Know which drive you're standing behind

The single most common MerCruiser quoting mistake is assuming all sterndrive impeller jobs are the same. They are not:

• Alpha (One/Gen II): the raw water pump lives inside the drive, driven by the driveshaft. Replacing the impeller means dropping or pulling the upper portion of the work into a drive-off job in many cases — more labor, and while you're in there you inspect bellows, gimbal, and u-joints.
• Bravo (I/II/III): the raw water pump is on the engine (belt- or crank-driven sea pump). Impeller access is from inside the engine bay — much faster, often under an hour.

Confirm the drive model from the serial tag, not the owner's memory.

Alpha procedure overview

1. Battery disconnected, drive supported, boat on trailer or stands.
2. Remove the drive per the service manual (shift linkage discipline matters — note positions).
3. The pump sits atop the lower unit: remove housing, impeller, wear face, and gaskets; replace as a complete kit.
4. Inspect the driveshaft, u-joints, gimbal bearing, and all bellows while the drive is off — this is the cheapest moment they will ever be inspected. Tell the customer what you found either way.
5. Reinstall with alignment checked per the manual.

Bravo procedure overview

1. Battery disconnected, seacock closed or muffs off.
2. Remove the sea pump cover or the pump body, note impeller rotation, swap the impeller and O-rings/gaskets as a kit.
3. Lube the impeller for the dry-start moment, rotate into place respecting vane direction.
4. Reprime: Bravo systems can airlock — fill the pump/hose per the manual before the first start and confirm water flow immediately.

Common mistakes

• Quoting a Bravo price for an Alpha job
• Skipping the bellows inspection with an Alpha drive already off — malpractice-level waste
• Losing impeller vane fragments upstream in the cooling system after a failure; find them or meet the overheat later
• Dry-running to "test" before the pump is primed

When to walk away

An Alpha with a rusted gimbal bearing, wasted u-joints, and cracked bellows discovered mid-job needs a re-quote conversation before reassembly — never quietly reassemble known-bad parts.

Safety: drives are heavy — use a drive dolly or a second set of hands. Key out, battery off before rotating anything by hand.