3855275 Lower Unit Gearcase Seal Kit for OMC Volvo Penta | JLM Marine

3855275 Lower Unit Gearcase Seal Kit for OMC Volvo Penta

This Lower Unit Gearcase Seal Kit is engineered to fit Volvo Penta SX sterndrives (through 2006) and OMC Cobra SX sterndrives (1994–1998). It provides a comprehensive sealing solution for a wide range of engine displacements, from 3.0L inline-4 configurations to 8.2L V8 powerplants, ensuring reliable lower unit performance across multiple model families.

This kit directly replaces OEM part number 3855275 and Sierra part number 18-2598, offering an aftermarket solution designed to meet original specifications for Volvo Penta and OMC Cobra applications.

• Complete lower unit seal kit for comprehensive gearcase service
• Fits both Volvo Penta SX and OMC Cobra SX sterndrive systems
• Covers engine models from 3.0L to 8.2L displacement

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

This Lower Unit Gearcase Seal Kit includes all necessary seals and gaskets required for a complete lower unit service on compatible Volvo Penta SX and OMC Cobra SX sterndrives. Verify all components against your engine's service manual before installation.

Installation Guide

1. Preparation: Disconnect the battery and ensure the boat is securely supported. Drain all gear oil from the lower unit into an approved container.
2. Lower Unit Removal: Remove the lower unit from the sterndrive following your engine's service manual procedure. This typically involves removing mounting bolts and disconnecting the shift linkage.
3. Disassembly: Carefully disassemble the lower unit gearcase, noting the position of all components. Clean all mating surfaces thoroughly to remove old sealant and debris.
4. Old Seal Removal: Remove all old seals, gaskets, and O-rings from the gearcase. Inspect housing bores and seal surfaces for scoring, corrosion, or damage.
5. Surface Preparation: Clean all seal mating surfaces with a suitable solvent and allow to dry completely. Ensure surfaces are smooth and free of pits or scratches.
6. New Seal Installation: Lubricate new seals lightly with gear oil before installation. Install seals using appropriate seal drivers to ensure even seating without damage.
7. Reassembly: Reassemble the lower unit following the reverse of disassembly, using new gaskets and seals from this kit. Apply marine-grade sealant only where specified by the manufacturer.
8. Reinstallation: Reinstall the lower unit onto the sterndrive, ensuring proper alignment of the driveshaft and shift linkage. Torque all fasteners to manufacturer specifications.
9. Gear Oil Fill: Refill the lower unit with the correct type and quantity of gear oil as specified in your service manual. Check for proper oil level at both fill and vent holes.
10. Leak Check: After installation, run the engine briefly and inspect all seal areas for leaks. Re-check gear oil level after initial operation.
11. Test Run: Perform a test run in the water, monitoring for any unusual noises, vibrations, or oil leaks. Recheck all fasteners and oil level after the first hour of operation.

Troubleshooting & FAQ

Q: How do I confirm this seal kit fits my Volvo Penta or OMC Cobra sterndrive?
A: Check the Compatible Engine Models table above for your specific engine model code and year range. This kit fits Volvo Penta SX through 2006 and OMC Cobra SX from 1994–1998. Verify your lower unit configuration matches the OEM part number 3855275 or Sierra 18-2598.

Q: What are the signs that my lower unit seals need replacement?
A: Common symptoms include gear oil leaking from the lower unit, water contamination in the gear oil (milky appearance), excessive gear noise, or difficulty shifting. If you notice any of these issues, inspect and replace seals promptly to prevent further damage.

Q: How often should I replace lower unit seals?
A: Seal replacement intervals depend on usage and conditions. Inspect seals annually or every 100 hours of operation. Replace seals if you find leaks, water intrusion, or during any major lower unit service or propeller shaft work.

Q: Can I install this kit myself or do I need a professional?
A: Lower unit seal replacement requires mechanical skill, specialized tools (seal drivers, torque wrench), and familiarity with sterndrive systems. If you lack experience with marine drive service, professional installation is strongly recommended to ensure proper sealing and prevent costly damage.

Q: What's the difference between OEM and aftermarket seal kits?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.