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Old 27-07-2008, 14:27   #1
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Transmission slipping? 3GM30F

I have a 3GM30F with the standard reduction gear KM 2. Lately, I have noticed that while motoring in a dead calm at about 6 knots my boat will slow down to 3 to 4 knots but the rpm remains the same or about 2500 rpm. I read the manual and it is a cone drive so I doubt it would slip. Any suggestions?
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Old 27-07-2008, 15:39   #2
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How are you measuring your speed.

Paddlewheel or GPS
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Old 28-07-2008, 13:55   #3
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How are you measuring your speed.

Paddlewheel or GPS
I used the GPS for speed.
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Old 28-07-2008, 17:14   #4
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Check your transmission fluid.

Is it ATF or Engine Oil?
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Old 28-07-2008, 17:18   #5
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There is another thread on this. If you find you have ATF in the trans, it will most likely need to be rebuilt.

The KM-2 uses engine oil. It should be stamped into the trans case.
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Old 28-07-2008, 17:20   #6
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cone clutches can slip. most notably they slip on engagement and present as a vibration at low speed the clears at higher speed.
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Old 28-07-2008, 19:55   #7
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If the tide is moving out or in at two knots and you are usually going six knots, than you are going to lose two knots if you are going against the tide. You could have a crab trap line or something fowling your prop take a dive down there and check it out.
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Old 29-07-2008, 01:43   #8
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I would be considering tides. So what happened with your paddle wheel speed? The other way to verify is to borrow an IR beam rev counter. Place a reflective patch on the shaft and verify the shaft RPM when the boat starts slowing. If it is shaft slowing, follow the above info from Pat and Chief.
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Old 29-07-2008, 06:38   #9
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Check your transmission fluid.

Is it ATF or Engine Oil?
First, thanks to all who responded. It is this kind of action that makes me want to return to the forum daily...I never know what I might learn. Regarding the oil. I use engine oil. However, I had recently changed the oil and discovered that I had slightly over filled.

Regarding motoring against the tides. We have strong tidal currents here in Panama and I always check the tides before I go out so I know what to expect. I am certain that it is not tides or crab traps (no crabs here). I really like the idea of the RPM counter but not a item I want to buy or readily available to borrow. At least it sounds like it is not something serious and I won't get stuck in one of the outer islands and unable to return home.
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