MerCruiser Alpha One Gen I complete standard-rotation sterndrive

Bravo One® & Bravo Three® Lowers Applications

Shop aftermarket replacement lower units for Bravo One and Bravo Three applications, including SE121, SE122 and SE128 options. Verify your drive configuration, water-pickup style and gear ratio before ordering.

Bravo One® & Bravo Three® Lowers Applications

Shop MerCruiser Bravo One and Bravo Three lower gearcase applications — lower-only units for boaters whose upper gear case is still serviceable and only the lower section needs replacing after wear or impact damage.

Find the correct Bravo One or Bravo Three lower unit by gear ratio below, backed by warranty coverage.

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  • Stern Drive Upper Unit 90-121-02 Single Water Pickup Side Intake Housing - Mariners Warehouse

    Sterndrive Upper Unit | SE 121 | 90-121-02 | Single Water Pickup SKU: SE90-121-02
    MPN: SE121-Lower-Bravo1Single

    $1,295.00
    $1,437.45
    $1,295.00
    Restore dependable stern drive power with this premium aftermarket upper drive housing engineered for high-performance sterndrive systems. This upper unit features a modern case design equipped with side water intakes only and an integrated internal oil passage to optimize thermal management and lubrication. Manufactured...
    $1,295.00
    $1,437.45
    $1,295.00
  • Stern Drive Upper Unit 90-122-02 Dual Water Pickup Side and Low Intake Housing - Mariners Warehouse

    Sterndrive Upper Unit | SE 122 | 90-122-02 | Dual Water Pickup SKU: SE90-122-02
    MPN: SE122-Lower-Bravo1Dual

    $1,295.00
    $1,437.45
    $1,295.00
    Restore maximum cooling efficiency and dependable stern drive power with this premium aftermarket upper drive housing engineered for high-performance sterndrive systems. This upper unit features an advanced case design equipped with dual water intakes (side and low water inlets) to optimize water volume and...
    $1,295.00
    $1,437.45
    $1,295.00
  • Stern Drive Lower Unit 90-128-02DA with 13/24 Tooth Count and Oil Recirculation Case - Mariners Warehouse

    Sterndrive Lower Unit | SE 128 | 90-128-02AA | Bravo 3 | 1.36/1.50 Ratio SKU: SE90-128-02AA
    MPN: SE128-Lower-Bravo3AA

    $2,245.00
    $2,491.95
    $2,245.00
    Restore maximum dual-propeller propulsion and efficiency with this premium aftermarket lower unit engineered for high-performance sterndrive systems. This lower housing features the updated modern case design integrated with a front-facing oil recirculation system to optimize thermal cooling and continuous lubrication under heavy loads. Built...
    $2,245.00
    $2,491.95
    $2,245.00
  • Stern Drive Lower Unit 90-128-02DA with 13/24 Tooth Count and Oil Recirculation Case - Mariners Warehouse

    Sterndrive Lower Unit | SE 128 | 90-128-02BA | Bravo 3 | 1.65 Ratio SKU: SE90-128-02BA
    MPN: SE128-Lower-Bravo3BA

    $2,245.00
    $2,491.95
    $2,245.00
    Restore maximum dual-propeller propulsion and efficiency with this premium aftermarket lower unit engineered for high-performance sterndrive systems. This lower housing features an updated modern case design integrated with a front-facing oil recirculation system to optimize thermal cooling and continuous lubrication under heavy loads. Built...
    $2,245.00
    $2,491.95
    $2,245.00
  • Stern Drive Lower Unit 90-128-02DA with 13/24 Tooth Count and Oil Recirculation Case - Mariners Warehouse

    SE 128 Lower Unit | 90-128-02CA | Bravo 3 | 1.81, 2.00 & 2.20 Ratio SKU: SE90-128-02CA
    MPN: SE128-Lower-Bravo3CA

    $2,245.00
    $2,491.95
    $2,245.00
    Restore maximum dual-propeller efficiency and thrust with this premium aftermarket lower unit engineered for high-performance sterndrive systems. This lower housing features the updated modern case design integrated with a front-facing oil recirculation system to optimize thermal cooling and continuous lubrication under heavy loads. Built...
    $2,245.00
    $2,491.95
    $2,245.00
  • Stern Drive Lower Unit 90-128-02DA with 13/24 Tooth Count and Oil Recirculation Case - Mariners Warehouse

    SE 128 Lower Unit | 90-128-02DA | Bravo 3 | 2.43 Ratio SKU: SE90-128-02DA
    MPN: SE128-Lower-Bravo3DA

    $2,245.00
    $2,491.95
    $2,245.00
    Restore maximum dual-propeller efficiency and low-end thrust with this premium aftermarket lower unit engineered for high-performance sterndrive systems. This lower housing features an updated modern case design integrated with a front-facing oil recirculation system to optimize thermal cooling and continuous lubrication under heavy torque...
    $2,245.00
    $2,491.95
    $2,245.00

A Clearer Way to Select Your Replacement Drive

Compare the configuration details that matter before choosing a sterndrive.

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How to Choose the Right Bravo Lower Unit

A Bravo lower unit replacement should be selected from verified drive information rather than appearance alone. First determine whether your sterndrive is a Bravo One or Bravo Three application. For a Bravo One lower unit, identify whether the existing configuration corresponds to the single-water-pickup or dual-water-pickup application offered in this collection.

For a Bravo Three lower unit, confirm the drive ratio before selecting an SE128 option. The collection contains different SE128 listings for specific ratio groups, so choosing the correct ratio is an essential part of fitment. When identifiers are unclear, record the existing part number and drive information and request fitment assistance before ordering.

Check Before You Order

  • Confirm Bravo One or Bravo Three
  • Record the existing drive or lower-unit part number
  • Record available serial and model information
  • Identify the Bravo One water-pickup configuration
  • Confirm the Bravo Three drive ratio
  • Compare the information with the individual product listing
  • Do not rely on appearance alone
  • Request fitment assistance if any detail is uncertain

SE121 vs SE122 Bravo One Lower-Unit Comparison


Use this table to compare the two Bravo One lower-unit configurations currently represented in this collection. It is a shopping guide, not a universal compatibility chart. Final fitment should be confirmed from the installed drive information and the selected product page.

SE121 Bravo One Lower Unit SE122 Bravo One Lower Unit
Bravo One application Bravo One application
Single water pickup Dual water pickup
Manufacturer model: SE121 Manufacturer model: SE122
SKU / MPN: 90-121-02 SKU / MPN: 90-122-02
Select when the listed Bravo One application requires the single-water-pickup configuration Select when the listed Bravo One application requires the dual-water-pickup configuration
Main selection variable: Water-pickup configuration Main selection variable: Water-pickup configuration
Verify Bravo One drive identification and existing water-pickup configuration Verify Bravo One drive identification and existing water-pickup configuration
Do not choose from appearance alone Do not choose from appearance alone
Confirm the selected product page before ordering Confirm the selected product page before ordering

Model number alone does not confirm fitment. Before ordering a Bravo One lower unit replacement, verify the drive family, installed identifiers and the water-pickup configuration of the existing unit.

Which Bravo Sterndrive Assembly Do You Need?

A Bravo lower unit, upper unit and complete sterndrive solve different repair needs. Identify which assembly requires replacement before choosing a Bravo One or Bravo Three drive component.

Complete Sterndrive

  • Combines the major upper and lower sterndrive assemblies into one replacement drive configuration.
  • Consider a complete Bravo sterndrive when the repair involves both major drive assemblies.
  • It may also be the better shopping path when the existing upper and lower assemblies cannot be confidently retained as a matched configuration.
  • Confirm the Bravo drive family, application details and required configuration before ordering.
  • Compare a complete-drive replacement with separate upper- and lower-unit repairs before making the final purchase decision.

Upper Unit

  • The lower gearcase assembly located beneath the upper drive housing.
  • Suitable when inspection confirms the repair is isolated to the lower assembly.
  • For Bravo One options in this collection, verify the required single or dual water-pickup configuration.
  • For Bravo Three lower units, confirm the correct drive ratio before choosing an SE128 option.
  • The retained upper assembly must remain serviceable and compatible with the selected replacement.

Lower Unit

  • Combines the major upper and lower sterndrive assemblies into one replacement drive configuration.
  • Consider a complete Bravo sterndrive when the repair involves both major drive assemblies.
  • It may also be the better shopping path when the existing upper and lower assemblies cannot be confidently retained as a matched configuration.
  • Confirm the Bravo drive family, application details and required configuration before ordering.
  • Compare a complete-drive replacement with separate upper- and lower-unit repairs before making the final purchase decision.
An informational comparison graphic titled 'STANDARD VS COUNTER ROTATION' showing two outboard motors and two propellers, with text explaining the difference in propeller direction when viewed from behind. The background is a real marina scene with water and boats, but the image functions as an explanatory diagram rather than a straightforward product photo.

Standard vs Counter Rotation

Standard and counter-rotation sterndrives use opposite propeller rotation to support different boat and multi-engine configurations. Standard rotation typically turns one direction in forward gear, while a counter-rotation drive turns the opposite direction to help balance propeller forces in certain setups.

Because rotation requirements can vary by drive configuration, do not rely on port or starboard position alone when selecting a replacement lower unit. Always verify the installed drive identification, required rotation, and product fitment information before

Need More Than a Bravo Lower Unit?

A lower-unit replacement is only one possible repair path. If the problem involves another portion of the sterndrive, compare the appropriate Bravo upper-unit, complete-sterndrive or broader MerCruiser drive collection before ordering. Choosing the correct assembly can help prevent purchasing a lower unit when the required repair extends beyond the lower gearcase.

Use the related collections below to continue shopping by the assembly your repair actually requires.

  1. Bravo Upper Units

    Explore replacement upper-drive options when the required repair is isolated to the upper assembly.

    Shop Bravo Upper Units

  3. MerCruiser Sterndrive Applications

    Browse related MerCruiser sterndrive families when your existing drive is not covered by the Bravo lower-unit options on this page.

    Explore MerCruiser Sterndrives

Replacement Lower Units for MerCruiser Bravo Applications

This collection brings together aftermarket replacement lower units for selected MerCruiser Bravo One and Bravo Three sterndrive applications. Bravo One shoppers can compare SE121 single-water-pickup and SE122 dual-water-pickup lower-unit options, while Bravo Three shoppers can browse SE128 lower units organized by listed drive ratio.

Selecting the right Bravo lower unit requires accurate application information. Check your existing drive family, identifying numbers and the configuration relevant to the product you are considering. For a Bravo One lower unit replacement, water-pickup configuration is an important distinction within this collection. For a Bravo Three lower unit replacement, use the verified drive ratio to narrow the available SE128 options.

What Customers Say

Clear information for the SE121 Bravo One lower

The Bravo One lower unit information made it easier to understand the SE121 single water pickup configuration. The product details helped separate it from the dual pickup option and made the fitment requirements easier to review before selecting a replacement.
Caleb Morgan Verified buyer
August 2026

Helpful comparison of single and dual water pickup

The collection made the difference between the SE121 single water pickup and SE122 dual water pickup configurations much clearer. Checking the existing lower unit and water inlet arrangement before choosing the replacement was especially helpful.
Austin Palmer Verified buyer
June 2026

Easy to identify the correct Bravo Three ratio

The SE128 Bravo Three options were organized well enough to compare the available gear ratio groups. The 1.36 and 1.50 configuration was easy to distinguish from the other SE128 lower units. Confirming the existing ratio before ordering is an important step.
Grant Sullivan Verified buyer
March 2026

Useful details for the SE128 1.65 configuration

The information for the SE128 Bravo Three 1.65 ratio lower unit was straightforward. Having the ratio identified directly in the product information made it easier to compare against the other Bravo Three lower unit configurations.
Logan Pierce Verified buyer
November 2025

Good overview of the Bravo lower unit options

The collection provided a useful comparison between Bravo One and Bravo Three replacement lower units. The SE121, SE122, and SE128 configurations were easier to distinguish by water pickup style and gear ratio, which helped make the selection process clearer.
Cameron Ellis Verified buyer
July 2025

Helpful Guides

Use these guides to identify your MerCruiser drive, understand gear-ratio selection and decide whether you need a complete sterndrive, upper unit or lower unit.

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Close-up of a MerCruiser Bravo Three lower unit gearcase with visible identification tag and serial number plate on a workshop bench

MerCruiser Bravo Gear Ratio Guide: How to Find the Right Ratio

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Bravo lower unit gearcase, upper unit gearcase, and complete sterndrive assembly arranged side by side on a marine workshop bench

Bravo Lower Unit vs Upper Unit vs Complete Sterndrive

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Frequently Asked Questions

How do I know which Bravo lower unit I need?

Start by confirming whether your sterndrive is a Bravo One or Bravo Three and recording the identifying information from the existing drive. For Bravo One applications in this collection, check the water-pickup configuration; for Bravo Three SE128 applications, confirm the drive ratio before ordering.

What is the difference between the SE121 and SE122 Bravo One lower units?

The SE121 and SE122 listings are separated by water-pickup configuration. SE121 is listed as the Bravo One single-water-pickup option, while SE122 is listed as the dual-water-pickup option, so verify the configuration on your existing drive before selecting a replacement.

How do I choose between a single-water-pickup and dual-water-pickup Bravo One lower unit?

Match the replacement to the water-pickup configuration required by your existing Bravo One application. Do not choose an SE121 or SE122 lower unit from appearance or price alone; compare your drive information with the product listing or request fitment assistance.

Which SE128 Bravo Three lower unit do I need?

Choose the SE128 option that corresponds to the verified ratio of your existing Bravo Three drive. This collection currently separates SE128 lower units into 1.36/1.50, 1.65, 1.81/2.00/2.20 and 2.43 ratio groups.

How do I confirm my Bravo Three gear ratio before ordering?

Use the identifying information available from your existing sterndrive and applicable service or parts documentation to verify the drive ratio. If you cannot establish the ratio confidently, request fitment assistance before selecting an SE128 Bravo Three lower unit.

Can I replace only the lower unit on a Bravo sterndrive?

A lower-unit-only replacement can be considered when the repair need is limited to the lower assembly and the retained components are serviceable and compatible. The cause and extent of the failure should be determined before deciding between a Bravo lower unit, upper unit or complete sterndrive.

Is the SE128 a Bravo One or Bravo Three lower unit?

The SE128 lower units in this collection are listed for Bravo Three applications. They are divided into different ratio groups, so the correct Bravo Three drive ratio must still be confirmed before ordering.

Can I identify the correct Bravo lower unit by looking at it?

Appearance alone is not a reliable fitment method. Confirm the drive family and identifying information and then verify the application-specific selection variable, such as water-pickup configuration for the Bravo One options or ratio for the Bravo Three SE128 options.

What information should I provide for a Bravo lower-unit fitment check?

Provide whether the drive is a Bravo One or Bravo Three, the available serial or model information, the existing drive or lower-unit part number and clear photos if needed. Also provide the current water-pickup configuration for a Bravo One application or the verified ratio for a Bravo Three application.

Should I buy a Bravo lower unit or a complete sterndrive?

Choose based on which assembly actually requires replacement. If the problem is isolated to the lower assembly, a Bravo lower unit may be appropriate; if damage or wear extends into other major drive components, evaluate an upper-unit or complete-sterndrive replacement before purchasing.

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