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Technodrive TMC60 gearbox - how does it select reverse?


wetfoot

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My son's recently acquired boat has a technodrive TMC60 gearbox that we had to take off and repair as the bolts holding it to the engine plate had sheared. (bolts are 8mm but holes in engine plate were 10mm so no wonder they sheared).

 

We got it all back using bushes in the holes but I have a couple of questions about the box if anyone is able to help me.

 

1)

The boat runs OK and drives in forward and reverse but when the prop is turning there is a rhythmic knocking sound near/inside the gearbox. It's not there when in neutral so it must be coming from somewhere after the drive plate. The gear box is pretty simple so I can't imagine what could be knocking inside it. Do these boxes usually make such a sound? If not anyone any idea what it could be?

 

2)

With the engine off and the box in forward or reverse gear my son could can rotate the prop shaft. That shouldn't be possible as he should be trying to rotate the engine as well if its in gear. He said he could rotate one way but not the other. How is this possible unless the clutch is seriously slipping, which it can't be as the boat drives well.

 

3)

This one I'm embarrassed to ask as I've dismantled car gearboxes in the past and rebuilt them and they are a lot more complicated than the TMC 60 so I should be able to work this out myself.

 

Just in case we need to take the box apart I've looked at several exploded diagrams and cannot for the life of me see how it goes into reverse.

 

All there seems to be in there is an input shaft with a gear on it meshed with another gear on the output shaft via a clutch when in forward or else via another clutch which engages a different gear, also on the output shaft, when in reverse (or the other way round). The diagrams seem to show that the smaller gear is not meshed with anything though.

 

I cannot see a layshaft or layshaft gear in the diagrams so how does the box make the output shaft reverse rotation? You need to insert an intermediate gear between the input shaft and output shaft to reverse the output rotation so there should be three gears in the box somewhere.  ?

 

 

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There is an intermediate gear running on the front gear pair. The layshaft is actually the input shaft. The double cone connects either of the lower free running gears to the output shaft on which they freewheel in neutral.

 

If you have a knock in forward gear I would look at the front gear pair and the intermediate gear and its bearings. The gearbox reverses the engine rotation in forward.

Edited by Boater Sam
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Thank you Boater Sam, that's very useful information. That explains why the schematics diagram appears to show the forward gear smaller than the rearward.

Makes sense now to double up the input shaft to act as the layshaft as well. Also handy to know that forward gear = reverse of engine rotation.

 

The knock is the same in forward and reverse, although not in neutral so if the intermediate gear is always engaged, even if its secondary gear is disconnected from the output shaft then it could be the intermediate gear. Otherwise it might be to do with the output shaft as that is the only thing turning in forward or reverse but not neutral.

 

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1 hour ago, RLWP said:

It's a double cone clutch gearbox: https://allpa.nl/media/manuals/Technodrive/TM/Workshop Manual/Workshop manual TMC 60E.pdf

 

The part with the male cones on slides on a spiral, so it's locked into gear by the rotation of the output shaft

 

Richard

Thanks Richard, That's similar to the manual I was looking at (although mine was in English (:-) ).

I can now see the intermediate gear and it all makes sense (apart from the knocking!).

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3 minutes ago, wetfoot said:

Thanks Richard, That's similar to the manual I was looking at (although mine was in English (:-) ).

I can now see the intermediate gear and it all makes sense (apart from the knocking!).

Yes, I don't like that knocking. 

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The knocking could still come from the drive plate.  Although it doesn't knock when in neutral, the drive plate isn't being loaded so will be less prone to knocking.  I've been in this situation.

The TMC60 is an appalling gearbox anyway.  after two had failed I changed it for a PRM150, an easy replacement to make as it has the same fitting to the flywheel housing.

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Yes, maybe its worth taking it off again and checking the drive plate. I'm kicking myself that I don't look at it more carefully when we had the box off but its only since then that I've heard they are prone to fail.

 

What makes the TMC60 appalling? There is so little in these marine boxes that apart from poor quality steel I can't see much that can go wrong.

(I'm not doubting your comment, just interested in the reasons as this is all a new field for me)

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6 minutes ago, wetfoot said:

So what is the alternative to a cone box?

A multi-plate clutch one like PRM hydraulics. Although technically a cone box but with fibre cones, the Brog-Warner Velvet Drive is also hydraulic and stands up to hire fleet work as well as if not better that the hydraulic PRMs. To name two.

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3 hours ago, wetfoot said:

Yes, maybe its worth taking it off again and checking the drive plate. I'm kicking myself that I don't look at it more carefully when we had the box off but its only since then that I've heard they are prone to fail.

 

What makes the TMC60 appalling? There is so little in these marine boxes that apart from poor quality steel I can't see much that can go wrong.

(I'm not doubting your comment, just interested in the reasons as this is all a new field for me)

They tend to get very harsh on take-up.  My first one was replaced FOC after nine months, the second one practically had the engine jumping through the deck after 12 months, after destroying the drive plate after eight months. .  I gave up with them and replaced it with a PRM 150, which engages almost silently by comparison.

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1 hour ago, bizzard said:

I think these TMC mechanical boxes were originally derived from machine shop reverse boxes on machines like centre lathes, millers ect. Then someone thought that they might make a good, cheap marine reverse box.

Most of the small cone clutch gearboxes seem to use the same cones

 

Richard

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