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OBR replacement gearcase for select Mercury 75, 90 and 115 HP four-cylinder four-stroke outboards. This product family covers standard, Command Thrust, 115 Pro XS, and 115 Pro XS Command Thrust configurations, with both 20-inch L and 25-inch XL shaft options.
Standard 75/90/115 and 115 Pro XS configurations use the listed 2.07:1 gear ratio. Command Thrust and Pro XS Command Thrust configurations use 2.38:1. Each application is available as either a new or remanufactured OBR gearcase under its own ME-G4 SKU.
Fitment must be determined from the engine serial number, model number, existing gearcase family, shaft length, and gear ratio. Horsepower and model year alone are not sufficient. Product-specific supplier listings currently identify standard and Command Thrust applications through 2023 and Pro XS applications through 2023. Any 2024 order must be confirmed in writing before shipment.
OBR states that gearcase assemblies ship without lubricant. The correct manufacturer-specified gear oil must be added before operation, and OBR’s break-in and shift-adjustment instructions must be followed. New and remanufactured OBR gearcases are covered by OBR’s published two-year limited warranty, subject to its inspection, installation, and usage requirements.
| Specification | Mercury 75–115 HP 4-Stroke Lower Unit | Pro XS & Command Thrust |
|---|---|
| Manufacturer / Brand | OBR Parts |
| Compatible Engine Make | Mercury |
| Engine Architecture | Four-cylinder four-stroke |
| Standard and Command Thrust Fitment | 75 HP, 90 HP and 115 HP applications listed for 2014–2023 |
| Pro XS Fitment | 115 HP Pro XS and Pro XS Command Thrust applications listed for 2016–2023 |
| 2024 Applications | VERIFY BEFORE PUBLISHING — current product-specific supplier listings end at 2023 |
| Available Configurations | Standard, Command Thrust, 115 Pro XS and 115 Pro XS Command Thrust |
| Shaft Lengths | 20-inch L and 25-inch XL |
| Standard / Pro XS Gear Ratio | 2.07:1 |
| Command Thrust Gear Ratio | 2.38:1 |
| Condition Options | New and remanufactured |
| SKU Families | ME-G4-07D, ME-G4-07F, ME-G4-20, ME-G4-21, ME-G4-25, ME-G4-26, ME-G4-30 and ME-G4-31 |
| Rotation | VERIFY BEFORE PUBLISHING — no counter-rotation SKU is identified among the 16 current variants |
| Warranty | OBR two-year limited warranty for new and remanufactured gearcases |
| Gear Oil | Not installed for shipment; fill with the engine manufacturer's specified gear lubricant before operation |
| Fitment Verification | Engine serial number, model number, gearcase family, shaft length and gear ratio must be confirmed |
| Core Charge | VERIFY BEFORE PUBLISHING — confirm whether a refundable core deposit is included or charged for each SKU |
This OBR Mercury 75–115 HP four-stroke lower-unit family provides new and remanufactured replacement gearcases for select Mercury 75 HP, 90 HP and 115 HP outboards. Available applications include standard Mercury lower units, Mercury Command Thrust lower units, Mercury 115 Pro XS lower units and Pro XS Command Thrust configurations.
Choose between a 20-inch L or 25-inch XL shaft. Standard and non-Command-Thrust Pro XS configurations use the listed 2.07:1 gear ratio, while Command Thrust configurations use 2.38:1. Every shaft length, gearcase type and condition has a separate ME-G4 SKU.
Before ordering, confirm your Mercury engine serial number, model number, existing gearcase configuration, shaft length and gear ratio. Horsepower and model year alone are not enough to guarantee fitment. Current product-specific supplier listings cover 2014–2023 standard and Command Thrust applications and 2016–2023 Pro XS applications. A 2024 engine requires written compatibility confirmation before purchase.
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The product details made it simple to verify that this gearcase was the exact match for my 2019 Mercury 115 HP Pro XS. The 2.07:1 gear ratio, 20-inch shaft length, and high-performance housing specs aligned perfectly. Double-check your gear ratio before ordering.
I appreciated how clearly the Command Thrust options were separated from standard gearcase models. The larger 4.9-inch torpedo housing and 2.38:1 gear ratio made a huge difference on my heavy pontoon boat. Fitment support was very helpful.
The drive shaft splines and mounting bolt pattern lined up without issue on my 2017 Mercury 75 HP 4-stroke. The unit was well-packaged in foam padding. Shifts cleanly and runs quiet after completing the break-in period.
Matching the engine serial number and gear ratio made ordering straightforward. The lower unit performs well on the water, though removing the protective transport frame and unboxing required extra effort during setup.
Replaced a worn lower unit on my 115 HP Command Thrust outboard. The product listing detailed shaft length and gear ratio parameters clearly, preventing any fitment mistakes. Performance has been solid since day one.
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