Mercury - Upper Driveshaft Housing Bravo One XR Series Corrosion-Resistant Marine Alloy 863836A56. Overview. Every boater knows that the real magic of a good day on the water comes from trust-trust that when you push the throttles forward, your boat responds with smooth, confident power. That's why having a solid upper driveshaft housing matters so much. You feel it in the way the drive holds steady through tight turns, in the calm rise onto plane, and even in the quiet hum at cruising speed. Wi