The MerCruiser Alpha One is the most common drive Brad re-bellows, and for good reason: its three boots, exhaust, driveshaft and shift, dry out on a predictable schedule and take the gimbal bearing with them when they crack. He replaces the full Alpha One bellows set with new clamps, glues the exhaust bellows as the design calls for, and inspects the gimbal bearing while the drive is off. Mail the drive in or drop it off locally.
Alpha One bellows symptoms
- Water in the bilge only when the drive is in gear or underway
- Dry-rotted, cracked folds in the rubber boots
- Gimbal bearing growl from water reaching it
- A soft or collapsed exhaust bellows
- Water intruding through the drive on a hose test
- Original bellows on a drive several seasons old
What Brad checks on an Alpha One re-bellows
- Inspect all three bellows for cracks, rot and clamp rust
- Check the gimbal bearing behind the driveshaft bellows
- Look over the u-joints and driveshaft splines
- Verify shift cable and bellows movement
- Check the gimbal housing and transom seal
- Glue and clamp the exhaust bellows to seat correctly
The fix and what to expect
Brad pulls the Alpha One drive, replaces exhaust, driveshaft and shift bellows as a set with new clamps, and seats the exhaust bellows with adhesive so it does not leak. The gimbal bearing gets greased or replaced while exposed. The drive is water tested before it goes back. On an Alpha this is routine maintenance that, done on schedule, keeps you from ever meeting the gimbal-bearing growl or a bilge full of lake water.
Why the Alpha One bellows job protects the bearing
The Alpha One packs its driveshaft, exhaust and shift lines close together behind the drive, and all three bellows age at the same rate in the same UV and heat. The driveshaft bellows is the critical one: it is the only thing keeping water off the gimbal bearing, and once it cracks the bearing has weeks, not seasons. Brad treats the Alpha One bellows as a set on a four to five year cycle for exactly this reason. It is cheap insurance against the far pricier chain of a drowned bearing, a chewed coupler and a wet bilge.