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F300 Lower Unit Drive Shaft Leak?

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  • F300 Lower Unit Drive Shaft Leak?

    I posted a topic on my Lower unit earlier and have an update + follow up question

    Model F300XCB built in December 2021. I have 25" drive shafts.

    I performed gear oil changes with YamaLube Gear oil at 20, 117, 187 and 275 hours.

    When draining the gear oil at 275, I noticed my gear oil did not come out clear.

    Then after just 5 hours of use, at 280 hours, I drained it again and observed the same thing - gear oil not clear.

    I pressure tested the lower and it held 12 PSI for 12 minutes.

    I always add about 1/4 to 1/2 turn on the drain and vent screws after hand tight + new gaskets every time.

    So, now I'm thinking I have a DRIVE Shaft leak that only happens when under load.
    I do not think water is entering from the shift shaft as the pressure test came out good.

    I am of course still under warranty. What are your thoughts?

    Are drive shaft seals prone to leakage? Might I have a warbling drive shaft?

    Grady-White 330 Express

  • #2
    Well you certainly have a leak. Did you remove the lower unit when you tested it? If you do it again spray some soapy water around the seals and watch it very carefully for a good long time. Also you can spin the Lower unit over by hand and side load the shafts while you are looking for leaks.

    You say it under warranty so I am not sure what your particular dealer say about you fooling around with it yourself so be mindful of that.

    If you feel you may have a bent prop shaft or driveshaft you can buy a dial indicator and holder online these days for cheap and measure the run out quite easily. You would need to know the limits from your service manual if you have one.

    I know that if your prop shaft was bent...even slightly it would cause vibration that you should notice easily. I just touched a rock a few years back..only nicked one blade and my F70 shook so bad I could only idle all the way home. When I checked the shaft after removing, it was bent only 0.035"

    Good Luck


    • #3
      Final Analysis of my leaking Lower Unit by my Yamaha Service Tech. = Bent prop shaft.

      I recall hitting something while cruising at 4,400 RPM's this Summer.
      After the thump I immediately looked back at my wake expecting to see something (which I didn't).

      I probably hit an Ocean Sunfish or possibly a whale. I am surprised my F300 didn't kick up upon impact.
      Slightly bent my skeg as well yet my SS Prop is 100% fine. My lower is in for repairs now...

      Just wanted to share this to close out my question posted earlier.
      Grady-White 330 Express


      • #4
        Thanks for reporting your solution...helps others.