Mercury – Complete Gearcase | Bravo One / One X Series | Corrosion-Resistant Alloy | 8866A63

Overview

There’s a moment every boater knows — that quiet pause right before you throttle up, waiting for the boat to answer. When everything is working the way it should, the response is instant: smooth lift, clean power, and a feeling that the whole boat is tuned to your touch. That kind of confidence starts deep inside the drive system. The Mercury Marine part number 8866A63 Complete Gearcase is built for boaters who count on that feeling every time they leave the dock. Whether you’re carving through open water or easing into a slip at sunset, this gearcase is designed to keep your Bravo One or One X running exactly the way it was meant to.

Key Features

• Complete replacement gearcase for MerCruiser Bravo One (serial 0D649909 and up) and Bravo One X sterndrives
• Compatible with 1.36, 1.50, and 1.65 gear ratios
• Durable Tri-Paint protective system for long-term corrosion resistance
• XK360 low-copper alloy engineered to resist pitting and wear
• Heavy-duty forged gears and reinforced U-joint for reliable, long-term service
• Designed to meet OEM specifications for precise fit and smooth performance

Engine & Boat Compatibility

• Fits MerCruiser Bravo One sterndrives (serial number 0D649909 and newer)
• Fits Bravo One X sterndrives using 1.36, 1.50, and 1.65 gear ratios
• Ideal for performance boats, offshore cruisers, bowriders, sport runabouts, and high-horsepower recreational vessels
• Works for both single-engine and twin-engine applications

Performance & Practical Benefits

A worn gearcase has a way of revealing itself — sloppy shifts, sluggish holeshot, and a subtle vibration that takes the fun out of an otherwise perfect day. Replacing it with the 8866A63 brings everything back into alignment. Shifts become crisp and confident, acceleration feels smooth and connected, and the boat responds to the helm with that steady, predictable feel you expect from a Bravo drive.

Durability is where this gearcase really shines. The forged gears are designed to handle the stress of high-output engines, while the low-copper alloy and multi-layer Tri-Paint system protect the housing from saltwater corrosion and years of heavy use. It’s the kind of design that lets you push the boat when you want to and relax when you need to — without worrying about what’s happening under the surface. Installation is clean and straightforward, and once mounted, the gearcase settles into its role with quiet, dependable strength.

Why Buy OEM

When you’re talking about a major drivetrain component, there’s no room for guessing. A genuine Mercury Marine part gives you the precision and reliability that aftermarket assemblies just can’t match. Every surface, every internal angle, every coating thickness is engineered around the exact demands of a Bravo One or One X system. Aftermarket versions may look similar, but they rarely offer the same corrosion protection or long-term gear strength. Choosing OEM means your boat runs the way the designers intended — tight, smooth, and ready for long days on the water.

FAQ

Q1: Which systems does the Complete Gearcase 8866A63 fit?

It fits MerCruiser Bravo One sterndrives (serial 0D649909 and up) and Bravo One X drives using 1.36, 1.50, or 1.65 gear ratios.

Q2: What makes this better than aftermarket gearcases?

The materials and engineering. Mercury’s forged gears, corrosion-resistant alloy, and Tri-Paint coating deliver durability aftermarket options usually can’t match.

Q3: How do I know if this is the correct replacement?

Check your sterndrive model and gear ratio. If you have a Bravo One (0D649909 or newer) or a Bravo One X, this part number typically fits.

Q4: Can it be used in both saltwater and freshwater?

Absolutely. It’s designed to endure harsh saltwater conditions, so freshwater performance is no issue at all.

Q5: Is installation straightforward?

Yes. As a complete assembly, installation follows standard Bravo One procedures and fits cleanly when paired with the correct drive series.