How to Remove and Reinstall a Sterndrive for Service

Find your drive's model and serial number and get the service manual for it. Order the full gasket and O-ring kit before you start, plus bellows if they are due. Have the hinge pin tool, alignment tool and any other special tools on hand. A boat sitting for weeks with the drive off while you wait for parts is a boat that gets rained into.

Put the boat on its trailer or stands, out of the water, level and chocked. Disconnect the battery and remove the key. Trim the drive to the position your manual describes. Take photos of everything at the back of the boat: the trim cylinders, hoses, the shift cable area, any wires or sensors.

Remove the prop and its hardware, keeping the parts in order. Then put the remote control in the gear your service manual specifies for drive removal. The required position differs between drive models and years, and getting it wrong can make the shift cable hard to disconnect or reconnect, so check rather than guess.

Remove the trim cylinder pins or anchor hardware that hold the cylinders to the drive, as your manual shows. Boating Magazine suggests resting the cylinders gently against the boat and tying them up with cord so they do not swing, scratch the hull or strain their hoses. Do not open the trim hydraulic lines.

Depending on the drive, you may need to remove the speedometer pickup tube, a bonding (continuity) wire or a trim sender lead. Label each one and photograph it before you disconnect it.

Put the stand, padded blocks or your helper in place under the drive. Remove the nuts that hold the drive to the bell housing in the order your manual gives. A good tip from Boating Magazine: leave a couple of nuts threaded just onto the ends of the studs so the drive cannot pop off before you are ready. Drives are heavy; Boating Magazine puts a Bravo drive at about 180 pounds, and even smaller drives call for two people.

Work the drive loose gently and evenly, never by prying on the gasket surfaces. Once the drive has moved back far enough to reach inside, disconnect the shift cable from the drive as your manual describes, then slide the drive off the studs and set it on the stand. Cover or plug the open passages so nothing falls in.

With the drive off, look at all the bellows and their clamps for cracks, brittle or chafed rubber, and corrosion. Check the transom assembly for corrosion, the exhaust passage for damage, and the shift cable for fraying or stiffness. As BoatUS advises, if one bellows is worn, replace all of them. Our bellows and gimbal guide covers bellows replacement in more detail.

Reach through the bellows and turn the gimbal bearing by hand. It should feel smooth, with no roughness, grinding, play or rust weeping out. A rough bearing is the usual source of a growl when you turn under power. Removing and installing a gimbal bearing needs special pullers and drivers and often ends up as a shop job. On the drive, flex each U-joint by hand: any notchy feel, play or rust at the caps means the joints need attention.

Engine alignment is checked with an alignment tool that slides through the gimbal bearing into the engine coupler. Boating Magazine quotes a technician who says the tool should slide in and out with fingertip pressure; if it binds, the engine needs to be moved on its mounts. Poor alignment wears out the coupler and gimbal bearing quickly. If you do not have the correct tool for your drive, have a shop do this step while the drive is off. Our engine alignment guide explains what is involved. Mercury's owner FAQ explains why this is a recurring check: engines can drift out of alignment with the transom assembly over time, the coupler lasts longest when alignment is accurate, and damage from poor alignment or a dry coupler is not covered by its limited warranty. Lubricate the coupler splines with the grease your engine maker specifies.

Scrape the mating surfaces clean with a plastic scraper, without gouging the metal. Fit all the new gaskets and O-rings from the kit, including any in water and exhaust passages, exactly as the manual shows. Coat the U-joint shaft splines and the O-rings with the grease your manual specifies; Boating Magazine stresses greasing the splines and never reusing old gaskets. Grease any fittings on the U-joints if your drive has them.

With a helper, lift the drive into position, reconnect the shift cable as the manual describes, then line up the splines and slide the drive home. Turning the propeller shaft slightly can help the splines engage. Never force the drive or pull it in with the nuts; if it does not slide on, find out why. A drive that stops an inch or so short is one of the most common reinstall headaches owners report. Usual suspects: splines not lined up with the coupler (rotate the prop shaft a little and try again), rust or dried grease on the drive shaft or its O-rings, and a gimbal bearing that isn't centered, especially after it was replaced, which is what the alignment check is for. If it still won't seat, stop and have a shop look rather than forcing it. Install the nuts and tighten them in the sequence and to the torque in your service manual, not by feel.

Reinstall the trim cylinders and their pins, the speedometer tube, bonding wire and any sensors. Reinstall the prop. Reconnect the battery. With the engine off, check that the shift moves smoothly into forward, neutral and reverse and that the prop turns the right way in each gear (rotate it by hand, carefully, with the key removed). Trim the drive fully up and down and steer lock to lock to check nothing binds or pulls. Then run the engine on a flush setup your manual approves for that drive, or on the water, and check for leaks and correct shifting. Check the bilge right after launching and again after the first run.