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sgtPluck 24-04-2011 05:37

Hurth ZF10 Slipping
I have a rebuilt Hurth ZF 10 with around 300 hours on it. It has always rattled a small bit at low revs. Yesterday as I increased revs from idle to 1500 or so I felt like it slipped, because I heard nothing and then a 'clunk' which I guess was it engaging properly.
I checked to see that it engages immediately in forward and reverse (per the troubleshooting instructions in my Calder book) and it does. I have not changed the oil yet but I will.

I'm in Georgetown in the Bahamas, about to set off for the Dominican Republic (probably lots of motor sailing.) I'm really wondering whether it is alright to keep going with this, or do I need to get it taken care of before I leave.

sgtPluck 24-04-2011 08:07

Re: Hurth ZF10 slipping
I checked the oil, the level is fine. The oil is a little bit brown but not much and it does not smell burned.

delmarrey 18-06-2011 17:34

Re: Hurth ZF10 Slipping
1 Attachment(s)
I know this may be a bit late but someone else could use the info.


Tynesider 21-06-2011 12:45

Re: Hurth ZF10 Slipping

I Have a similar problems and just removed my Hurth -100-2R gearbox and replacing it with rebranded ZF10 M.

The bad news is it is probably your drive/damper plate infront of the gearbox, but to replace a drive/damper plate without a new gearbox is very unwise as for sure the gearbox will be the next problem so I am replacing both at the same time.

It's not rocket science to get the gearbox and plate out.

Like you once the boat was in gear she will go forever, BUT, do I want a faulty gearbox at sea or coming into a marina? NO WAY!!

Hope this helps

Mike :thumb:

sgtPluck 21-06-2011 14:10

Re: Hurth ZF10 Slipping
Hi Mike,
I'm back in Ft Lauderdale working on the problem. I got a new ZF 10m shipped to Georgetown and installed that there. Then sailed all the way back here to keep hours low on it.
This latest one is my 3rd transmission. When the first one failed we thought the damper plate could be the issue, so installed a 'fancy' new damper plate with the 2nd gear. It still failed, and the damper plate looked fine when I took it off in Georgetown.
I am having 1" of pitch taken off my prop, in the hope that this might solve the problem. I was about 100rpm off max engine rpm with the existing pitch. Most people I've spoken to don't think this is enough to cause the problems I've had, but some do. It's pretty cheap to get the prop modified, and I've pretty much ruled out the other possible causes I can think of.
Hopefully this will be it. Other ZF owners have also suggested to me that you need to change the oil in these gears more frequently than the manual suggests (I'm going to do it with my regular engine oil change.)

Good luck, I hope you don't have recurring problems like I did. It is a real pain in the arse getting that gear on and off the engine (at least it is on my boat.)

Dynamo1181 21-06-2011 19:10

Re: Hurth ZF10 Slipping
I was told by a certified Hurth rebuilder to use type F transmission fluid as it has more "bite" and will help reduce any tendcy to slip. I have used 50/50 Dexron and type F for 6000 hrs without issue. I change the fluid every other engine oil change as well as prior to any layup.

Tynesider 22-06-2011 08:51

Re: Hurth ZF10 Slipping
More Food for thought!

Sounds as if your making headway.

Please don't take offence but 'I assume' you know there is a slight differance from the old Hurth gearbox to the ZF box in the gear ratio.

Are you having trouble with the reduction ratios. I suspect your old gearbox has an ahead reduction of 1.79:1 where as the latest ZF10M box have a reduction ratio of 2.05:1.

It doesn't sound much, but it does have a rpm differance on the shaft at maximum speed. If your propeller is correctly sized you can achieve maximum revs, then fitting a ZF10M will result in a slower boat,on the otherhand, if your boat is 'over prop'd' you might notice an improved performance.

Good luck :thumb:

delmarrey 22-06-2011 09:23

Re: Hurth ZF10 Slipping
Actually, the ZF 10 comes in multiple ratios >> Simplicity Marine Drives - Hurth/ZF Transmissions & Prices

As well they have duty ratings.


Originally Posted by HURTH
Duty Definitions
Duty Ratings

Highly intermittent operation with very large variations in engine speed and power
Average engine operating hours limit:
500 hours/year 300 hours/year for mechanical gearboxes
Typical hull forms:
Typical applications:
Private, non-commercial, non-charter sport/leisure activities.

Intermittent operation with large variations in engine speed and power
Average engine operating hours limit:
2500 hours/year (for hydraulic gearboxes smaller than the ZF 650 series, 2000 hours/year).
Typical hull forms:
Planing and semi-displacement.
Typical applications:
Private and charter, sport/leisure activities, naval and police activities.

Intermittent operation with some variations in engine speed and power
Average engine operating hours limit:
4000 hours/year. 3500 hours/year for gearboxes smaller than ZF 2000 series and workboat ZF W2700 series.
Typical hull forms:
Semi-displacement and displacement
Typical applications:
Charter and commercial craft (example: crew boats and fast ferries), and naval and police activities.

Continuous operation with little or no variations in engine speed and power
Average engine operating hours limit:
Typical hull forms:
Typical applications:
Heavy duty commercial vessels, tugs, fishing boats.

sgtPluck 22-06-2011 09:57

Re: Hurth ZF10 Slipping
Yeah, my current gear is 2.0.4:1, so was my original ZF10m, the 2nd gear I had in there was a HBW100 at 1.79 so if I am over propped the issue would have been exacerbated with that second gear.

I still don't fully understand their duty definitions. Because medium duty as defined, equates to 9.5 hours a day of use. I certainly didn't put 3,500 hours on the engine, but I definitely put more than 9.5 hours of use on it at a time. Up to 29 hours at one point when I was becalmed. Implied in their definitions is that cumulative use is what matters, but running my boat in 'continuous duty' mode for a few days is ok?

I am deliberately under-propping now. I don't know if it will fix it, but it's the last thing I know of that I can try, save installing a different unit. I'm willing to give up a bit of motoring boat speed. I also will avoid the ICW or other places that require motoring as much as I can.

Fingers crossed and a prayer to the engine-gods that it will work.

delmarrey 22-06-2011 20:53

Re: Hurth ZF10 Slipping
Basicly, one would go up one size in trany to upgrade to the next duty. It's rated by HP & RPM >> ZF Marine Transmissions, ZF Hurth Marine* ZF 10 M, ZF Marine Transmissions, Hurth ZF10M Transmissions at Trans Atlantic Diesels

So, if you went to a ZF 12 or 15 it would be a stronger trany. You just have to find one with about the same gear ratio or re-prop the system.

Maxs 28-07-2011 20:30

I heard from a marine engine manufacturer that since ZF acquired Hurth, they changed the company that makes the clutches, and they are not that good. They stopped selling the engines with those transmissions. They are now using. Twin disc. Same foot print, same shape, measures, design and looks, but way better. The only noticeable difference is that the shifter is on the opposite side.....
Not a single complaint call from the new ones since they started installing them.....

oldcal46skipper 29-07-2011 04:32

Re: Hurth ZF10 Slipping
Among folks who repair marine reversing gears, Hurth/ZF gears are known as $1 per hour gears. They cost about $1,000 and last about 1,000 hours.
I do not rebuild them anymore as the parts and labor just about equals the price of a new one.

Dynamo1181 29-07-2011 05:25

Re: Hurth ZF10 Slipping
6500 hrs on our Hurth gear/4108 and still going strong! I have experienced no issues and attribute my good experience to the attentive maintenance.

balimara 08-08-2011 13:28

Re: Hurth ZF10 Slipping

Originally Posted by delmarrey (Post 711047)
I know this may be a bit late but someone else could use the info.


Hi delmarrey,
yes, I could use this information and want to thank you this way. My Hurth ZF10 was slipping and with your nice table I was able to get it working again. The diesel "rinse and run" was working perfect. :thumb:

delmarrey 08-08-2011 14:00

Re: Hurth ZF10 Slipping
Happy it worked out for you!

If anyone's interested, I have a pdf copy of the repair manual and partial parts list of this tranny. Different gear ratios take different gears.

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