Hurth / ZF M15A Transmission Failures

[Steve Pope]

I too have seen off my last ZF box, I opted for a PRM 150 hydraulic box and so far am not disappointed, Had a bit of work to do to modify the engine beds but while I was at it I fitted a python drive CV joint set up which takes all the guesswork out of alignment. May your twin disc never give you the grief that the ZF did.

[tomj]

Through 5 transmissions, and approximately 1600 engine hours (not all underway - i.e., battery charging, etc), we have 'religiously' kept the trans in reverse while sailing. We even have a small 'dymo' marker notice on the Edson pedestal which cautions about leaving the trans in 'forward' while sailing (or when anchored in strong current)..

The trans fluid was changed an all the failed transmissions with every engine oil change at approximately 100 hr intervals!

There were no problems due to the installation (alignment, etc.) which was verified during the 3rd failure by a Hurth rep (from Annapolis) who installed a new trans under warrantee.

What we've determined (very difficult to actually confirm) is that the Hurth trans is 'vastly overspec'd' inasmuch as it's simply not robust enough to handle the output of the 38HP Kubota engine, although the engine output (torque, HP, rpm etc. do not even approach much less exceed the limits specified by Hurth for pleasure use/heavy duty use/continuous use.

Additionally, there are probably some design problems such as a less than adequate thrust washer and not terribly robust clutch discs.

Hurth can give no explanation other than to say "There's something wrong with the installation on your boat......."

We can beat this thread to death, but I'm moving on and enjoying my boat with a Twin Disc replacement for the Hurth!

Tom in Kinsale, VA

[cburger]

Hurth gears have a reputatin of being very robust. Individual gears are designed to be utilized for a specific HP and RPM range of motor. The Hurth manual also states when a specifc gear is used with a specific HP rating that their bolt on cooler is supposed to be used. It also states that a flex coupling should be utilized as well. Finally proper propeller size and pitch are important for longevity of the gear.

[Machinist Gary]

I have rebuilt our Hurth Z drive on our C&C Landfall 38 12 years ago and I noted that there is a thrust washer which assists engagment on the counter rotating clutch shaft. My thrust washer was worn out (800 hrs). If you allow this transmision to freewheel in forward or neutral while sailing, the prop will apply back pressure to this sinter bronzed thrust washer and soon wear it out, resuting in to much play in the clutch shaft assembly and then it becomes no Shifty time. You can rev the motor a bit to get the clutch pack to ramp up tight but keep freewheellin these trannys while*sailing and you will be back to the shop. I carry the spare clutch plates (never needed) and a couple of new washers (2000 hrs and still locks up nice at idle). Once sailing with the motor off, shifting to reverse results in a slight clunk as the clutch ramps lock it up. I now sail with a Max Prop but I still notice it requires a shift into reverse to stop freewheeing even after the prop feathers.
Gary http://www.cruisersforum.com/images/...s/banghead.gif

[RBEmerson]

FWIW, we've now got two trips from the Chesapeake to the Bahamas and back (wound up moored, in Man O War Cay, next to Tomj!) and our tranny is doing fine. We put in tons of time motoring in the ditch and offshore (e.g., Ft. Pierce - Fernandina, Fernandina - Charleston - 170 hours from Vero Beach to Deale, MD alone) as well as four crossings to and from Abaco. And we took one direct hit to the prop - in the Alligator-Pungo Cut we tagged a log hard enough to ding one blade tip. After all this, our ZF tranny is working like a charm.

We had major engine location problems (the block was much too high relative to the prop shaft) that prompted kludged work-arounds that caused the engine and prop shaft to drop out of line, killing our first two transmissions. With the engine lowered 1" in its mounts, it's now possible to get everything in alignment and keep it there. End of problems.

[darcoboss]

Originally Posted by tomj

All I get from Hurth/ZF (Annapolis office) is they don't have any history of failures.....(surprise/surprise)...

Am considering adding the (optional) oil cooler which simply bolts on the side of the trans using heat transfer of the aluminum case. In the meantime, I am using the engine compartment blower to evacuate hot air from the area of the trans. May consider using synthetic oil - thanks for the response.

you MAY WANT TO TAKE INTO CONSIDERATION THAT YOUR PROP IS TURNING YOUR REAR SHAFT, AND IT MAY NOT BE HOOKED TO A PUMP, THEREFORE WEARING YOUR CLUTCH CONSTANTLY..... THINGS YOU ARE NOT TOLD.....SAILING MAKES YOUR PROP TURN YOUR OUTSHAFT.....

[Svsilvergirl]

Yikes , help here , I have a 44 islander with a 4108 & a vurth transmission , and a v drive gearbox . When sailing out definitely sounds the shaft . The previous owner said this its not a problem . I tried putting it in neutral and forward , with no change , shaft spins just as if you were motoring . infact its quite noisy . I had considered trying to mount an alternator to take advantage of this . But from what I am reading here this could be damaging the transmission ? We have only owned the boat for one summer , and the motor is newly rebuilt and the transmission is new . Truly don't want to make a bonehead mistake here and burn up a transmission , just because I didn't know any better.........

[Svsilvergirl]

Sheesh , tiny keyboard . Hurth transmission , and definitely spins the shaft while sailing.......

[DeepFrz]

Spinning the shaft should not be a problem, however if it is noisy and bothersome you might want to attach a shaft brake. They are like auto disk brakes mounted on the shaft. If you do that however, you need a fail safe way to ensure the brake is disengaged before putting the transmission in gear.

Also (because of the noise) you may have a bent shaft that is causing the noise so check that the shaft is not bent and the prop is nicely balanced.

Something like this although if you search "shaft brakes" you will find there are many brands.

Shaft Brakes

[highseas]

Hurth specifically says to leave in REVERSE when not in use and underway.

[tomj]

I NEVER SAILED WITH THE TRANS NOT IN REVERSE - IN ALL THE YEARS WE OWNED AND HAD FAILURES OF THE hURTH!!!!!!! END OF STORY! I HAVE 2 HURTH GEARS (ONE WITH NEW CLUTCHES AND THRUST WASHERS - THE OTHER NEEDS CLUTCHES AND THRUST WASHERS). THINKING OF MOUNTING THEM ON TOP OF A BIG LEMON! WE ARE ON OUR WAY DOWN THE ICW (AGAIN) WITH A TWIN DISC TRANS WHICH (SO FAR) IS WORKING FINE!

TOMJ ABOARD SHEARWATER IN MILE HAMMOCK BAY, NC

[DeepFrz]

Hurth specifically says to leave in REVERSE when not in use and underway.

highseas, can you provide a link to that information?

[Maine Sail]

Originally Posted by DeepFrz

highseas, can you provide a link to that information?

Hurth / ZF says Neutral OR Reverse. Just not the same position as the direction you are sailing meaning NOT forward.

Image Courtesy C-34 Association



Here's a more recent statement saying exactly the same thing from ZF Marine..

ZF Gear Position Statement

[Svsilvergirl]

Just called a hurth service center , and they confirmed should never sail with trans in forward our reverse . Said putting in reverse should stop shaft from spinning . Haven't been anker to try this yet . Butt out will be nice if this does stop shaft from spinning, . Made quite about of noise . not bad noises , just sounded like there was a motor spinning or something......

[Blue Stocking]

I know of one boat which knocked out 2 Hurth HBW150 boxes.
Turned out that the damper plate was about 10 thou off center, and was side loading the input shaft.
The damage was being done while motoring. Had nothing to do with the sailing thing.