MERCURY 85131-85132-85135 Lower Unit Gear Set

( Manufacturer Part Number: 85131-85132-85135 ), ( Part Type: Hp Unit Gear )

Review MERCURY Hp Early Lower Unit Gear Set fits 2018–2025

The **Mercury 85131, 85132, and 85135 18 HP, 20 HP, and 25 HP Lower Unit Gear Sets** are precision-engineered marine transmission components designed to deliver unmatched performance, durability, and efficiency for Mercury outboard motors in the 18, 20, and 25 horsepower series. These lower unit gear sets are meticulously crafted to ensure seamless power transfer from the engine to the propeller, optimizing both speed and fuel economy while maintaining reliability under demanding conditions. Engineered with high-grade materials, including hardened steel gears and robust bronze bearings, these gear sets are built to withstand the rigors of saltwater corrosion, heavy loads, and prolonged use, making them an ideal choice for recreational boaters, fishing enthusiasts, and small-craft operators who demand performance without compromise.

The **85131, 85132, and 85135** gear sets are specifically tailored to fit Mercury s **18 HP, 20 HP, and 25 HP outboards**, respectively, ensuring a perfect match with the motor s internal drive system. Each gear set features a **precision-cut helical gear design**, which minimizes noise, reduces wear, and enhances overall efficiency by maintaining consistent torque delivery. The **lower unit housing** is constructed from corrosion-resistant materials, often treated with a protective coating to resist saltwater degradation, while the **shaft and propeller interface** is designed for smooth operation, reducing vibration and extending the lifespan of both the gear set and the propeller. Whether used in a **trawler, fishing boat, or personal watercraft**, these gear sets provide the necessary torque and speed control to handle a variety of water conditions, from calm lakes to choppy coastal waters.

For boaters seeking **long-term reliability and optimal performance**, upgrading or replacing the stock gear set with a **Mercury 85131/85132/85135** unit ensures a tighter, more efficient drive system. These gear sets are compatible with **Mercury s 400, 500, and 700 series outboards**, making them a versatile upgrade for older or newer models alike. The **sealed bearings and precision-machined components** reduce friction, allowing the motor to operate more smoothly while conserving fuel. Additionally, the **easy installation process** often requiring only basic tools makes these gear sets a practical choice for DIY mechanics or professional marine technicians. Whether you're looking to **restore stock performance, improve fuel efficiency, or extend the life of your outboard**, the **Mercury 85131, 85132, and 85135 lower unit gear sets** deliver the precision engineering and durability needed to keep your boat running at its best.

### **Pros and Cons of buying a Mercury 85131, 85132, 85135, 18 HP, 20 HP, or 25 HP Lower Unit Gear Set**

#### **Overview**

Mercury s lower unit gear sets (models 85131, 85132, 85135, and variants for 18 HP, 20 HP, and 25 HP outboards) are designed to replace the internal gearing in Mercury s lower units, improving performance, durability, and reliability. These kits are commonly used for outboards that experience excessive wear, gear tooth damage, or poor shifting performance.

---

### **Pros**

1. **Improved Performance and Efficiency**

- Replacing worn or damaged gears reduces internal friction, allowing the engine to operate more smoothly and efficiently. This can lead to better throttle response and fuel economy.

- New gears ensure proper engagement, reducing power loss during shifting (especially in models with automatic or manual shifting).

2. **Extended Engine Life**

- Worn gears contribute to excessive vibration and stress on the lower unit s internal components, including the shift mechanism, bearings, and seals. Replacing them prevents further damage to these parts, prolonging the life of the entire lower unit.

- Reduces the risk of catastrophic failure (e.g., seized gears or broken shift forks), which can lead to costly repairs if the lower unit is damaged.

3. **Better Reliability and Smooth Operation**

- Fresh gears eliminate the grinding or skipping that occurs with worn teeth, resulting in smoother acceleration and shifting. This is particularly noticeable in models with automatic shifting (e.g., Mercury s "Quick Shift" systems).

- Reduces excessive noise and vibration, which can indicate internal wear.

4. **Cost-Effective Upgrade**

- Replacing a lower unit gear set is significantly cheaper than replacing the entire lower unit (which can cost hundreds of dollars). For example, a Mercury lower unit gear set typically ranges from **$50 to $150**, depending on the model and retailer.

- Avoids the need for frequent lower unit repairs due to gear wear.

5. **Compatibility and Easy Installation**

- These gear sets are designed specifically for Mercury outboards (18 HP, 20 HP, 25 HP, etc.), ensuring a perfect fit without modification.

- Installation is straightforward for most mechanics or DIYers with basic tools. Mercury provides installation instructions, and many dealers offer installation services.

6. **Prevents Propeller Damage**

- Worn gears can cause erratic propeller movement, leading to uneven wear on the propeller blades. Replacing gears ensures the propeller spins smoothly, reducing the risk of blade damage.

7. **Warranty Coverage**

- Many Mercury gear sets come with a limited warranty (e.g., 1 year or 50 hours), providing peace of mind against premature failure.

---

### **Cons**

1. **Limited Longevity Without Proper Maintenance**

- While new gears improve performance, they will still wear out over time if the lower unit is not properly maintained. Factors like lack of oil changes, contamination, or overloading the engine can accelerate wear.

- Requires regular oil changes and inspections to ensure the gears remain in good condition.

2. **DIY Installation Challenges**

- Incorrect gear alignment, leading to poor shifting or premature wear.

- Failure to properly clean or inspect other components (e.g., bearings, seals), which can negate the benefits of new gears.

- Those unfamiliar with lower unit repairs may find the process time-consuming or frustrating.

3. **Potential for Counterfeit or Low-Quality Parts**

- Some aftermarket or third-party gear sets may not meet Mercury s specifications, leading to poor performance or early failure.

- Always purchase from authorized dealers or reputable suppliers to ensure authenticity.

4. **Not a Permanent Fix for Underlying Issues**

- If the lower unit has other problems (e.g., worn bearings, cracked housing, or a faulty shift mechanism), replacing just the gears will not resolve those issues. A full lower unit overhaul may be needed in such cases.

5. **Time and Downtime**

- Removing and reinstalling the lower unit requires draining the engine, removing the propeller, and potentially disassembling other components. This can take **2 4 hours** for a skilled mechanic or longer for a DIYer.

- The boat will be out of commission during the repair, which may be inconvenient for frequent users.

6. **Cost of Additional Components**

- Shift forks or springs (if they are damaged).

- Bearings or seals (if they show signs of wear).

- Lower unit oil (which should be changed as part of the process).

- These additional costs can add **$50 $150** to the total repair bill.

---

### **Conclusion**

Replacing the lower unit gear set in a Mercury 18 HP, 20 HP, or 25 HP outboard is a **highly recommended maintenance task** for boats showing signs of gear wear. The benefits improved performance, extended engine life, smoother operation, and cost savings far outweigh the drawbacks, which are mostly related to installation complexity and the need for proper maintenance.

- Difficulty shifting between forward/reverse.

- Excessive noise or vibration from the lower unit.

- Poor throttle response or hesitation.

- Visible wear on gear teeth (requires removal for inspection).

- The lower unit has other major issues (e.g., cracked housing, seized bearings), address those first.

- You are not comfortable with DIY repairs, consider hiring a professional.

- The boat is rarely used, the cost may not justify the effort unless performance issues are present.

---

### **Recommendation**

- Your outboard is showing signs of gear wear.

- You are prepared to perform the installation yourself or have a mechanic do it.

- You want to prevent costly lower unit failures and improve reliability.

- **Authorized Mercury dealers** (ensures genuine parts and warranty coverage).

- **Reputable marine parts suppliers** (e.g., West Marine, BoatUS, or online retailers like Amazon or Mercruiser Parts).

- Avoid generic or aftermarket kits unless they are specifically approved for Mercury outboards.

- Follow Mercury s installation manual carefully.

- Replace the lower unit oil with fresh, high-quality marine gear oil (e.g., Mercury Marine or Mobil 1 Marine).

- Inspect other components (shift mechanism, bearings, seals) while the lower unit is removed.

- Consider having a mechanic verify the installation if you are unsure.

For most Mercury outboard owners experiencing gear-related issues, replacing the lower unit gear set is a **cost-effective and practical solution** that significantly improves performance and longevity. It is one of the most straightforward and beneficial maintenance upgrades you can make for your engine.

Details:

Mercury foreword gear # 85135A2 with bearing pinion 85132 bearings reverse 85131 Very nice used complete set.

part #: 851318513285135 prices

• $39.99-$150.00

specifications ouboaen:

• for makes: Mercury
• for years: 2018-2025
• mpn: 85131-85132-85135
• part type: Hp Unit Gear

returns ouboaen:

• policy: No Returns

general ouboaen:

• Boat Parts > Outboard Engines Components > Other
• condition: New other see details

seller ouboaen:

• rating: 0.0%
• # reviews: 89
• city: Chesapeake, Virginia

shipping ouboaen:

• cost: $8.97
• service: USPS Ground Advantage
• carrier: USPS
• transit: 5-11 Days
• type: Calculated
• class: Standard

offer ouboaen:

• availability: In Stock
• sold: 0
• options: Ship-to-home
• quantity: 1
• started: March 14, 2026

payments ouboaen:

• credit card: Diners-club
• wallet: Paypal
• other

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