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Required for fitment review to confirm compatibility.
The OBR Mercury/Mariner 75–90 HP Four-Stroke Lower Unit is a precision-built new or remanufactured replacement gearcase designed specifically for selected four-cylinder Mercury and Mariner 75 HP and 90 HP four-stroke outboards produced from 2000 through 2006. Engineered to restore peak propulsion and reliable power transfer, this heavy-duty gearcase provides a dependable, high-quality alternative for marine servicing and overhaul projects.
This application is structured across three distinct model-year groups to match specific internal configurations. The 2000–2002 and 2003 model-year units are built around the short shift-rod arrangement. The 2004–2006 model-year units feature the long shift-rod arrangement and are offered in both 20-inch (L) and 25-inch (XL) driveshaft lengths to accommodate varying transom setups.
Horsepower and model year alone cannot confirm fitment. Precise verification requires checking the complete engine model and serial number, current OEM gearcase part number, shift-rod configuration, driveshaft length, gear ratio, and rotation prior to variant selection. These gearcases are OBR aftermarket replacement units engineered for compatibility with Mercury/Mariner engines and are not represented as Mercury-manufactured or SEI lower units.
2000–2002 | Short Shift Rod | 20-inch L
2003 Only | Short Shift Rod | 20-inch L
2004–2006 | Long Shift Rod | 20-inch L
2004–2006 | Long Shift Rod | 25-inch XL
Do not order using horsepower and model year alone.
Your selected SKU and submitted engine information will be reviewed against the selected model-year group, shift-rod configuration, and driveshaft length. Mariners Warehouse may contact you if the submitted information conflicts with the selected option. Ensure the engine idle RPM is set to manufacturer specifications, verify shift cable adjustment for full shift travel, inspect the water pump impeller and drain plug seals, and apply marine grease to the driveshaft splines before mounting. Gearcases must always be tested under water load rather than on a water hose.
OBR gearcase assemblies ship without oil. Fill the unit strictly from the lower drain hole until lubricant flows steadily out of the upper vent hole, using the gear oil required by the engine manufacturer before operation. Correct idle speed and shift adjustment are essential. After the first 10 hours of operation, inspect the gear lube for metal shavings or water intrusion.
During the first 10 operating hours, avoid full-throttle starts. Shift into forward at least 10 times using moderate engine speed, and do not operate at one constant speed for extended periods. Do not exceed 75 percent throttle during the first five hours. During the next five hours, do not maintain full throttle for extended periods.
| Specification | Mercury Outboard Lower Unit | 75–90 HP | 4-Cylinder 4-Stroke |
|---|---|
| Manufacturer | OBR |
| Compatible Engine Brand | Mercury / Mariner |
| Product Family | Selected 75–90 HP four-cylinder four-stroke replacement lower units |
| Horsepower | 75 HP and 90 HP |
| Model Years | 2000–2006, divided by shift-rod configuration |
| Conditions | New and remanufactured |
| 2000–2002 Configuration | Short shift rod; 20-inch L; ME-G4-08-R or ME-G4-08-N |
| 2003 Configuration | Short shift rod; 20-inch L; ME-G4-08A-R or ME-G4-08A-N |
| 2004–2006 L-Shaft Configuration | Long shift rod; 20-inch L; ME-G4-09-R or ME-G4-09-N |
| 2004–2006 XL-Shaft Configuration | Long shift rod; 25-inch XL; ME-G4-09A-R or ME-G4-09A-N |
| 2000–2002 OEM References | 9011G67 and 9011J2 |
| 2003 OEM Reference | 9011J2 |
| 2004–2006 20-inch OEM Reference | 888845T03 |
| 2004–2006 25-inch OEM Reference | 888845T04 |
| Serial Number | Required for fitment review; OBR’s public SKU pages do not publish complete engine serial ranges |
| Gear Ratio, Rotation and Splines | Must be verified against the existing application before ordering |
| Major Exclusions | Do not use for BigFoot/Command Thrust, Optimax/DFI, 115 HP or later-generation applications without SKU-level confirmation |
| Shipping Preparation | Ships without gear oil; fill with the manufacturer-required lubricant before operation |
| Warranty | Two-year OBR limited warranty; written terms and exclusions apply |
Choosing the correct configuration requires more than matching 75 or 90 horsepower. These OBR Mercury four-stroke lower units are divided by model-year group, shift-rod configuration and driveshaft length.
The verified 2000–2002 and 2003 applications both use a short shift-rod configuration, but they have separate OBR SKU groups. Do not treat the 2003 unit as interchangeable with the earlier version without checking the engine serial number and existing OEM gearcase number.
The 2004–2006 applications use a long shift-rod configuration. These later units are available with either a 20-inch L driveshaft or a 25-inch XL driveshaft.
After selecting the correct application, choose new or remanufactured condition. Condition does not replace the need to verify fitment.
Before ordering, record the complete engine model and serial number and inspect the existing unit for its OEM number. Confirm the shift-rod configuration, driveshaft length, gear ratio, rotation and spline count. If any information is uncertain, request a manual fitment review before installation.
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The product details made it easy to confirm that this 4-cylinder 4-stroke gearcase was the exact match for my 2017 Mercury 90 HP outboard. The 2.33:1 gear ratio and 20-inch shaft length specs were spot-on. Double-checking your gear ratio prior to purchasing is a must.
Ordering replacement lower units can be confusing, but Mariners Warehouse fitment advice helped me pick the right 2.07:1 configuration for my 2015 Mercury 75 HP 4-stroke. The unit arrived well-secured in molded foam without any transit damage.
The application details clearly distinguished the 25-inch XL shaft model from the standard 20-inch version. Drive shaft spline alignment and mounting studs lined up perfectly on my 4-cylinder 4-stroke engine. Smooth gear shifts right out of the box.
Matching the serial number and gear ratio made ordering simple. The lower unit performs great on the water, though removing the protective wooden transport frame required extra tools and patience. Be sure to follow the recommended oil fill procedure.
Replaced my worn-out gearcase on a 2012 Mercury 75 HP 4-stroke. The fitment warnings regarding bullet diameter and drive shaft length saved me from ordering the wrong part. After completing the break-in period, it operates smoothly.
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