Mercury MerCruiser Double Yoke / Center Socket – U-Joint Assembly 393831

The Mercury MerCruiser 393831 is a genuine OEM double yoke / center socket used in the U-joint driveline assembly on selected MerCruiser sterndrives. This component sits between the two U-joint cross-and-bearing assemblies and forms the center connection that allows the driveline to transmit power while accommodating the movement and steering articulation of the drive. One is required per U-joint assembly.

Compatible Applications

• R / MR / Alpha One Sterndrive — 1983–1990, serial range 6225577 through 0F386995
• R / MR / Alpha One Transom Assembly — 1983–1990, serial range 6216687 through 0F386995
• Selected Bravo, Bravo Two, and Bravo Three applications — serial range varies by drive generation

Always confirm fitment using the sterndrive serial number and the applicable Mercury parts diagram. Bravo applications vary by generation and serial range.

Serial Number & Fitment Notice

Confirm the sterndrive serial number before ordering. MerCruiser used different U-joint assemblies, yokes, and center sockets across Alpha One and Bravo drive generations. Part 393831 must be matched to the specific drive parts diagram — engine model and horsepower alone are not sufficient to confirm fitment. Later drives (approximately 2000 and newer) may use a larger center socket; verify the bore dimensions match your application.

Product Details

• OEM Part Number: 393831
• Also Referenced As: 39383, 39383T (earlier Mercury references)
• GTIN: 745061141179
• Function: Double yoke / center socket — U-joint driveline assembly
• System: Sterndrive driveline / universal joint assembly
• Quantity Required: 1 per U-joint assembly
• Bore Diameter: 1.079 in. (for matching U-joint cross-and-bearing assemblies)

When to Replace

Inspect the double yoke whenever servicing the U-joint assembly. Replace if the yoke shows any of the following:

• Worn or damaged bearing-cap bores
• Corrosion, pitting, or rust damage
• Cracking or visible deformation
• Excessive driveline play or vibration
• Damage caused by a failed U-joint cross or bearing
• Uneven or loose fit around the bearing caps

A worn center yoke can cause repeat U-joint failures even after installing new cross-and-bearing kits — if the bores are damaged, the yoke itself must be replaced.

Installation Notes

When replacing the double yoke, inspect both U-joint cross-and-bearing assemblies and the adjoining coupling and gear-end yokes at the same time. Mercury diagrams show two cross-and-bearing assemblies used with this center yoke. Ensure bearing caps seat fully and that the assembled U-joints articulate smoothly without binding or excessive looseness. Follow the appropriate Mercury MerCruiser service manual for assembly procedures, lubrication specifications, and driveline inspection intervals.

Alternate / Superseded Part Numbers

• 393831
• 39383
• 39383T

Mercury parts diagrams show 393831 as the current replacement for earlier 39383 / 39383T references.

Related Parts

• Mercury / MerCruiser U-Joint Cross & Bearing 866136A01
• Mercury / MerCruiser U-Joint Cross & Bearing 805536A2
• Mercury / MerCruiser U-Joint Cross & Bearing 75832T
• Sierra Heavy-Duty U-Joint 18-2104 – MerCruiser / OMC / Volvo Penta

Parts Desk Insights

Best Use Case: This is the right part when a U-joint failure has damaged the center yoke bores — not just a routine cross-and-bearing replacement. If a customer is experiencing repeat U-joint problems after installing new bearings, the double yoke is the first place to look. It's also commonly needed during a full driveline rebuild on older Alpha One and early Bravo drives.

Common Issues: The most frequent mistake is ordering this part based on engine model or horsepower instead of confirming the sterndrive serial number. The 393831 center socket has a 1.079 in. bore — later drives use a larger bore center socket that is not interchangeable. If the serial number falls outside the listed range, check the drive diagram carefully before ordering.