Sierra U-Joint Assembly 18-6401 for Mercruiser, Replaces Mercury Marine 864244A2, 12784A10

The Sierra U-Joint Assembly, part number 18-6401, is a machined replacement universal joint assembly engineered for Mercruiser sterndrive applications. It is designed as a direct cross-reference replacement for Mercury Marine universal joint assemblies, allowing boat owners and marine technicians to restore proper drive-line articulation between the engine coupler and the sterndrive without sourcing a discontinued or hard-to-find OEM part.

This U-joint assembly features a machined exterior finish for consistent fit and smooth operation under the torsional loads typical of sterndrive power transfer. It is built to Sierra's standard for Mercruiser U-joint and yoke components, making it a straightforward swap for technicians already familiar with servicing Mercruiser drive-line hardware.

Because drive-line components like this carry significant rotational load, the assembly is constructed as a substantial, solid unit rather than a lightweight stamped part. Boat owners replacing a worn, notchy, or failed U-joint should confirm their existing part matches the Sierra 18-6401 or one of its OEM cross-reference numbers before ordering.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-6401
• Product Name: U-Joint Assembly
• Category: Mercruiser U-Joints and Yokes
• Weight: 10.94 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• Exterior Finish: Machined
• UPC: 808282111830
• OEM Cross Reference: 864244A2, 12784A10

Fitment

Designed for Mercruiser sterndrive U-joint and yoke applications.

Replaces (OEM)

• 864244A2
• 12784A10

Frequently Asked Questions

What is Sierra part number 18-6401? It is a U-Joint Assembly designed for Mercruiser sterndrive applications, providing the universal joint connection used in the drive-line between the engine coupler and the sterndrive.

Does the Sierra 18-6401 replace Mercury Marine parts? Yes, the Sierra 18-6401 U-Joint Assembly cross-references to Mercury Marine part numbers 864244A2 and 12784A10.

How much does the 18-6401 U-Joint Assembly weigh? The Sierra 18-6401 U-Joint Assembly weighs 10.94 pounds.

What are the dimensions of the 18-6401 U-Joint Assembly? The listed product dimensions for the Sierra 18-6401 are 0.39 x 0.39 x 0.39 inches.

What finish does the 18-6401 U-Joint Assembly have? The Sierra 18-6401 has a machined exterior finish.

Is the Sierra 18-6401 an OEM part or an aftermarket replacement? The Sierra 18-6401 is an aftermarket U-Joint Assembly manufactured by Sierra as a direct cross-reference to Mercury Marine OEM part numbers 864244A2 and 12784A10.

What application is the 18-6401 U-Joint Assembly used for? It is categorized for Mercruiser U-joints and yokes, used in the sterndrive coupling of Mercruiser-equipped boats.

How do I know if I need the Sierra 18-6401 U-Joint Assembly? If your existing U-joint assembly carries the Mercury Marine part number 864244A2 or 12784A10, or shows wear such as play or roughness in the joint, the Sierra 18-6401 is the correct cross-reference replacement.

Is the 18-6401 currently in production? Yes, the Sierra 18-6401 U-Joint Assembly is not discontinued by the manufacturer.

What is the UPC for the Sierra 18-6401 U-Joint Assembly? The UPC for the Sierra 18-6401 U-Joint Assembly is 808282111830.