Yamaha Aftermarket Lower Unit – Replaces 75–100HP 2/4 Stroke – 2.0 & 2.3 Gear Ratios – 18 Spline – 20″ & 25″ Shafts – SEI 90-404

Original price was: $1,326.45.Current price is: $1,195.00.

(26 customer reviews)
Use the coupon code WELCOME5 at checkout to get 5% off on your first order

“SE404 (ST-90-404) Yamaha outboard lower unit for 2-stroke & 4-stroke 75-100 HP engines. Durable paint, high-quality materials, and superior performance. Compatible with standard rotation, not for counter-rotation engines. Order now!”

Description

Replaces some Yamaha 2-stroke and 4-stroke 75-100 HP Standard Rotation Lower Units.
Does not fit 2016-present 4 stroke engine models ending in “B”
The paint color is Black. You can paint it to match.

Additional information
Weight 65 lbs
Dimensions 37 × 10 × 61 in
Ratio/Shaft/Motor

2.0 Ratio/20" 18 spline/2-Stroke

,

2.3 Ratio/20" 18 Spline/4-Stroke

,

2.3 Ratio/25" 18 Spline/4-Stroke

Brand

Brand

Yamaha

Reviews (26)
3.9
26 reviews
8
7
11
0
0

26 reviews for Yamaha Aftermarket Lower Unit – Replaces 75–100HP 2/4 Stroke – 2.0 & 2.3 Gear Ratios – 18 Spline – 20″ & 25″ Shafts – SEI 90-404

Clear filters
  1. Pamela Gibson

    No special tools needed. Done in a coffee break!

  2. Taylor Hendrix

    The unit’s grease ports are strategically placed for easy maintenance. Installed it in 40 minutes, and performance has been flawless. OEM should take notes!

  3. John Simmons

    No more overheating issues. Runs like new!

  4. Alexander Wood MD

    Why I waited so long? This unit revived my boat. Smooth, reliable, affordable. Don’t hesitate—buy it now!

  5. Edward Smith

    Rugged housing handles storms. Budget-friendly beast!

  6. Darren Wells

    The packaging included foam inserts to prevent shipping damage. Installation was tool-free, and the unit meshes perfectly with my motor. No leaks or noise—highly recommend!

  7. April Watson

    The included torque specs ensured a proper installation. Two months later, the unit performs like new—no noise, no leaks, no regrets. A perfect aftermarket solution!

  8. Emily Lopez

    The packaging included foam inserts to prevent rattling during transit. Installation took 30 minutes, and the unit meshes perfectly with my motor. No vibrations or leaks—extremely impressed!

  9. Emily Parks

    The unit’s grease fittings made maintenance a breeze. Installation took 40 minutes, and performance has been flawless through 15 hours of runtime. OEM should take notes!

  10. Megan Gonzales

    I’ve used this in both freshwater and salt—zero issues. The stainless steel components stay pristine, and the shifts are crisp. A reliable, affordable solution!

  11. Robin Washington

    Mounted yesterday—handled a full day on the water flawlessly.

  12. Amber Le

    Survived saltwater testing—zero corrosion. Solid engineering!

  13. Mr. Nathan Hernandez

    Perfect for DIYers. Saved $$$ on mechanic fees.

  14. Veronica Cox

    The customer team replied to my midnight query in minutes! The unit is quiet, durable, and leak-proof. A standout in aftermarket parts—highly recommend!

  15. Anne Thornton

    Tested this in icy lakes and tropical waters—no issues. The stainless steel gears handle temperature swings effortlessly, and the shifts stay precise. A four-season workhorse!

  16. Aaron Jackson Jr.

    Everything arrived securely packaged with all hardware included. Installation was a breeze—no missing parts or confusing steps. After two months of heavy use, it still runs like new. Worth every penny!

  17. Johnny Greene

    This unit survived a month-long expedition in Alaskan waters. No corrosion, no leaks, and shifts are as smooth as day one. OEM engineers should take notes!

  18. Danielle May

    Reduced vibration by 90%. Feels factory-new!

  19. James Watts

    The unit’s powder-coated finish resists chips and scratches. Installation took 35 minutes, and performance is flawless. Why spend more on overpriced OEM parts?

  20. Jamie Vaughn

    Pre-greased fittings saved me 30 minutes of messy work. Installed solo, and it’s been flawless through 50 hours of runtime. DIYers, this is your holy grail!

  21. Kimberly Patterson

    Direct replacement—no modifications needed. Works perfectly!

  22. Carrie Jones

    Great support—quiet and durable. Standout product!

  23. Andrea Stephens

    I’ve tested this unit in saltwater for three weeks, and there’s no sign of corrosion. The gears engage smoothly, and it’s noticeably quieter than my old OEM part. Highly recommend for marine use!

  24. Kimberly Morris

    Not a single leak. Performs like it’s brand new.

  25. Eric Calhoun

    This unit saved my boating season. Installed in under an hour, it’s outperformed my old OEM part with smoother shifts and better fuel efficiency. Worth every cent!

  26. Shannon Jacobs

    Installed this on a 2005 motor—fit like a glove. Smooth engagement, no vibrations, and saved $700. Vintage boaters, this is your fix!

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