ZF Gearbox "Clunk" Noise

I have a Symbol Raised Pilot House 45 foot boat with a single installation John Deere 375hp 8.1 litre engine, ZF305A Gearbox, Vulkardan engine coupling, and a 31" x 23.5" 3 blade prop. The vessel weighs about 20 tonnes or 45,000 lbs.
I bought the vessel new from the Symbol factory in Taiwan 3 years ago and from the very fist time forward or reverse gear was engaged, it has made a very substantial "clunk" noise. It happens at all revs from idle (600rpm) and at higher rpm, but only happens at the instant that the gear is engaged. Underway, all is quiet. When the gear was engaged, the rear of the engine & gearbox "jumped" to one side (depending on whether forward or reverse gear was engaged), but this only happened at the instant the gear was engaged. Underway, it was quite stable.
I have taken the matter up with Symbol who state that they bought a "propulsion package" from the engine supplier (EMTL in Taiwan) and that it is a matter that EMTL should address.
I have taken the matter up with EMTL who claim that the engine coupling, gearbox, propshaft coupling, propshaft, and propellor were all specified by ZF and that it is a matter for ZF. In fact, I believe everything from the engine flywheel to the propnut was supplied by ZF (through their various companies) to the engine supplier.
I have taken the matter up with ZF who claim there is nothing wrong with the gearbox or their equipment. This may be true as it has held together for 3 years so far!
I made enquiries with John Deere regarding the alignment of all parts. They were quite helpful and made some suggestions including the lowering of the rear engine mounts which has been done. The lowering of the rear mounts has stopped the rear of the engine and gearbox "jumping" to one or the other side.
However, the substantial "clunk" noise is still present. ZF again looked at the installation and have stated that there is nothing wrong with the gearbox.
Everything along the driveline has been checked for tightness and alignment, and is all fine. I feel sure that the "clunk" noise emanates from the gearbox possibly due to the gearbox engaging too quickly.

Surely, this "clunk" noise is NOT normal.
Has anybody else had a similar experience? and can they make some suggestions?

I would in particular like to hear from anybody with the same or similar boat/propulsion package. Even better would be a response from somebody with the same boat, Symbol RPH45 with a single engine installation, AND a ZF305A gearbox.

Hoping to hear from somebody.
Owen

Hi Garry,

Thanks for your input.

You apparently have gearbox knowledge and understand that this a constant mesh beveloid gearbox in which the actual gears are constanly engaged, and engaging forward or reverse simply actuates the one of the two hydraulic clutches.

Yes, I have tried your suggestion.
I have disconnected the gearbox cable control at the gearbox control valve, and then engaged gear by manually moving the control valve lever. And I get the "clunk" noise.

The only way of NOT getting the "clunk" noise is to move this lever EXTREMELY slowly (far slower than would happen in normal use) in which case the gearbox engages smoothly without noise.

ZF changed the control valve earlier but that made no difference. There is aparently no adjustment of flow rate on the ZF305A box, and ZF do not want to change the "engagement speed" by altering the flow rate. They claim doing so may affect the longevity of the clutches.

I guess that is why I would like to hear from other owners with the same gearbox to find out if they have the same problem, and if so, how it was fixed.

I look forward to your comments Garry.

Owen

Hi Guys,

Firstly, thanks for your responses and for your input.

The engine mounts have been changed from Barry Mounts to Cushyfloat as specified in the John Deere parts manual. In fact, I think they are the same mounts that John Deere use on the next up engine size.
No change to the noise though!

The engine rpm at idle is 600rpm. Further, this engine has full electronic control. It has been suggested that the "engine mapping" could be changed. This was suggested to John Deere but they felt that nothing would be achieved by doing this. It would not be easy to lower the rpm without altering the engine software as I understand it.

Yes, I agree with the comments about the trolling valve. I doubt that that will help either.
The "Clunk" sound does sound as if it has something to do with the "lag" of the Vulkardan coupling which overshoots once the prop overcomes the reluctance and starts turning (if that makes sense).
Originally we suspected that the Vulkardan coupling was hitting the safety stops (get home stops in case the coupling material fails) but the Vulkardan coupling has also been changed and the Vulkardan distributor checked the original and claimed that it was not hitting the stops.
According to my ears (and they have done some mileage and don't work like they used to) the noise is coming from within the gearbox. I know noise travels but cannot think of anywhere else it could be coming from, especially as everything has been checked and found to be tight, and the propshaft alignment has been checked and found to be "perfect" according to the guy who checked it.

Maybe, that is "just the way it is", but I would really feel a lot more comfortable about it if there were others with the same "clunk" noise.

I look forward to any further comments that anybody can provide.

Owen

Zf Gearbox Noise

Thanks Guys,

Yes, K1W1, I have tried engaging gear at 5 knots and still get the "clunk" noise.

And, yes NYCAP123, I have listened with a stethoscope and reckon the noise is coming from the gearbox, but the gearbox is bolted solid to the coupling housing which is also bolted solid to the engine, and I know noise can travel.

Any more clues, guys?

Thanks for your suggestions to date.

Owen

Zf Gearbox Noise

Thanks Capt J,

No, there is not any side to side movement of anything.

Bear in mind that the Vulkardan coupling housing is bolted directly to the engine flywheel housing, and the gearbox is bolted directly to the coupling housing.

Futher, the propshaft coupling bolts directly on to the output flange on the rear of the gearbox.

Effectively, everything from the prop to the engine flywheel is one rigid arrangement with the Vulkardan coupling absorbing the torque changes and the clutches in the gearbox engaging as required (one for forward and the other when reverse is engaged).

I hope that clarifies the installation somewhat.

Thanks for the input. Any more suggestions?

Owen

Hi Capt J,

Thanks for the further response.

My thoughts also at first, but no. Everything is tight.

And the propshaft can be turned by hand. Certainly, it takes some effort but can be done. It would be fair to say that it is firm to turn.

Thanks, Have you any other suggestions?

Owen

Zf Gearbox Clunk Noise

Thanks Capt J,

That's a good suggestion. I have changed the oil & filter about 200 hours ago without any change to the noise. However, the viscosity of the new oil looked more like 15-20W. So a slightly heavier oil may slow down the engagement speed as well as deaden the noise somewhat.

I will try that within the next couple weeks.

A great suggestion. Thanks.

Owen

It is some years since I started this thread, so I thought an update might be in order.
I still have the boat, & I still have the noise, just as I had originally.
I have done 1200+ hours and in all that time, the "clunk" when the prop is engaged is still just the same.
The good news is that it has never caused me any issues.
I have also spoken to owners of other makes with similar "clunks" and without problems.
So, it looks like the "clunk" is here to stay, and probably just because the coupling is fairly rigid. Sometimes I think the coupling should be a lighter version with more "give" when the prop is engaged, but a lighter version may fail.
No issues for 11+ years is a good result, and I imagine it will be with the boat forever. In fact, it is almost nice to hear the prop engage.
Thanks to all who posted on this issue. I hope my update after 11 years is helpful.