Inspecting Your Stern Drive Bellows


The bellows are rubber boots designed to keep water out of the boat as well as critical areas of the outdrive itself.

There are three primary bellows for today's outdrives.

The U-joint Bellow:
This bellow is attached from the bell housing to the transom plate. It is designed to protect the u-joints and drive shaft that connects to the engine coupler. This bellow, when bad, can cause several problems.
When water gets into the u-joint bellow it can attack the u-joints, gimbal bearing and even work water into the outdrive itself through the input shaft seal.
Here are a few symptoms to help you determine if your u-joint bellows could be bad.
  • Water in the gear lube.
  • Water leaking into the boat.
  • Noise coming from the back of the boat.
  • Noise at the back of the boat when turning hard.
  • Oil spots under the drive when the boat is dry stored.

The Shift Bellow:
This bellow is attached from the shift cable at the drive to the transom plate.
This bellow's main purpose is to prevent water from leaking into the boat.

The Exhaust Bellow:
This bellow is attached from the bell housing to the transom plate and is designed to take the exhaust gases and water push them through the drive.
This bellow is sometimes just a tube that is only attached at one end (normally in a high performance situation).
This bellow is the least critical of all of the bellows and will not cause major damage if bad. Usually an increase in exhaust noise is the most common side affect.

Here are a few tips on checking the condition of your bellows.
  • Turn the drive from side to side and inspect all three bellows
  • U-Joint bellows should be firm. Poke around on them look for soft spots, cracks or tears.
  • Look for any signs of moisture on the bottom of the u-joint bellow.
  • With the drive full trimmed up turn hard to the left. This will give you excellent access to inspect the shift bellow.
  • Pull the outdrive to check the alignment and check for any signs of moisture in the bellows and shift cavity. This is a great time to grease u-joints and drive shaft.
  • Water in the shift cavity can cause the shift cable or linkage to bind, causing hard shifting. Also, Alpha models could experience the motor stalling when shifting.

Checking your bellows should be done annually and absolutely replaced when necessary.
Please keep in mind that bellows are rubber and deteriorate over time. We've found that bellows life expectancy is about 6 years.
With a little preventative maintenance you can keep your outdrive in perfect working order and prevent costly repairs in the future.

Article courtesy of Wholesale Marine

We hope this List assisted you in your ability to remain calm in the face of possible "on the water" problems, helping to insure many a successful boating adventure.