Technodrive gearbox problem...

[Iain C]

I have a Technodrive gearbox fitted to my Lombardini engined Sabre 27. I noticed a bit of a problem this weekend, which I don't think has ever happened before.

Essentially, when it does into gear from neutral, something somewhere is "slipping", as you get a few seconds of higher revs before anything happens (although during this slipping phase, the propshaft does turn). Then whatever has been slipping "bites", the revs drop a bit and off she goes. Once you've had the "bite" there is no further slip, and once she is under way all is well, however this makes marina maneuvering a bit scary.

It's actually very difficult to see if the propshaft does suddenly turn faster after the "bite" but it must be. I'm fairly convinced this is a gearbox problem rather than either a loose prop or a fouled prop, as the "bite" is so sudden and obvious.

Any thoughts? Does the ATF fluid need changing? TBH if it's a gearbox out job it's very easy to do thanks to great access...at the beginning of the season I did have it out to swap the drive plate (broken springs) and I did the whole job in 2 hours flat, but I don't think this can be in any way related.

Thanks

 

[earlybird]

Presumably you've checked the gear-cable adjustment. A change of ATF might be worth doing.
I'm not familiar with all the Technodrive designs, but these small mechanical boxes usually have a self-servo action on the cone-clutches, ie the more torque that is transmitted, the harder the cones are driven together.Your problem of sudden take-up could be a symptom of cone wear, allowing initial slip, then full engagement.

 

[VicS]

I have a Technodrive gearbox fitted to my Lombardini engined Sabre 27. I noticed a bit of a problem this weekend, which I don't think has ever happened before.

Essentially, when it does into gear from neutral, something somewhere is "slipping", as you get a few seconds of higher revs before anything happens (although during this slipping phase, the propshaft does turn). Then whatever has been slipping "bites", the revs drop a bit and off she goes. Once you've had the "bite" there is no further slip, and once she is under way all is well, however this makes marina maneuvering a bit scary.

It's actually very difficult to see if the propshaft does suddenly turn faster after the "bite" but it must be. I'm fairly convinced this is a gearbox problem rather than either a loose prop or a fouled prop, as the "bite" is so sudden and obvious.

Any thoughts? Does the ATF fluid need changing? TBH if it's a gearbox out job it's very easy to do thanks to great access...at the beginning of the season I did have it out to swap the drive plate (broken springs) and I did the whole job in 2 hours flat, but I don't think this can be in any way related.

Thanks

Check the adjustment of the cables/ linkages to the control. Critical I believe

It might be wear in the selector mechanism in the box or wear of the cone clutches.

I did Google search a while back and discovered that this seems to be a known problem. It'll get progressively worse until it does not engage at all.

AFAIK it does not have the "self servo action" that earlybird talks about but he may be right.

 

[Iain C]

Right, now I'm completely confused on this!

I went down to the boat at the weekend, we've got a lot on at the moment (building a house) and my plan was to scrub her off and get the rig down ready for the winter and possibly next summer out. Sure enough, before I dropped the swinging mooring, there was no drive for several seconds (and no propwash astern), and then watching through the cockpit floor hatch (which gives me a great view from gearbox to stern gland) eventually something "bites", the revs drop as the load comes on, the engine moves slightly on it's mountings and we're off.

However, looking at this video...

https://youtu.be/GX_3hvMn-j0

...in this previous thread...

http://www.ybw.com/forums/showthread.php?179029-TWIN-DISC-TECHNODRIVE-TMC-40M-GEARBOX-PROBLEM

...my symptoms are absolutely nothing like it. This guy's propshaft is obviously rotating ever so slowly until it bites. However, as soon as mine goes into gear, it's running at quite a speed, even at tickover. The propshaft coupling is pretty much a blur, you can't see any individual components as it's all rotating too quickly.

So at this point I've convinced myself that the prop is obviously about to fall off the end of the shaft. Which I promptly dismiss as soon as the tide goes out and the pins, nuts, etc all seem to be present and correct. I did not remove the prop and see if the key was there, but it's all s/s, cannot have come out on it's own, and there was no sign whatsoever of any movement or play. It's a tapered shaft too, and teeny barnacles/fouling were covering the "joins" with no sign of shear.

The prop was a bit fouled, nothing silly, but a little bit of fine weed and some barnacles. And sods law, after scrubbing off and refloating, the gearbox behaved faultlessly.

So I now don't know if I have some weird intermittent gearbox fault, that just happens to have stopped the moment I scrubbed the boat off...although there were other factors in play. I suppose the boat was sat stern down on the scrubbing piles for a tide, I'd been wobbling the prop by hand, and I re-packed the stern locker which the throttle/gearbox cables run through. That said, before I did that re-packing, the shaft was still turning fast at tickover.

Or, can even some fairly minor prop fouling have such as drastic effect as to effectively render the prop (3 blade fixed) useless for a few seconds? Yet when it finally "bites" it's as dramatic as someone pulling away in a manual car, it's pretty much instant. If it was fouling/cavitation, I'd almost expect a very slow/gradual initial "bite" on the water, and possibly more slip/surging revs when going quickly from, say, slow ahead to full power (like you get in a RIB if you are bit cack-handed), but no, it's fine on a quick opening of the throttle.

What I can't fathom is clearly the prop is going at a bit of a rate as the propshaft is turning pretty quickly the second it goes into gear. Yet I know from running my little 2.5 outboard in a test/flushing tank that it's little prop moves a huge amount of water around even when at tickover...however a big bronze prop with 16hp turning gives no propwash at all until the "bite". Odd.

In a few weeks I'll be back to get craned out...be interesting to see what happens with a stone cold gearbox and a clean prop. If the problem is back, I'll take the prop off (if it needs any kind of "persuasion" or the s/s key is visible then clearly it's not the issue). Failing that, it's gearbox out.

But I don't want to strip the box if it's some wierd cavitation...likewise I don't want to relaunch and then find the issue is back and I've missed the perfect opportunity to rebuild it!

Any gearbox engineers or fluid dynamics experts care to offer an opinion? I'm baffled!

 

[Hurley3090]

Technodrive TM 40 installed new by a BetaMarine Certifying technician has failed with very few hrs use. The problem as reported so often here and elsewhere on FORUMS is "not engaging forward while reverse is fine."
The engine doesn't rev until the gearbox selector arm is home and the gearbox to cable connection check to the manual as fine: its ATF oil level is between the marks NOT OVERFILLED; so all that appears fine.
The installation is 4 yrs old all new with the fault from BETA TECHNODRIVE.
The installation Tech says "NEW GEARBOX!!!"

 

[doug748]

The only good news is that Techodrive gearboxes are quite cheap to buy.

 

[Amlov]

There is another thread running on this same problem, which appears to be related to the forward clutch cone slipping. Sadly, as you have been told, the answer is a new gearbox.

Here is the other thread

 

[Amlov]

Sorry, hadn't spotted that you had seen the other thread.

However, it does sound like the same problem.

When I first noticed a problem with my gearbox it was very intermittent and would not happen everytime I used the boat. Also when it happened it would only be the first time I put the boat into gear that day. Once it bit and started to drive the gearbox would generally be fine all day. Also, if driven in reverse for a while it would then also be fine.

But with time it got worse, both in terms off frequently and how long the period was between putting the boat in forward and getting drive.

Andy