Mercury MerCruiser Quicksilver Alpha Upper Gear Set 18411A2 – 22/20T, 1.50 / 1.47 Ratio
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Overview
Part Number: 18411A2 (service format: 43-18411A2)
Brand: Mercury / Quicksilver
Official Product Type: Upper Gear Set
Supersedes: 59832A2
Related Heavy-Duty Version: 18411A4
Tooth Count: 22/20 teeth
Nominal Ratio: 1.50:1 (effective: 1.47:1)
GTIN: 745061123625
System: Upper Driveshaft Housing — Upper Gear Set
The Mercury Quicksilver 18411A2 is a genuine OEM matched upper gear set for Alpha-family MerCruiser sterndrives. It installs in the upper driveshaft housing as the matched drive-and-driven gear pair, transferring power from the engine driveshaft down through the upper unit. Because gear sets are matched pairs, both gears are replaced together — using unmatched gears leads to poor tooth contact, noise, and accelerated failure.
Key Features
- Genuine Mercury Marine / Quicksilver OEM matched upper gear set
- 22/20-tooth configuration — nominal 1.50:1 ratio (effective 1.47:1)
- Fits MC-I, R, MR, Alpha One, and Alpha One Gen II sterndrive upper units
- Common application range: 1971–1997, serial numbers 0K999999 and below
- Matched pair — drive and driven gears supplied together
- GTIN: 745061123625
Compatible Applications
- MerCruiser MC-I sterndrive (selected serial ranges)
- MerCruiser R sterndrive (selected serial ranges)
- MerCruiser MR sterndrive (selected serial ranges)
- MerCruiser Alpha One sterndrive (selected serial ranges, through 0K999999)
- MerCruiser Alpha One Gen II sterndrive (early production, selected serial ranges)
- Common application years: approximately 1971–1997
Serial Number Fitment Notice
The critical fitment points are the drive family, serial number, tooth count, and gear ratio. MerCruiser used several visually similar Alpha-family upper gear sets at different ratios — including 1.65, 1.84, and 1.98 — and they are not interchangeable. The 18411A2 should only be used where the Mercury parts diagram specifically calls for the 22/20-tooth 1.50 / 1.47 gear set. Always confirm by serial number and the applicable driveshaft housing parts diagram.
Dimensions & Weight
- Weight: Approx. 4.90 lb (2.22 kg)
- Packed dimensions: Approx. 18.5 cm × 12.2 cm × 11.7 cm (7.30 × 4.80 × 4.60 in)
When to Replace
Replace the upper gear set when inspection reveals pitted, chipped, or broken gear teeth; abnormal wear patterns; heat discoloration; excessive backlash; or noise originating from the upper driveshaft housing. Because these are a factory-matched pair, replacing only one worn gear is not appropriate — both gears must be replaced together to ensure proper tooth contact and longevity.
Service Interval
Inspect upper gears whenever the upper driveshaft housing is opened for resealing or rebuild service. There is no fixed mileage or hour interval for gear replacement — condition-based inspection at every major drive service is the standard practice for Alpha-family upper units of this age.
Installation Notes
- Installation requires correct bearing preload, gear shimming, and backlash setup — this is a precision rebuild procedure
- Associated components shown in Mercury diagrams for the 1.50-ratio upper assembly include bearing assemblies 35990A1 and 32573A1, washer 45810, nut 8M0214915, and shim set 36178A02
- Do not mix gears from different gear sets or ratios
- Confirm the correct ratio for your application before disassembly — the wrong ratio changes overall drive gearing and cannot be corrected by adjustment
- Refer to the Mercury MerCruiser service manual for the applicable drive family for full shimming and preload specifications
Superseded / Alternate Part Numbers
- Current: 18411A2 / 43-18411A2
- Supersedes: 59832A2
- Related heavy-duty gear set: 18411A4
- Aftermarket cross-reference: GLM 11210, Sierra 18-2201
Technical FAQ
Q: What is the difference between 18411A2 and 18411A4?
A: The 18411A4 is the heavy-duty version of the same 22/20-tooth 1.50 / 1.47 ratio gear set. It is typically used in higher-load applications. Both fit the same Alpha-family drive families, but the A4 uses heavier-duty gear material. If your drive originally specified A2, A2 is the correct OEM replacement unless you are upgrading.
Q: Can I reuse one gear and just replace the worn one?
A: No. Upper gear sets are matched pairs. Mixing a new gear with a worn gear leads to uneven tooth contact, noise, and premature failure of the new gear. Always replace both gears as a set.
Q: How do I confirm which ratio my drive uses?
A: The gear ratio is stamped on the drive itself or recorded on the original build sheet. You can also confirm by locating your drive serial number in the Mercury MerCruiser parts catalog and checking the driveshaft housing parts diagram — the diagram will identify the exact gear set by part number and ratio.
Parts Desk Insight
The most common ordering issue with Alpha upper gear sets is ratio confusion — several sets look similar but produce very different gearing results. A customer who installs the wrong ratio will notice incorrect engine RPM at wide-open throttle and potentially overstress the drivetrain. The serial number and the drive's original ratio spec are the two things worth confirming before this part ships. If the customer is unsure, the ratio is stamped on the drive housing.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.