Milky gear oil. A grind going into forward. A whine that was not there last month. Your gear case is telling you something, and it never gets cheaper by waiting. We diagnose and repair marine gearboxes and lower units dockside across Fort Myers, Cape Coral, Naples, and SWFL, most of them without the boat ever leaving your lift.
Gear case diagnosis is methodical, and it happens right at your boat:
First, the oil tells its story. We drain a sample and read it: color, metal content on the magnetic plug, water contamination. Fine gray paste is normal wear; glitter and chunks are not. Second, a pressure and vacuum test proves whether the seals hold, finding the leak path before anything is disassembled. Third, we check shift engagement, propshaft play, and backlash by hand, which reveals bearing and clutch condition without opening the case. Only then do you get a diagnosis and a written quote, and only after your approval does repair begin.
Most seal jobs, water intrusion recoveries caught early, and shift repairs are completed dockside. When internal damage calls for a full teardown, we handle removal, the bench rebuild, and reinstallation, and we tell you honestly when a replacement case makes more financial sense than rebuilding yours.
Suzuki, Yamaha, and Mercury outboard lower units make up most of our gear case bench, each with its own known weak points and its own factory specs for backlash and shimming. On the sterndrive side, Volvo Penta and MerCruiser outdrives bring their own gear and bellows considerations, and Yanmar-powered boats bring saildrive and transmission questions we are equally at home with. Different hardware, same discipline: measure, pressure test, and rebuild to spec.
The gear case is the one component on your boat where a small symptom and a catastrophic failure are separated by a few running hours. Every sign below is worth a same-week call.
Gear oil should be clean amber or dark from use, never milkshake-colored. Milky oil means water is inside, usually past a propshaft seal cut by fishing line. Water displaces lubrication and rusts bearings from the inside. This is the single most common gearbox killer in SWFL, and caught early it is a seal job, not a rebuild.
A healthy gear case shifts with a firm, single click. Grinding into forward or reverse points to worn clutch dog teeth or shift linkage problems. Every grinding shift rounds those teeth further, and rounded teeth do not un-round.
A rising whine that tracks with speed usually means bearing wear or gear mesh damage, often the after-effect of a past water intrusion nobody caught. Bearings give warning for a while. Then they don't.
If the boat drops out of gear under load, the clutch dog is worn past its limit. This one strands people, typically at the worst navigational moment available.
Gear lube weeping from seams or the prop hub means a seal has surrendered. Where oil leaks out, water gets in, and you are back to warning sign number one.
Propshaft, driveshaft, and shift shaft seal replacement, including line-cut damage
Water intrusion recovery
full flush, bearing inspection, seal replacement, and fresh lube
Bearing and gear replacement for worn or damaged internals
Clutch dog and shift component repair for grinding and slipping cases
Complete gear case rebuilds, bench-torn and reassembled to spec
Gear cases punish sloppy work. Wrong shimming, missed bearing wear, or a skipped pressure test comes back as a comeback failure within weeks, which is why so many general mechanics send gearbox work away. Island Marine Repair keeps it in-house. Cody, our certified marine technician, has rebuilt and resealed SWFL gear cases for 15+ years, and the boat sits in fishing-line-rich, sandbar-adjacent water down here, so the work never runs out. More about us on our About Us page.
Boaters bring us gearboxes after grinding noises, after milky drains, and sometimes after another shop's rebuild let go. The reviews describe the same experience each time: a clear diagnosis, a fair written quote, and a gear case that shifts like new and stays that way.
Line-cut seal recoveries, full lower unit rebuilds, and the before-and-after oil photos that tell the whole story.
Boating in Southwest Florida is a year-round thing. No off-season, no winter layup, no real break. And that means our shop floor and our service…
Southwest Florida boating is incredible—but it also comes with challenges. Saltwater corrosion, shallow sandbars, unexpected mechanical failures, and the difficulty of getting boats to repair…
Some of the most satisfying work we do isn’t dramatic breakdown rescues — it’s the steady, careful maintenance and smart upgrades that keep good boats…
Canal boats meet fishing line daily, and line-cut gear case seals are one of our most frequent Cape Coral repairs: drained, pressure tested and resealed at the lift before water does bearing damage.
Dockside gearbox diagnosis and seal work across the river, drains read and pressure tests run right at the lift, with river-debris strikes and prop-shaft line wraps leading the call log.
Lower unit service for Naples' offshore fleet, where a slipping clutch dog forty miles out is not an acceptable discovery and pre-season pressure tests are cheap certainty.
Gear case and outdrive work for Charlotte Harbor boats, sterndrives included: bellows, seals and gear service for the cruising fleet that lives on its drivetrain.
Island gearbox calls handled on-site, including the sandbar souvenirs Sanibel's shallow flats hand out: bent props, nicked skegs and the seal damage that follows.
Full gear case service dispatched to the outer islands, pressure tester aboard, because milky oil discovered on Captiva deserves the same-week response it would get anywhere.
Matlacha's hard-fishing fleet keeps propshaft seals in steady demand, and we repair them at the dock: line cuts caught early stay seal jobs instead of becoming rebuilds.
Gearbox diagnosis and lube service for the Estero Bay communities, where skinny grass flats and oyster edges write the wear schedule and annual drains tell the truth.
Lower unit repairs along the Imperial River and Bonita's gulf-access canals, with pass-running boats getting the prop, seal and bearing attention their duty cycle earns.
Lemon Bay boats get complete gearbox service, mobile, without the run to Fort Myers: Stump Pass sand and shallow-bay running kept honest by scheduled service at your dock.
Dockside diagnosis today, honest quote in writing, repair done to spec.
