the water again. It's one of those parts you install and then don't have to think about.. Key Features. Smooth Power Transfer - Delivers consistent engine output to the propeller with minimal vibration.. Corrosion-Resistant Housing - Built to handle harsh marine environments, including saltwater use.. Factory-Spec Fitment - Designed for proper alignment and seamless installation on Yamaha outboards.. Durable Internal Gearing - Supports long-term reliability under regular use and load.. Complete Assembly Unit - Pre-assembled design simplifies replacement and reduces downtime.. Engine & Boat Compatibility. Designed for Yam