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

In my experience warped clutch plates, sometimes due to low fluid.

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

"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.

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!!

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.

Ski in NC said:

And don't put divers under the boat to clear a line with engine running!!

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I can't believe the diver went in. That would have gotten me walked off site permanently back at work.

He said "we shut both motors down to clear the line"

twistedtree said:

He said "we shut both motors down to clear the line"

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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.

"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.

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.

MYTraveler said:

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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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.

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

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. ;-)

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.....

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

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.

C lectric said:

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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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.

Ski in NC said:

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!!

Click to expand...

I agree With Ski! Especially what I highlighted...

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.

Ski in NC said:

If you take a 2x4 and lean against the shaft can you stop it?

Click to expand...

I strongly agree with this advice. Grabbing ahold of a spinning shaft with gloves on is a good way to lose fingers or worse. Please be careful and best wishes.

C lectric said:

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.

Click to expand...

My TD 506's have never done that. Something is wrong, even though it might not be badly wrong I would not tolerate it.

Yes not very good advice when I relook at it. However I will stand by it as it was my best choice at the time but what I should have included was:

--get a mechanics opinion, not ours. Someone who has real experience rebuilding these things. That's what I did those many years ago. Ski in NC would fit that description as would a few others.

--It could be oil drag which was part of what I was told which is the phenomenon that your torque converter in the auto trans in you car partly works by in which case a re & re may not fix it. Often as it warms up the drag will become much weaker.

--it could be a warped disc which can be fixed but often requiring a complete teardown out of the boat.

--but first make sure it is not a maladjusted control link. It is possible the cable or the pivot pin has worn, the clamp holding the cable ferrule is loose or something else causing an incomplete movement into the neutral position. It could even be some wear in the control valve or a seal allowing too much leakage to the fwd. clutch pack. Find out.

--get an estimate for pulling and reinstalling the gear and the rebuild.

--then make a decision.

When I did my repower the gears were out of the boat and I thought there would be no need to touch them. They only had 1900 hrs, and TD is almost forever, right? Well, the screens had some debris in them. With everything else in the boat new or recon I then decided to have the gears rebuilt.

Cost was $7200 for the pair including pick up and delivery back to the yard in Port Townsend. Five years ago. Done by a guy in the Seattle area who worked from home but had a good rep. Despite the low hours the internals were not in good shape. We suspect the PO, or more likely his dumb-ass sons, had the habit of quickly changing from forward to reverse at raised rpm.

Although TD say it isn't necessary I always change gear at idle, and try to have a pause in neutral on the way through.