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Old 25-10-2019, 06:11   #1
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Lost forward propulsion

Have just lost forward gear completely in my Km35p transmission on a shaft drive 3jh4e yanmar engine. Regardless of the revs in forward gear I get almost zero power but have reverse gear working as normal so was lucky to be close enough to return to the dock in reverse. Guessing the drive cone is gone? Not sure?

Would the whole gearbox need replacement? Or is this something that can be individually replaced. Only 1000 hours on engine.

Yanmar prices in Europe seem to be about 3,000 plus vat but is there refurbishment options that anyone else would know of?

Appreciate any input.
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Old 25-10-2019, 07:29   #2
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Re: Lost forward propulsion

No knowledge of the KM35p transmission. I doubt anyone could tell you definitively whether the tanny can be reparired or not without taking it to a shop and openning it up. Several years ago I had a transmission failure in the Velvet Drive on my Yanmar 4JH4AE due to a failed damper plate (Velvet Drive Failure). I had lost reverse gear. The tranny was repaired by a mechanic at less than 1/2 the cost of a replacement. So it can be done.

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Old 25-10-2019, 07:32   #3
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Re: Lost forward propulsion

I had lost reverse gear. The tranny was repaired by a mechanic at less than 1/2 the cost of a replacement. So it can be done.



John[/QUOTE]


Yeah ok Im thinking that may be a cheaper option. The gearbox has to come off regardless?

Have now drained transmission fluid and its really dark and full of brass fillings.

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Old 25-10-2019, 13:55   #4
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Re: Lost forward propulsion

Agree with jstevens, almost certainly repairable though I don't know that transmission either. Any gearbox place should be able to do it. Bit poor that it's only done 1000 hrs & crapped out. Parts prices may be a shock.
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Old 25-10-2019, 17:27   #5
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Re: Lost forward propulsion

The bronze filings are probably from the cone clutch and if just the cone is worn out it's about a $1000 rebuild but if the surface that the cone relies on for the lockup is worn then that whole single drive part must be replaced. Bearings and seals are easy to get from a local bearing supplier but the gear and cone are "Yanmar OEM" and that's where you'll spend the big bucks.
Incidentally, regardless of whether you rebuild or replace the gearbox pay very close attention to the instructions for setting up the arc of travel for the shift control lever on the side of the gearbox, the arc must be more than 38 from neutral to either ahead or astern and this is not easy to achieve if the cable and connections are worn and sloppy or the cockpit control is worn out or restricted in its travel.
While the gearbox is out, take a close look at the damper plate for signs of wear too and grease the spline when you put her all back together.
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Old 25-10-2019, 18:30   #6
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Re: Lost forward propulsion

A repair of the gear box is not out of reach for any reasonably mechanically competent amateur. There is at least one thread on CF of someone repairing their transmission although I don't remember what make it was.
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Old 25-10-2019, 23:22   #7
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Re: Lost forward propulsion

Quote:
Originally Posted by skipperpete View Post
The bronze filings are probably from the cone clutch and if just the cone is worn out it's about a $1000 rebuild but if the surface that the cone relies on for the lockup is worn then that whole single drive part must be replaced. Bearings and seals are easy to get from a local bearing supplier but the gear and cone are "Yanmar OEM" and that's where you'll spend the big bucks.
Incidentally, regardless of whether you rebuild or replace the gearbox pay very close attention to the instructions for setting up the arc of travel for the shift control lever on the side of the gearbox, the arc must be more than 38 from neutral to either ahead or astern and this is not easy to achieve if the cable and connections are worn and sloppy or the cockpit control is worn out or restricted in its travel.
While the gearbox is out, take a close look at the damper plate for signs of wear too and grease the spline when you put her all back together.


Thanks for the response.

Your right, the drive cone part alone is 500 and if some of the other drive parts are also worn such as in the diagram below the price would quickly add up.


I noticed the cable is in good condition but already extended to its full adjustment for forward gear, and when disconnected from the cable doing the gear change by hand on the lever the results were the same.


Strange thing was after draining all that oil and starting the engine quickly forward gear engaged and power applied as normal?

I got a new quote for a complete new gearbox from the UK at 1,800 so I think I might go with that considering cost of parts for a total rebuild.

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Old 26-10-2019, 01:26   #8
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Re: Lost forward propulsion

If you're going with a new gear box consider a new drive plate as well.
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Old 26-10-2019, 04:15   #9
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Re: Lost forward propulsion

I suspect looking at the oil removed-which shows signs of overheating-that there has been unnoticed slippage for some time and that either/or/both ahead clutch surface on the cone or gear are worn beyond tollerance. As has been said the gear box is most likely repairable but will require removal and dismantling for complete diasgnosis and at the 1800 euro you say you can get a new unit for I would probably recommend that path given what you say the cost of parts are. You could always rebuild the damaged one yourself over time as a spare. You must as has been said above check for proper actuator adjustment and have a good look for other reasons for such premature failure.
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Old 26-10-2019, 09:11   #10
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Re: Lost forward propulsion

Maybe some idiot put hypoid type oil (T&D) in it. I fought the Aisin stick trans in my jeep for years until I changed to 30 weight. Valvoline also makes oil specificallyfor synchromesh trannies, which is sort of what cone type gearboxes are.
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