Bellows are the folded rubber boots that seal the gap between the transom assembly and the drive. There are usually three: the exhaust bellows, the driveshaft bellows and the shift cable bellows. Rubber dries out and cracks with age and UV, and a split bellows lets water into the boat and soaks the gimbal bearing. Brad replaces bellows sets on MerCruiser, OMC and Volvo Penta drives and checks the gimbal bearing behind them while the drive is off.
Signs the bellows are done
- Water in the bilge that shows up only when the boat is in gear or underway
- Visible cracks or dry rot in the folds of the rubber boots
- A gimbal bearing that has started to growl from getting wet
- A soft or collapsing exhaust bellows you can see sagging
- Water pushing back up through the drive during a hose test
- Bellows past four to five years old that have never been changed
What Brad checks with the drive off
- Inspect all three bellows for cracks, rot and clamp condition
- Check the gimbal bearing behind the driveshaft bellows
- Look at the u-joints and driveshaft while access is open
- Verify the shift cable and bellows for binding and wear
- Check the transom plate and gimbal housing for corrosion
- Reseal and reclamp so the new bellows seat without leaks
The fix and what to expect
With the drive pulled, Brad replaces the exhaust, driveshaft and shift bellows as a set, new clamps included, and seats them with proper adhesive where the design calls for it. The gimbal bearing gets inspected and greased or replaced while it is exposed, since that is the cheap time to do it. Then the drive goes back on and gets a water test. Bellows are a maintenance item, not a repair you do once. Fresh rubber every four to five seasons keeps water out and the bearing dry.
Do all three bellows together, not one at a time
People sometimes want to change only the boot that split. The problem is that all three bellows are the same age and the same rubber, and pulling the drive is most of the labor. Doing one now and another next year means paying the drive-off labor twice. On MerCruiser Alpha drives the exhaust bellows takes the most heat and usually cracks first, but the driveshaft bellows is the one that drowns the gimbal bearing, so Brad does the full set every time. It is the difference between a maintenance visit and a repeat repair.