MerCruiser Alpha and Bravo drives use three bellows between the transom and the drive: exhaust, driveshaft and shift. The rubber dries and cracks with age, and a split lets water into the bilge and soaks the gimbal bearing. Brad replaces the full MerCruiser bellows set, new clamps included, and checks the gimbal bearing behind them while the drive is off. Doing all three together is the only way that makes sense given the drive-off labor.
Signs MerCruiser bellows are done
- Bilge water that appears only when the boat is in gear or moving
- Cracks or dry rot visible in the folds of the rubber
- A gimbal bearing starting to growl from getting wet
- A sagging or collapsing exhaust bellows
- Water pushing back through the drive on a hose test
- Bellows over four to five years old never yet replaced
What Brad checks with a MerCruiser drive off
- Inspect exhaust, driveshaft and shift bellows for cracks and rot
- Check the gimbal bearing behind the driveshaft bellows
- Look at the u-joints and driveshaft while access is open
- Verify the shift cable and its bellows for binding
- Check the gimbal housing and transom seal for corrosion
- Seat the exhaust bellows with proper adhesive on Alpha drives
The fix and what to expect
With the drive pulled, Brad replaces the exhaust, driveshaft and shift bellows as a set with new clamps, seating the exhaust bellows with adhesive where the Alpha design requires it. The gimbal bearing gets greased or replaced while it is exposed. Then the drive goes back and gets a water test. Fresh MerCruiser bellows every four to five seasons keep water out and the bearing dry, and doing the set at once means paying the drive-off labor only once.
Alpha exhaust bellows takes the heat, driveshaft takes the blame
On a MerCruiser Alpha the exhaust bellows carries hot exhaust and is usually the first to harden and crack, so it looks like the problem. But the bellows that actually causes the expensive damage is the driveshaft bellows, because when it splits, lake water washes straight over the gimbal bearing and kills it. That is why Brad never does just the one that looks bad. He replaces all three, and on the Alpha he glues the exhaust bellows properly rather than only clamping it, which is a common shortcut that leaks.