Shift Shaft Bushing Assembly – Fits MerCruiser Alpha One Gen II (Replaces 23-815921A17, 23-815921A21)
Shift Shaft Bushing Assembly – Fits MerCruiser Alpha One Gen II (Replaces 23-815921A17, 23-815921A21) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Shift Shaft Bushing Assembly – Fits MerCruiser Alpha One Gen II (Re...
Product Details
This high-quality Shift Shaft Bushing Assembly is designed specifically for MerCruiser Alpha One Generation II stern drives manufactured from 1991 to 1995. It is a crucial component for ensuring smooth shifting and sealing the lower unit, fitting drives with serial numbers ranging from 0D469859 to 0K999999.
The assembly is a direct replacement for Mercury Marine part numbers 23-815921A17 and 23-815921A21. It also serves as an aftermarket interchange for GLM 21015, Mallory 9-76136, and Sierra 18-2353, offering a reliable alternative to OEM parts.
- Installation Location: Mounts on the lower unit (stern drive).
- Complete Assembly: This is a five-piece kit that includes all necessary housing pieces, seals, and a zip tie for installation.
- Durable Construction: Made from high-quality plastic/polymer materials to withstand the marine environment.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number | Notes |
|---|---|---|
| Mercury Marine | 23-815921A21 | Current OEM part number. Supersedes previous versions. |
| Mercury Marine | 23-815921A17 | Superseded by 23-815921A21 |
| Mercury Marine | 23-815921A10 | Superseded by 23-815921A21 |
| Mercury Marine | 23-815921A8 | Superseded by 23-815921A21 |
| Mercury Marine | 23-815921A6 | Superseded by 23-815921A21 |
| Mercury Marine | 23-815921A2 | Superseded by 23-815921A21 |
| GLM | 21015 | Aftermarket Replacement |
| Mallory | 9-76136 | Aftermarket Replacement |
| Sierra | 18-2353 | Aftermarket Replacement |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure accurate fitment.
| Brand | Model | Years | OEM Part No. | Notes |
|---|---|---|---|---|
| MerCruiser | Alpha One Gen II | 1991–1995 | 23-815921A17 / 23-815921A21 | Fits serial numbers 0D469859–0K999999. |
Technical Specs
- Product Type
- Shift Shaft Bushing Assembly
- Installation Location
- Lower Unit / Stern Drive
- Housing Material
- Plastic/Polymer
- Dimensions
- Height: 5.0; Width: 14.5; Length: 23.0;
- Assembly Contents
- Five-piece assembly includes housing pieces, seals, and zip tie.
What’s in the Box
-
1 x Shift Shaft Bushing Assembly (5-Piece Kit), including:
- Housing pieces
- Seals
- Zip tie
Installation Notes
- Disconnect the boat's battery and ensure the engine is completely off.
- Drain the gear lube from the stern drive's lower unit.
- Following the manufacturer's service manual, carefully remove the lower unit from the upper housing.
- Locate the existing shift shaft bushing assembly on the lower unit.
- Remove the old bushing, seals, and any retaining clips or hardware.
- Thoroughly clean the installation area to remove any old sealant, debris, or corrosion.
- Install the new seals and bushing components from the kit, ensuring they are properly seated.
- Reinstall the lower unit, carefully aligning the shift shaft.
- Refill the gear case with the manufacturer-specified gear lube to the correct level.
- Reconnect the battery and test shifter operation with the engine off to confirm smooth engagement.
- Always refer to your official MerCruiser service manual for detailed procedures and torque specifications.
Troubleshooting & FAQ
How do I know if this bushing fits my MerCruiser Alpha One?
This assembly is specifically for Alpha One Generation II drives made between 1991 and 1995. It is critical to confirm your drive's serial number falls within the range of 0D469859 to 0K999999, as there are variations between model years.
The new part looks different from my old one. Is it correct?
It is common for updated OEM parts and aftermarket replacements to have slight visual differences from the original component due to design improvements or manufacturing updates. As long as your model and serial number match the compatibility list, it is the correct functional equivalent.
What are the signs of a failing shift shaft bushing?
Common symptoms include difficulty shifting between neutral, forward, and reverse; a shifter that feels unusually stiff or loose; grinding noises during gear changes; or a water leak observed around the shift shaft area of the drive.
Does this kit include everything I need for installation?
This five-piece kit includes the main housing components, seals, and a zip tie. You will still need basic hand tools and the appropriate gear lube for your drive. We always recommend consulting a service manual for detailed instructions.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility. All parts are batch-inspected for quality and consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free for most orders, with expedited options available at checkout where applicable.
Warranty & returns
This product is covered by a 1-year warranty against manufacturing defects under normal use. If any issues arise, please contact our support team with your order details. Returns are accepted within our standard window for unused parts in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Always verify images and specifications against your original part before purchasing. If anything differs—even if your model appears compatible—do not install the part.
- This is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
- Professional installation is highly recommended for safety, proper function, and to prevent damage to your marine engine.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with an average transit time of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.
Payment & Security
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