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Mercury 7.5 lower unit frozen/rusted on?

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  • Mercury 7.5 lower unit frozen/rusted on?

    1976 Mercury 7.5 longshaft motor. I can't remove the lower unit to rebuild the water pump. I got the 2 nuts removed but the lower unit won't slide of. The housing is loose but it feels like something is still holding it in. The Merc dealer seems to think the drive shaft is rusted to the power head and suggested I pry it off. Is he right or is there a hidden bolt or screw I've missed?Thanks...

  • #2
    Re: Mercury 7.5 lower unit frozen/rusted on?

    Hi odieThere should be three nuts. Two on the sides and one under the cavition plate toward the rear.

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    • #3
      Re: Mercury 7.5 lower unit frozen/rusted on?

      No, there are onlt 2 nuts on the outside. One under the cavitation plate by the water inlet. The other on top of the lower unit on the front of the shaft. No nuts on the sides. Maybe on the bigger motors but not on this small pup. I'm 99% sure it's something hidden that is holding it toether.

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      • #4
        Re: Mercury 7.5 lower unit frozen/rusted on?

        Hi odieGuess what, your right. There is only the two nuts. See what happens when you make a call from memory. Ok, a lot of times I find that the water inlet hangs up on that stud on the under side. It sort of bites on the threads. If that isn't it, then try a little senceable prying. Where dose it feel like it's stuck, front or rear.

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        • #5
          Re: Mercury 7.5 lower unit frozen/rusted on?

          Its stuck at the front somewhere. The two studs are freeso it's not that. Its stuck somewhere inside near the front. Feels like the shaft it frozen or something.

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          • #6
            Re: Mercury 7.5 lower unit frozen/rusted on?

            My 7.5HP did that to me. Turned-out to be the shift spline froze to the spline socket..Some fast shifting with the engine running,and the bolts loose, but threaded on,in a barrel, did the trick...Forward/reverse/forward/reverse a few times. One caution. Don't shift faster than the gears can mesh, or you run the risk of breaking the shift cog. But fast enough to mess with it's little mind. Don't take no for an answer. Let us know how you do.
            "Did you hear about the guy whose whole left side was cut off? He's all
            right now."

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            • #7
              Re: Mercury 7.5 lower unit frozen/rusted on?

              where is the shift spline and socket? Is it down in the lower unit or up top by the powerhead?

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              • #8
                Re: Mercury 7.5 lower unit frozen/rusted on?

                It is a shaft off the lower unit, that plugs into a splined socket. It's on the L/U, and has the same type of spline teeth as a drive shaft, but much smaller.
                "Did you hear about the guy whose whole left side was cut off? He's all
                right now."

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                • #9
                  Re: Mercury 7.5 lower unit frozen/rusted on?

                  is this splined joint below the water line? Is it something that a water leak might cause to rust? When you removed the lower unit, does the shift shaft stay with the upper unit?

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                  • #10
                    Re: Mercury 7.5 lower unit frozen/rusted on?

                    Not under normal conditions.As it is made of stainless steel, it really doesn't rust. But it does tend to 'cement' itself to the upper shift shaft.Add to this, when you pull down ,it just tends to bind sideways.Yes, it should seperate there at that splined shaft and socket. It is somewhat fragile,due to it's small size.I take it, it didn't let go by fast shifting?
                    "Did you hear about the guy whose whole left side was cut off? He's all
                    right now."

                    Comment


                    • #11
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                      Re: Mercury 7.5 lower unit frozen/rusted on?

                      Hii Odie, Time to get physical with it. Start with brute force - a block of wood placed flat on the cavitation plate, with the corner of the block snug against the lower unit housing - you don't want to break the cav plate. Using a mallet, tap it downwards a few times, then switch to the other side. I suspect your driveshaft is rusted into the crankshaft - not uncommon on the older Mercs. If it's completely welded in there, you may be SOL, but sometimes it'll come out with some gentle persuasion. If that doesn't work, you may have to pull the powerhead off - loosen all 6 bolts and lay the motor on it's tiller handle side (shift handles are breakable) on a thick blanket folded over a couple times. Pick the powerhead end up about a foot and drop it on the blanket. The sideways shock of hitting the ground sometimes loosens it up so you're not simply pulling straight out. It won't completely fall off because of the studs in the base of the powerhead. - Scott
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