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Old 11-27-2017, 11:42 AM   #1
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Twin Disc, prop turns in Neutral

Hi folks,

My new-to-me boat has twin Cat 3209TAs, with Twin Disc trannies. On my recent trip down to the Sea of Cortez, I managed to wrap a line around one of my props. While in the water, my crew noticed that the port prop was still turning slowly while in neutral. I had never noticed this before, so we shut both motors down to clear the line.

Anyway, I have Hynautic hydraulic controls for both the motors and trannies. Could this just be a linkage adjustment problem? I will take a closer look when I return to MX in December. This certainly explains why my boat moves erratically while I am anchoring, etc. Although the prop spins, I think it is slower that when it is actually engaged in gear at idle.

Any suggestions are welcome. I'm not sure of the exact model of tranny, but I will check that next time down.

Thanks and cheers, Bill
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Old 11-27-2017, 11:52 AM   #2
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In my experience warped clutch plates, sometimes due to low fluid.
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Old 11-27-2017, 12:28 PM   #3
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Most likely Clutch plates are bad. Did you shift out of gear at higher than idle rpm? Or shift from F into R a little too fast, a little too often? Most times the trans has to come out and go to the shop. While it's cheaper just to do the plates, If there are many hours now is the time to re-build. IMO
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Old 11-27-2017, 12:34 PM   #4
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"Did you shift out of gear at higher than idle rpm? Or shift from F into R a little too fast, a little too often?"

The old style mechanical shifted TD had dry clutch plates and didnt mind shifting at speed that much.

On these the shift lever position is everything , in terms of a true neutral.
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Old 11-27-2017, 01:05 PM   #5
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Might be completely normal. All hydraulic gears will put a little bit of torque on the output coupling while in neutral. Two important questions: How much effort is it putting into the shaft? If you take a 2x4 and lean against the shaft can you stop it? How easy is it to rotate shaft by hand, engine off? Some boats the shaft is super easy to turn (a good thing) and a little effort from tranny will rotate it. Also, what direction does it rotate? FWD is better than REV.

Being a 3208TA, probably a TD MG 506 or 507. Definitely not a dry clutch box.

And don't put divers under the boat to clear a line with engine running!!
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Old 11-27-2017, 01:24 PM   #6
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Are you getting full pressure?
Are you getting full indent in fwd/rev?
If both those boxes are ticked and you have fluid and the shaft is spinning in nuetral then clutch pack is suspect so the TD tech told me recently.

Luckily for me it was a fwd/rev adjustment.
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Old 11-27-2017, 02:23 PM   #7
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And don't put divers under the boat to clear a line with engine running!!
I can't believe the diver went in. That would have gotten me walked off site permanently back at work.
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Old 11-27-2017, 02:31 PM   #8
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He said "we shut both motors down to clear the line"
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Old 11-27-2017, 02:36 PM   #9
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He said "we shut both motors down to clear the line"
But only after crew was already in the water and noticed the props rotating. I wouldn't want my engines running with a diver in the water, even though my props don't rotate in neutral.
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Old 11-27-2017, 02:36 PM   #10
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"While in the water, my crew noticed that the port prop was still turning slowly while in neutral."

I guess I got hung up on this sentence. My apologies.
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Old 11-27-2017, 03:27 PM   #11
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I have observed the prop turning with the engine shut off while drifting. A current passing below the boat will spin the propeller. This condition is generally more observables while at anchor than drifting. This may indicate a loose Cutlass bearing.
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Old 11-27-2017, 04:33 PM   #12
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But only after crew was already in the water and noticed the props rotating. I wouldn't want my engines running with a diver in the water, even though my props don't rotate in neutral.


About 10 years ago a diver got wrapped around the shaft of a commercial dive boat out of WPB. A very bad outcome. In spite of that, divers and water skiers get plucked out of the water routinely with engines on. I killed my motors on pickups to reduce CO back there.
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Old 11-27-2017, 06:21 PM   #13
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Hi everybody,

Thanks for the great replies. Yes, I initially had the motors running when the diver entered the water. My bad, I won't do it again. The tranny should have the same hours as the motor, which is shy of 1500 hours. I really didn't look too closely regarding pressure and shift lever positions, as I was in the middle of other projects. I did try to stop the shaft with my hand and did not have any luck. Don't worry, I was very careful not to grab tightly, or to get caught in the machinery. I will check all the suggested stuff in a couple of weeks.

Thanks again for the prompt and thoughtful replies.

Cheers, Bill
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Old 11-27-2017, 08:09 PM   #14
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In my experience, what that shows is that your shafts are very well aligned. I have seen that before, in one case with the main idling in neutral, the shaft would turn VERY slowly just from the fluids moving around.

IMHO, whoever aligned your shafts did an awesome job. Of course you may have screwed it up by wrapping the prop. ;-)
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Old 11-30-2017, 08:32 AM   #15
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Perfectly normal if you put on a pair of gloves and with slight pressure applied to the turning shaft (inboard of course) your hands can stop it from turning.
I do it without gloves but then I'm old school.....
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Old 11-30-2017, 09:42 AM   #16
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New to you, the type and quantity of oil certainly right?


And my Twindisc mg5061work service manual
Troubel shooting
6. No neutral.
6.1.Control valve linkage incorrectly positioned-Chek and adjust control linkage. 6.2.clutch plates warped-Replace clutch plates, Overhaul unit.


NBs
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Old 12-01-2017, 10:19 PM   #17
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Or , as long as it drags only in forward,. then learn to live with it. Yes, it will be a nuisance from time to time.
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Old 12-02-2017, 08:44 AM   #18
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Or , as long as it drags only in forward,. then learn to live with it. Yes, it will be a nuisance from time to time.
hmmm. If the boat actually moves forward in N, and the spool valve is adjusted correctly, you have clutch plates rubbing steel against fiber in N. When my boat continued to move in N, it was a pain at dockside.

I was going to say that continued slipping in N may be progressive, but I'm not positive about the TD set-up. I think some sport fish install trolling valves, that I think cause an intentional slip in the troll position to lower the vessel minimum speed. So, maybe the defect won't be progressive. But, any vessel progress in N is bad form.
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Old 12-02-2017, 10:27 AM   #19
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Might be completely normal. All hydraulic gears will put a little bit of torque on the output coupling while in neutral. Two important questions: How much effort is it putting into the shaft? If you take a 2x4 and lean against the shaft can you stop it? How easy is it to rotate shaft by hand, engine off? Some boats the shaft is super easy to turn (a good thing) and a little effort from tranny will rotate it. Also, what direction does it rotate? FWD is better than REV.

Being a 3208TA, probably a TD MG 506 or 507. Definitely not a dry clutch box.

And don't put divers under the boat to clear a line with engine running!!
I agree With Ski! Especially what I highlighted...
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Old 12-03-2017, 11:35 PM   #20
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My gear box, a TD 506, has done that for the last 32 years. It was doing it when we bought the boat so actually longer,; just don't know how much longer.

I was told when I asked about it to learn to live with it unless it got worse. It hasn't but at times it can be a nuisance especially when I'm single handing the boat.

Once it warms up the shaft slows. It's not fast but determined. I can stop it but only now check it periodically to see if it is worse.

But unless your is worse than mine just monitor it.
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