Sierra 18-6406 U-Joint Assembly, Replaces 865493A01/865496A01, for Mercruiser Alpha I, Alpha I SS & Bravo Stern Drives

The Sierra 18-6406 U-Joint Assembly is a replacement universal joint built for Mercruiser stern drive units, connecting the drive shaft to the transmission and lower unit so power transfers smoothly through the drive's articulation points. A worn or failing U-joint can cause vibration, clunking, or play in the drive train, and replacing it with a properly fitted assembly like the 18-6406 restores smooth, reliable power transfer.

This assembly includes both a straight and a 90 degree grease fitting, giving the installer flexibility to choose the fitting orientation that best suits the access and grease gun setup on the specific installation. It is designed to fit Mercruiser Alpha I units from serial number B418819 and above, as well as Alpha I SS and Bravo drives, making it a common service part for these Mercruiser drive families.

The 18-6406 cross-references directly to Mercury Marine OEM part numbers, so it can be used as a like-for-like replacement on applicable Mercruiser units without altering fit or function versus the original equipment part.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-6406
• Product Name: U-Joint Assembly
• Includes: Straight grease fitting and 90 degree grease fitting
• Fitment: Mercruiser Alpha I (S/N B418819 and above), Alpha I SS, Bravo
• Weight: 1.04 pounds
• UPC: 808282182618

Fitment

• Mercruiser Alpha I units, serial number B418819 and above
• Mercruiser Alpha I SS
• Mercruiser Bravo

Replaces (OEM)

• 865496A01
• 865493A01
• 865510T
• 865511T

Frequently Asked Questions

What does the Sierra 18-6406 U-Joint Assembly fit? It is designed for Mercruiser Alpha I units with serial number B418819 and above, as well as Mercruiser Alpha I SS and Bravo stern drives.

Which OEM part numbers does the 18-6406 replace? The 18-6406 replaces Mercury Marine OEM numbers 865496A01, 865493A01, 865510T, and 865511T.

Is the 18-6406 a direct equivalent to the Mercury Marine 865493A01 and 865496A01 U-joints? Yes, the Sierra 18-6406 U-Joint Assembly cross-references directly to Mercury Marine 865493A01 and 865496A01, so it installs as a like-for-like replacement on applicable Mercruiser drives.

What grease fittings come with this U-joint assembly? The 18-6406 U-Joint Assembly includes both a straight grease fitting and a 90 degree grease fitting, so the installer can choose whichever orientation fits the available access.

How much does the 18-6406 U-Joint Assembly weigh? The Sierra 18-6406 U-Joint Assembly weighs 1.04 pounds.

Will this U-joint work on any Mercruiser Alpha I drive? It fits Mercruiser Alpha I units from serial number B418819 and above; earlier serial number Alpha I units are not covered by this listing, so check the drive's serial number before ordering.

Does the 18-6406 fit Bravo drives as well as Alpha units? Yes, in addition to Alpha I (S/N B418819 and above) and Alpha I SS, the 18-6406 U-Joint Assembly also fits Mercruiser Bravo drives.

Is the Sierra 18-6406 a genuine OEM part or an aftermarket replacement? The 18-6406 is a Sierra-branded replacement U-joint assembly engineered to replace the listed Mercury Marine OEM numbers, rather than a Mercury-branded original part.

What is included in the box with the 18-6406 U-Joint Assembly? The assembly ships complete with the U-joint and its two grease fittings, a straight fitting and a 90 degree fitting.

Why would I need to replace the U-joint on my Mercruiser stern drive? A worn U-joint assembly like the one replaced by the Sierra 18-6406 can develop play or wear at the drive shaft connection, and replacing it restores proper alignment and power transfer between the transmission and the lower drive unit.