How to Repair the Lower Shifter on a Mercury Outboard 90 HP

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When the gear shift on a Mercury outboard engine begins to feel stiffer than normal, the engine may have a bent lower shift rod. If you need to repair the lower shifter on your Mercury outboard, you can purchase a kit with all of the parts required to make the repair. If you are a boater with extensive experience with outboard care and repair, this kit, some marine grease and a few tools will allow you to complete the project with little trouble.

Items you will need

  • Shift rod kit

  • Waterproof marine grease

  • Snap-ring pliers

  • Thread locker

  • Torque driver

  • 5/16-inch box-end wrench

  • Propeller wrench

Step 1

Coat the shift rod guide, three new O-rings and the shift rod seal from the shift rod kit with waterproof marine grease. Install the shift rod guide assembly in the shift rod housing, inside the engine's exhaust tunnel. Install the smallest washer and seal from the shift rod kit into the shift rod.

Step 2

Smear a light coating of marine grease on the cover O-ring for the gear case top cover. Set the cover in place. Insert the shift rod downward, through the top of the cover. Fit the large washer and the shift rod pin from the shift rod kit onto the shift rod.

Step 3

Secure the shift rod spring and collar on the other end of the shift rod with the snap-ring from the kit, using snap-ring pliers. Line up the shift rod with the shift rod detent cam. The detent cam is an oblong plate with a spring and a ball at its center, located at the bottom of the shift rod housing. It creates the feeling of a "bump" as you pass between gears when operating the boat. The cam must face the rear of the gear case. Install the cam, using the pin from the shift rod kit.

Step 4

Attach the magnet from the shift repair kit to the shift rod so the magnet is to the back of the gear case when installed. Position the shift detent plate, spring and ball into the shift detent bore of the gear case. Install the shift rod assembly so the shift cam groove faces aft. Move the cam to the "Neutral" position.

Step 5

Dab thread locker onto the shift rod cover bolt threads and the dowel pin of the shift rod cover. Push the dowel pin into place on the cover and install the cover on the gear case. Thread the bolts into the bores on the gear case by hand. Tighten them to 45 inch-pounds of torque with a torque driver.


  • Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box. After the work is complete, reconnect the negative battery cable.
  • Whether you work on your outboard motor on the boat or on a storage stand, remove the propeller nut with a wrench. Slide the thrust hub, propeller and washers from the propeller shaft. Failure to remove a propeller before operating an outboard out of the water during maintenance or long-term storage is an invitation to a propeller-strike injury, which can maim or kill.
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