UPPER TRANSMISSION SHAFT 5000618 REC5000618

Function and Technical Context

The upper drive shaft is the component responsible for transferring torque from the drive shaft of the bevel gear set to the propeller, operating in the upper section of the outboard or inboard stern housing. It forms part of the lower drive train, and its proper functioning is essential for maintaining synchronization between the drive bevel gear and the driven bevel gear. Advanced wear or a breakage of this shaft can result in a total loss of propulsion, progressive damage to the bevel gears in the lower unit, and saltwater ingress through the seals if the shaft operates with excessive play. Part number 5000618 is designed to be installed in the upper position within the drive assembly and is compatible with OMC, Mercury, and Mariner equipment according to documented manufacturer equivalencies.

When should this part be replaced?

The most common signs of wear on an upper drive shaft include abnormal vibration or a dry metallic noise in the transom during operation, difficulty or knocking when shifting between forward, neutral, and reverse, and noticeable play when manually moving the shaft after the lower unit has been removed. It is recommended to inspect the condition of the shaft, its splines, and the associated seals during every seasonal service or every 200–300 hours of operation, coinciding with the lower unit oil change. Replacing the shaft as a preventive measure upon detecting the first signs of wear on the splines prevents major drivetrain failures that could leave the boat inoperable at sea.

Compatibility Chart

Equivalent Manufacturer Part Numbers