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Old 03-13-2017, 10:46 PM   #1
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Gearbox rattling

I re-powered about 2 years ago with a 42 hp Vetus diesel (Mitsubishi based) and a ZF-25A gearbox.

The gearbox is a ~7 degree downangle design and a 1.98:1 ratio. The ZF-25A is one size up from what Vetus was originally offering with this engine.

The gearbox was always a little bit rattly when in gear at low rpm (850-1000rpm), although just recently it seems to gotten slightly worse (rattling from 850- 1200 rpm). The rattle is louder than the actual engine noise. Over 1200n rpm it is nice and quiet.

I've heard a variety of opinions from "this is normal" to "change from ATF to a 10/40 engine oil". A search on the web suggests this is a common problem with many gearboxes, but opinions vary considerably as to what to do about it, or if this is anything more than a nuisance noise.

Any suggestions from the TF forum?
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Old 03-13-2017, 10:55 PM   #2
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Could be the damper plate failing. It attaches to the engine flywheel and drives the gear input shaft often using springs for pulse and shock absorption. Eventually the springs fail and break. That can cause the noise and if left will fail completely leaving you without drive.
One possibility.
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Old 03-14-2017, 05:15 AM   #3
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Could be the damper plate failing. It attaches to the engine flywheel and drives the gear input shaft often using springs for pulse and shock absorption. Eventually the springs fail and break. That can cause the noise and if left will fail completely leaving you without drive.
One possibility.
Could be, but I've never heard of one failing when new. (the noise was there right from the start) Less than 300 hours on the engine & gearbox now.
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Old 03-14-2017, 06:06 AM   #4
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At low rpm the gears just aren't loaded up and the sound is gear slap when the gears are torqued up they load up and the tolerance between the gears reduces so dose the noise .
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Old 03-14-2017, 06:22 AM   #5
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Had a relatively new one loose a punch out and thee punch out balled up and created all kinds of funny noises at different RPMs.

Not likely if your sound is constantly similar at the same rpm as you vary them...but a weird one for me.

Maybe yours isn't failing bit loosened up somehow?
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Old 03-14-2017, 08:25 AM   #6
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Spring type torsional couplings are wear items. As they age, their performance degrades. A ZF 25 I think is a mechanical gear and it will be a noisy beast behind a four banger at low rpm.

Those gears are usually spec'd for sailboats where the noise is not an issue for various reasons.

There is gear rattle from the natural torsional reversals from the engine, but also fwd torque is what keeps the clutches in the gear engaged. The torsional reversals alternately engages and disengages the clutch, and that wears the mechanism out.

Try to avoid running where it rattles. Eventually you will get poor engagement in fwd.

Where noise would be an issue, hydraulic gears are spec'd with rubberized torsional couplings.

That's why they developed the "Velvet Drive" and trademarked it. Soft shifts and a quiet drive.
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Old 03-14-2017, 08:35 AM   #7
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I think Ski nailed it. A mechanical gearbox like yours can be noisy under certain circumstances.

There is even a disclaimer in the latest ZF 25 A factory brochure:

Torsional Vibration and Torsional Couplings

The responsibility for ensuring torsional vibration compatibility rests with the overall propulsion system integration responsible party. Compatibility check of torsional vibration must include excitations induced by engine governor. ZF cannot accept any liability for gearbox noise or for damage to the gearbox, the flexible coupling or to other parts of the drive unit caused by torsional vibrations. Contact ZF for further information and assistance.


And from the ZF Repair Manual: ZF25A, ZF25, ZF45A, ZF45-1:

Troubleshooting

14. Chattering transmission noise mainly at low engine speed

14.1 The engine or propeller generates torsional vibrations in the drive unit which produces a hammering noise in the transmission.

14.1 Mount a flexible coupling with a different stiffness factor between en-gine and transmission; a coupling with a higher stiffness factor might be sufficient. Otherwise analyze the torsional vibrations to find out the re-quired stiffness for the coupling.


If your damper plate is OK (no loose springs), perhaps a flexible coupling might help mitigate some of the noise. Just a thought
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Old 03-14-2017, 09:34 AM   #8
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With the Kansaki gear that I had on my Yanmar 3cyl 12-15 yrs ago I only had the problem when the gear oil got fully warmed up. Comming back to the marina I was embarrassed. Sounded like the trans was falling appart.

At first I used heavier oil. Hardly made any difference. Then I used ATF and 90W gear oil mixed. Better.

Eventially I installed an oil pump and an oil cooler. Used the drain hole and the fill hole for circulation. Used a mix of gear oil, synthetic gear oil and some ATF. That did fine. Almost quiet.

Ran the boat for about 4 years after that and suffered no downsides. Other than the expensive oil pump. It was a 32V unit all made of bronze. It ran slow of course but that was ideal. Do'nt remember what I used as a cooler. I think it was a very small unit like a typical oil cooler. Probably hooked it up w a seawater intake hose. No more clatter though.
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Old 03-14-2017, 10:14 AM   #9
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I think Volvo had a rash of ZF 25 (they rebrand them MSS 25) failures behind their D2s. Not sure if it was infant mortality or what. I have the same box with a different ratio, and no issues yet.
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Old 03-14-2017, 10:20 AM   #10
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I think I saw an upgrade to use a different damper plate. I should mention that I have a flexible coupling that the PO installed, that I kept during the repower. I think he did that when he took out his previous gear behind the BMW engine. But he trolled a lot.
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Old 03-14-2017, 02:19 PM   #11
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Thanks for the suggestions, guys.

Yup - I'm in agreement about the noise being caused by torsional vibration.

I did add a flexible coupling when I did the re-power. Hard to say if it has helped the issue as I installed it when the package was new.


The gearbox also came with a cooler so it doesn't see very high temperatures, although it is quieter idling out of the marina in comparison to idling back in. I am thinking that the noise could be slightly higher recently just due to hot weather.

I guess this is one of the negatives of new lightweight engines. I should have kept the big heavy flywheel off the old Volvo MD17 and bolted it on the Vetus

Here's the flex coupling I have installed.
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Old 03-14-2017, 02:37 PM   #12
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Quote:
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I think Volvo had a rash of ZF 25 (they rebrand them MSS 25) failures behind their D2s. Not sure if it was infant mortality or what. I have the same box with a different ratio, and no issues yet.
I did read about some ZF issues when deciding on which gearbox to use. In the end I decided to go with the down angle of the 25A to keep the engine somewhat level. Vetus was recommending the 15A but I decided to go one step up to the 25A (bigger is always better?). Maybe that wasn't such a good idea.

I also noticed that the ATF capacity of the ZF-25A is much less than the ZF25.
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Old 03-14-2017, 03:00 PM   #13
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Auscan,
I had a much more flexable coupling than the orange guys. And I changed my damper plate to one that had white plastic wedges instead of springs.
Sorry I should have mentioned that. Both the aforementioned items worked good. I think it was an RD coupling.

Re the 25A to 25A that probably was a good move. You may only have half the ratteling that I had.
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Old 03-14-2017, 03:47 PM   #14
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Read this thread from 2013


http://www.trawlerforum.com/forums/s...tes-11198.html
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Old 03-14-2017, 10:53 PM   #15
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Maybe I will shop around and see what is available for damper plates. I can then pull the gearbox and have a look at it. If it looks fine, i'll have a spare which probably isn't a bad idea.
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Old 03-27-2017, 11:47 AM   #16
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I had a ZF without a flexable coupling, connected to my 6,5 L Gm V8 diesel, and it rattled at lot, under 800 rpm, so I avoided to drive lower than 800 rpm, worked for me in the six years, I drove the boat. This was in my Coronet 31, and I'm shore it won't be a problem for the next owner. Lowest speed without noise, was 4,7 knots.if I wanted to drive slower I djust put her out of gear.
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Old 03-28-2017, 01:58 AM   #17
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Quote:
Originally Posted by C lectric View Post
Could be the damper plate failing. It attaches to the engine flywheel and drives the gear input shaft often using springs for pulse and shock absorption. Eventually the springs fail and break. That can cause the noise and if left will fail completely leaving you without drive.
One possibility.


Bingo!

I pulled the gearbox today and had a look at the back of the damper plate. It was a Centa DS damper plate. They don't have springs or roller pins like some. Just rubber bumpers. One set for low power dampening and another set for high load dampening. Guess what... the low power bumpers were flogged out.

The Vetus dealer will have a new damper plate for me tomorrow under warranty. I should be ready to go again by the weekend. Woohoo!
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Old 03-28-2017, 01:58 AM   #18
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Congratulations 🎊
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Old 03-28-2017, 04:24 AM   #19
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Quote:
Originally Posted by AusCan View Post
Thanks for the suggestions, guys.

Yup - I'm in agreement about the noise being caused by torsional vibration.

I did add a flexible coupling when I did the re-power. Hard to say if it has helped the issue as I installed it when the package was new.


The gearbox also came with a cooler so it doesn't see very high temperatures, although it is quieter idling out of the marina in comparison to idling back in. I am thinking that the noise could be slightly higher recently just due to hot weather.

I guess this is one of the negatives of new lightweight engines. I should have kept the big heavy flywheel off the old Volvo MD17 and bolted it on the Vetus

Here's the flex coupling I have installed.
I am interested in your split coupling attaching to the prop shaft behind the red flex coupling, who makes that?

I am planning to get one like that
Are they available for velvet drives?

Buck Algonquin is one type I found, does yours completely split in half?
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Old 03-28-2017, 05:55 AM   #20
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My shaft coupling was made by the same local company that made the flex coupling.

Poly Flex Group - Advanced Polymer Technology for Vibration Control - Steel Shaft Couplings & Spacers

They make them to suit most transmission flanges. Just measure up the diameter, bolt circle, etc.

I've never seen one that completely splits in half; the flange is always in one piece.
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