The Mercury Upper Driveshaft Bearing is one of the most important components inside any Mercury lower unit. Replacing Mercury part numbers 31-36387A1 and the current superseded part number 8M0146566, this precision tapered roller bearing supports the upper end of the driveshaft while maintaining proper alignment between the driveshaft, pinion gear, forward gear, and reverse gear.
Proper alignment minimizes friction, reduces gear wear, and helps maximize gearcase life. Whether you're rebuilding a stock fishing motor or a high-horsepower Mercury Racing lower unit, replacing a worn 36387 A1 or 8M0146566 upper driveshaft bearing is inexpensive insurance against costly gearcase failure.
Premium OEM-Spec Quality
This premium replacement for Mercury 36387A1 and 8M0146566 is manufactured to meet or exceed OEM specifications for fit, dimensional accuracy, load capacity, and durability.
Produced using premium bearing steel, precision-ground races, and strict bearing manufacturing standards, it delivers the strength and reliability required for both recreational and high-performance Mercury applications while providing a cost-effective alternative to the factory bearing.
This bearing also cross-references to Sierra 18-1143, GLM 21580, and 1143P, making it a direct replacement for Mercury 36387A1 and 8M0146566 across numerous Mercury Marine and Mercury Racing gearcases.
Engineered for High-Performance Mercury Gearcases
Mercury selected a tapered roller bearing design because it supports both radial and thrust loads while maintaining precise gear alignment under heavy acceleration and sustained high RPM. Proper preload on Mercury 36387A1 and 8M0146566 upper driveshaft bearings is essential for maintaining correct gear backlash, minimizing vibration, and maximizing gear life. A worn upper driveshaft bearing allows driveshaft movement that accelerates pinion gear wear, increases operating temperatures, and can eventually result in catastrophic lower unit failure.
This premium replacement bearing is built to handle the severe loads encountered in bass boats, offshore boats, recreational outboards, and Mercury Racing applications producing well over 300 horsepower.
Common Signs of Bearing Wear
As a Mercury 36387A1 or 8M0146566 upper driveshaft bearing begins to wear, the gearcase often develops excessive driveshaft movement, metallic particles in the gear lubricant, rough shifting, vibration, rumbling gear noise, or premature pinion gear wear. Water intrusion, contaminated lubricant, improper preload, or simply years of service can all shorten bearing life. Replacing the upper driveshaft bearing during a lower unit rebuild helps restore proper gear alignment while protecting expensive gears, shafts, seals, and bearing carriers.
Professional Installation
Whenever replacing Mercury upper driveshaft bearing 36387A1 or 8M0146566, inspect the bearing cup, driveshaft, pinion gear, seals, water pump components, and carrier assembly for wear or damage.
Proper bearing preload, gear backlash, and gear tooth contact should always be verified during assembly. Every rebuilt Mercury lower unit should also be pressure and vacuum tested before being returned to service to ensure long-term reliability.
Extensive Mercury Marine & Mercury Racing Fitment
Replacing Mercury part numbers 36387A1 and 8M0146566, this upper driveshaft bearing fits an extensive range of Mercury Marine and Mercury Racing lower units found on 2-stroke 2.0, 2.4, 2.5, 3.0, and 3.2 Liter outboards as well as newer 4-strokes.
Applications include numerous V-135, V-150, V-175, V-200, XR-2, XR-4, XR-6, Magnum II, Magnum III, XRi, EFI, Pro Max, Super Magnum, Offshore, Marathon, Jet, Sport Jet, 2.5 Liter and 3.0 Liter V6 gearcases, along with many FourStroke, SeaPro, Pro XS, Verado, and V6 and V8 outboards.
For Mercury Racing applications, Mercury 36387A1 and 8M0146566 fit many 245 Carb, 260 EFI, 280 ROS, 300 Drag, 300XS, 200R, 250R, 300R, 300 ROS, 400R, and 450R lower units.
This bearing is commonly used in 2.4 Liter CLE, 2.5 Liter SportMaster, and 3.0 Liter SportMaster and TorqueMaster gearcases. It is compatible with both single upper bearing gearcases and stacked with the double upper bearing configurations found in many Mercury Racing and heavy-duty performance applications.
As with all Mercury replacement parts, fitment should always be verified by engine serial number.
Why Bearing Quality Matters
The upper driveshaft bearing directly determines pinion gear alignment inside the lower unit. Even slight dimensional variations can affect preload, backlash, and gear tooth contact.
This replacement for Mercury 36387A1 and 8M0146566 is manufactured to premium bearing industry standards, providing the precision, durability, and load capacity required by professional lower unit builders, Mercury technicians, and high-performance racers.
Why Buckshot Racing #77
Whether you're rebuilding a classic XR-6, servicing a Pro Max, maintaining a SportMaster, refreshing a TorqueMaster, or assembling a championship-winning Mercury Racing gearcase, this premium replacement for Mercury 31-36387-A1 and 8M0146566 delivers OEM-spec fit, precision, and durability without the OEM price.
Built to strict bearing manufacturing standards and trusted by racers, mechanics, and engine builders, it provides the reliability needed to keep your Mercury lower unit performing at its best.