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OMC Cobra trim won't stay trimmed

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  • OMC Cobra trim won't stay trimmed

    Sorry if this problem has been addressed on the list but I'm new and here's my problem: My 1986 OMC Cobra (4.3L) drive unit will not stay trimmed up while under power. If you trim it up after the boat gets on plane it'll stay for a little while and then slowly drop back down. When going very slow in the shallow water eveything seems fine. The reservoir seems full and there's no sign of any fluid leaking. What could be the problem? Thanks.


  • #2
    Re: OMC Cobra trim won't stay trimmed

    Sounds like your internal seals are leaking. With the load under power, the oil is bleeding past the seals back into your reservour. Sometimes it gets better as the season goes on.

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    • #3
      Re: OMC Cobra trim won't stay trimmed

      Internal seals. Excuse my ignorance but just where are THEY located? Yeah, yeah I know - internally, but where exactly? And can I get at them without taking the boat out of the water?Joe

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      • #4
        Re: OMC Cobra trim won't stay trimmed

        the seals are inside your cylinders....they are not too bad I don't think

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        • #5
          Re: OMC Cobra trim won't stay trimmed

          I've got a similar problem. I started a new thread.
          Last edited by geoooo; June 12th, 2010, 08:57 PM. Reason: I hijacked this - sorry.

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          • #6
            Re: OMC Cobra trim won't stay trimmed

            Originally posted by geoooo View Post
            Hi,

            I'm brand new, so pardon me if I'm cutting in. I can't seem to find a "Post New Thread" button.

            Anyway, I have a similar problem with my 1989 OMC 4.3 that I just bought. After I lift the boat, the unit slowly drops to vertical within a couple hours. It seems to work fine under normal operation, but just slowly drops, like a slow leak.

            I had a mechanic tell me I need a new trim pump (solely from my description), but it goes up-down just fine with no problem.

            TIA,

            -geoooo
            PM sent to you....
            2011 Triton 190 Escape SE 150 Mercury Pro XS

            I never learned much from winning, but always learn from failure.
            Semper Fi

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            • #7
              Re: OMC Cobra trim won't stay trimmed

              Originally posted by Joe Merone View Post
              Internal seals. Excuse my ignorance but just where are THEY located? Yeah, yeah I know - internally, but where exactly? And can I get at them without taking the boat out of the water?Joe
              Its easier to replace the tilt cylinders with rebuilt ones. And No, you really cant do them in the water as they are under water most of the time.
              Replace them and then bleed the system and you should have it licked.
              2011 Triton 190 Escape SE 150 Mercury Pro XS

              I never learned much from winning, but always learn from failure.
              Semper Fi

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