Match your lower unit by three things: your engine's HP range, shaft length (L, XL, or XXL), and gear ratio. Check your current gearcase tag or your engine's model number to confirm these specs — most Mercury outboards from the same HP range share a common lower unit, but shaft length and gear ratio can vary by model year.

A new lower unit is built with all-new components, while a remanufactured unit is rebuilt from a core using OEM-spec parts and tested to the same performance standard — both come with warranty coverage. Remanufactured units offer the same reliability at a lower cost, making them a popular choice for budget-conscious repairs.

A higher gear ratio (like 2.33:1) gives more low-end torque, ideal for pushing heavier boats or larger props. A lower ratio (like 1.62:1 or 1.75:1) favors top-end speed, common on high-horsepower V6 and Verado engines. Always match your replacement to your engine's original ratio unless you're intentionally re-gearing for a different prop setup.

Common symptoms include gear lube that looks milky or metallic, humming or grinding noise while underway, difficulty shifting, or a sudden loss of power at the prop. If you notice any of these, it's best to replace the lower unit before saltwater intrusion causes further internal damage.

Yes — we stock counter rotation gearcases for Mercury twin-engine configurations, engineered to keep both engines thrust-balanced and synchronized. These are commonly needed for the port-side engine in a dual-outboard setup.

Yes, saltwater is one of the leading causes of gearcase failure — it corrodes internal bearings, seals, and housing over time, especially if the anodes aren't replaced regularly. Rinsing your outboard after every saltwater trip and inspecting the gear lube for water contamination can significantly extend your lower unit's lifespan.

Yes, every Mercury lower unit sold here — new or remanufactured — includes warranty coverage, so you can install with confidence.

A pressure test checks for internal seal or gasket leaks before you fill the gearcase with oil. Using a pressure tester attached to the vent screw hole, pump it to about 12–15 PSI and watch the gauge for 5–10 minutes — if the pressure holds steady, the seals are intact; if it drops, there's a leak that needs addressing before installation. We recommend doing this on every new or remanufactured lower unit before it's mounted.

Yes, Mercury recommends changing gear lube at least once a season, or every 100 hours of run time — whichever comes first. Saltwater use, heavy towing, or high-RPM operation can shorten that interval. Always check the drained oil for a milky color or metal flakes, both signs the lower unit needs inspection.

The most frequent installation issues are misaligned shift shaft splines, improper torque on the mounting bolts, and forgetting to pressure test before filling with gear lube. Taking time to align the driveshaft and shift shaft correctly before final tightening prevents most post-install shifting or leak problems.