Fit Sierra 18-2756 U-Joint Bellows - Marine Drive Shaft Protection for MerCruiser Bravo & Blackhawk Engines

Sierra 18-2756 U-Joint Bellows for MerCruiser Bravo & Blackhawk

Aftermarket replacement U-Joint Bellows designed for MerCruiser Bravo I, II, III, and Blackhawk sterndrive systems from 1988 to current. This component functions as a flexible, accordion-style protective cover, creating a watertight seal where the drive shaft passes through the transom. It protects the universal joint assembly from saltwater, debris, and corrosion.

Manufactured to meet or exceed OEM specifications, this bellows is a direct replacement for MerCruiser part numbers 86840A05, 86840A3, and 8M0062406. It is also compatible with OMC 775490, Mallory 9-72702, and GLM 89140. The accordion-style wall allows for the necessary movement of the drive unit during steering and trim operations while maintaining a secure seal.

• Fits MerCruiser Bravo and Blackhawk sterndrives (1988-Current).
• Engineered from durable rubber compounds for longevity in marine environments.
• Kit includes bellows, marine-grade stainless steel clamps, flange ring, and grounding clip for a complete installation.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM andbrands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• (1) U-Joint Bellows
• (1) Stainless Steel Clamp Kit (1041*1)
• (1) Bellows Flange Ring
• (1) Grounding Clip
• Note: This is a single item sale as pictured.

Installation Guide

Professional installation is highly recommended due to the critical function of this part. The following is a general guide and not a substitute for a factory service manual.

1. Position the sterndrive in the full down position and shift the engine into forward gear.
2. Disconnect all electrical connections to the drive unit, labeling them for reassembly.
3. Disconnect the trim rams by removing the rear trim pins.
4. Support the sterndrive's weight and remove the six mounting nuts securing it to the transom assembly.
5. Carefully withdraw the drive unit from the transom.
6. Remove the old bellows and thoroughly clean the gimbal housing and bell housing mounting surfaces of any old adhesive or corrosion.
7. Apply a suitable marine-grade adhesive sealant (such as Quicksilver Adhesive Sealant) to the new bellows' mounting surfaces.
8. Install the new bellows onto the bell housing first, ensuring the clamp faces downward. Seat the retainer ring correctly.
9. Reinstall the bell housing onto the gimbal housing, ensuring proper alignment.
10. Reinstall the sterndrive, torquing all mounting hardware to the manufacturer's specified values.
11. Reconnect trim rams and all electrical connections.
12. Conduct a pressure test or leak check to verify a watertight seal before operating the boat in water.

Troubleshooting & FAQ

How do I confirm this bellows fits my engine?
This part fits MerCruiser Bravo I, Bravo II, Bravo III, and Blackhawk sterndrives from 1988 to the present. The most reliable method is to match your old part number to the ones listed in our cross-reference table, such as OEM numbers 86840A05, 86840A3, or 8M0062406.

What are the signs of a failing U-joint bellows?
Common signs include visible cracks, tears, dry rot, or soft/gummy spots in the rubber. During an annual inspection with the drive removed, any evidence of water, moisture, or rust on the U-joints or gimbal bearing indicates the bellows has failed and must be replaced immediately.

How often should the U-joint bellows be replaced?
It should be inspected annually (or every 200 operating hours) by removing the sterndrive. As a preventive measure, we recommend replacing the bellows every 3-5 years, regardless of appearance, to prevent catastrophic failure and water intrusion into the drive system.

Does this kit include all the necessary hardware?
Yes, this kit is a complete assembly that includes the U-joint bellows, a marine-grade stainless steel clamp set, a bellows flange ring, and a grounding clip for a full replacement.

OEM vs. Aftermarket?
This listing is anreplacement 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.

How fast do you ship and how much does it cost?
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.

What is your warranty and return policy?
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 anreplacement 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.