Mercruiser 120hp 140hp Upper Pre/R/MR/Alpha One 1.98 Gearset 43-55778A3 Gearcase

Mercruiser 120hp 140hp Upper Pre/R/MR/Alpha One 1.98 Gearset 43-55778A3 Gearcase

SAME DAY SHIPPING ON THIS ITEM if you order & pay before 12 PM EST (Noon) MON-FRI.*(see disclaimer below)
*This will/might not be the case for 
1. USPS Holidays, as most of my items are shipped via USPS
2. Inclement weather in my region.

Item Details

  • All 120hp 2.5L & 140hp 3.0L 4cyl applications for Pre-Alpha/R/MR/ALPHA ONE Gen 1, so 1970-1990 as a general rule.
      • (Actually these were also used on Gen II drives 1991-1997)
  • The gear set here is MerCruiser 43-55766 / 43-55778 > 43-55778A3 (Also Equivalent to 43-55766A2 / 43-55766A3 / Sierra 18-2205)
    • 20-24 (tooth count) 1.98 Ratio for 4-cylinder GM Chevy 120hp 2.5L 153CID / 140hp 3.0L 4cyl 181CID sterndrive engines.
    • Also Included is upper driveshaft assembly 45-55797
  • If you have any questions on compatibility, or any other questions about this item, please don't hesitate to contact me.
  • The existing bearings are probably fine, but please inspect bearings beforehand to make sure they are to your liking as your races may be different than the bearings here, its always recommended to start with fresh bearings & races when performing this type of service work, but this is ultimately up to your discretion.
  • Freshwater Used Parts.
  • These look great and  were removed from a completely functional upper gearcase.
  • Purchase with confidence!

1970 1971 1972 1973 1974 1975 1976 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990

Compatibility Statement / Disclaimer

  • Please check with me or your parts manual if you are unsure if this is correct for you. The part numbers given here are all correct, but it is ultimately up to you to do a little bit of research and make sure this is what you need.
  • The compatibility statements or suggestions in this listing is my best guess based on the quick research I did for this item.

Return Policy (The Fine Print):

I try to describe all of my items honestly and accurately to the best of my ability. If you are dissatisfied with your recent purchase, please contact me as soon as possible. Returns must be made within 14 days, buyer pays shipping. I stand behind the products I sell and if something doesn't seem right with your purchase or you are having unexpected difficulties, please contact me as soon as possible and give me the opportunity to correct the issue. In the event that an item has unexpected functional issues within the return period, I will either: A. Let you keep the item and offer a full refund B. Ask that you ship the item back to me and offer a full refund and cover the return shipping as well.


These are used parts. Used parts may have cosmetic issues (scratches, missing paint, faded plastic, pitting, rust, minor dents & dings, etc.) The condition of this item is as described in the description and visible in the picture. You will receive the items you see in the picture (unless noted otherwise) It is being sold "as is" with no warranty.