Mercury – U-Joint Bellows Assembly | Sterndrive Driveline Protection | 86840A05

Overview

This U-joint bellows is the flexible sleeve that keeps water out of the driveline area on Bravo, Blackhawk, and Vazer drives. When the old one dries out or starts cracking, it doesn’t take much for water to find its way in, and that can turn into an expensive mess pretty quickly. Swapping in a fresh OEM bellows is one of those jobs that feels small but makes a big difference. The kit comes with the clamps you need, and the install is pretty manageable with everyday tools.

Key Features

 • Ribbed Composite Bellows – Flexible design that seals the bell housing from water intrusion.
 • Clamps Included – Bands for both ends are supplied in the kit.
 • Fresh Sealing Parts – Comes with a new element and O-ring.
 • Built for Movement – Holds up to vibration and engine flex without tearing.
 • Marine-Friendly Materials – Stands up to moisture, heat, and long-term exposure.

Engine & Boat Compatibility

 • MerCruiser Bravo sterndrives (1991+)
 • MerCruiser Blackhawk sterndrives
 • MerCruiser Vazer sterndrives
 • Standard U-joint bell housing setups

Performance & Practical Benefits

A new bellows keeps the driveline dry, which goes a long way toward preventing corrosion inside the housing. If your old bellows were getting stiff, you’ll usually notice smoother movement once everything’s sealed back up. It’s also one less thing to worry about when you’re running in rougher water or trimming the drive up and down. Simple part, big payoff.

Why Buy OEM

Mercury molds these bellows to match the exact shape and groove layout on their drives, so they seat properly without stretching or fighting the fit. The material holds up far better than bargain bellows when it comes to heat, flex, and vibration. Using OEM here simply avoids the “do it twice” scenario.

FAQ

Q1: How do I know my bellows need replacing?
Cracks, stiffness, water in the bell housing, or rusty U-joints are all warning signs.

Q2: Do I need any special tools?
Not really—basic hand tools work. A bellows expander just makes it easier.

Q3: Does it handle saltwater okay?
Yes, just give the area a rinse now and then to help it last longer.

Q4: Any install tips?
Make sure the bellows lip is fully seated in its groove before tightening the clamps.

Q5: What happens if I ignore a worn bellows?
Water gets in, and the U-joints or gimbal bearings end up paying the price—usually not cheap.

• Supersessions
  86840A3, 8M0062406, 8M0062406