Hurth / ZF M15A Transmission Failures

[tomj]

Seems like I started this thread way back in the spring when I replaced the Hurth 15 MA (8 deg. down angle) on my Phasor 37.5 Kubota based engine for the second time in less than 1000 hours engine time. Since the first post on this thread, I have done the following: Added the optional transmission cooler (actually a heat sink which bolts onto a machined flat surface on the port side of the trans) which uses 'raw' water before it reaches the engine heat exchanger-as depicted in the Hurth supplied drawings. Also have changed from Dexron III ATF (as recommended by Hurth) to Amsoil synthetic Dexron III equivalent ATF fluid (I had contacted Foley in MA regarding their expounding the merits of their synthetic trans oil for the Hurth, but refused to pay $45 per quart as opposed to about $9 per quart of Amsoil synthetic ATF). Also, have increased the engine compartment cooling a bit by adding an additional fresh air blower to direct fresh (and cooler) air to the engine compartment (we have an 1975 Alberg 37 MK-II yawl which has a relatively small engine compartment). We've had no problems with this 'new' transmission (so far) and have about 150 hours (engine time) on the new installation. Regarding the addition of the trans cooler, by all Hurth specs, the cooler is not required due to the hp rating of the engine, and the usage of the power train, but we added it to be on the safe side. Subsequent checking of the transmission operating temperature using an IR thermometer (with laser pointing device) indicates the temp of the trans case is in the neighborhood of 125 - 130 deg F, which in our estimation is not terribly high. We are also aware of all the other questions/posting on this thread regarding duty cycles, etc. etc. etc. etc...... which we have never exceeded..... If this trans fails prematurely following all the precautions which we have taken, we will have to realize that the Hurth 15 MA transmission is a piece of "junk" (politely said - would rather use much stronger language!!!) and will (at great expense) be forced to resort to a different brand of transmission, such as a 'Twin Disc" etc. Hurth has been great at providing a new replacement transmission (at about 2 LARGE Boat Units) in a timely manner - less than one day), but they seem to disavow that there have been problems with this transmission. CAVEAT EMPTOR Perhaps see you in the Bahamas next year...... and thanks for the interest!

[Alan Wheeler]

I look forward to future reviews of how things are going. Thanks for your update.

[S/V Antares]

Tomj... Can you elaborate on the failure mode? Bearings, Slippage? "Bang" or slow death? What RPM could you reach at WOT in gear? Did you dump the gears or disect them?

The ZF15 is a good sized box with big bearing and rated to 55kW (76hp) so the appliction is well within the range.

130 Deg. F is very cool even on the outside of the box. The Phazors are painted white. If the gear is white your IR reading will be a few deg. off (Cooler) but still very cool fore a gear.

Given your experience and Foley's advice I think I will switch to the syn trans oil.

Will

[tomj]

The indications on the first (original zf15ma) was that on cool fall mornings, it was becoming difficult to initially engage forward gear and we found we had to 'rev' the engine to get the trans into gear (with a resounding 'clunk' when it finally engaged). It seemed to be ok when the trans was up to normal operating temp. However, after several occurrances of the cool start problems, along with the slow engagement indications, the trans would sometimes 'jump' out of gear and then after a second or two with an increase in engine rpm, the trans would re-engage, again with sort of a clunk. After several occurrances, we decided to return home (from the Oxford, MD area back to Kinsale, VA as we didn't want to push our luck with an obviously unreliable transmission - a total of about 13 hours operating time. I subsequently swapped the original 15 MA for new one from ZF (still under warrantee).

The second occurrance was this spring in GA on the ICW returning from the Bahamas. We were motor sailing and noticed that we were going slower and slower (there was a good amount of current against us, (but not 3kts). There was no other indication of a slipping transmission - no noise, nothing..The engine didn't even increase rpm noticibly, but I did notice the engine coolant temperature had decreased very slightly (less torque on the engine). We thought the prop coupling had sheared, or that we had lost the prop. Further investigation after we anchored indicated that the trans was putting out a slight amount of forward torque, as we could move forward a bit, but still no noise, etc. Reverse gear seemed to work OK however. (This transmission had about 600 engine hours on it when it failed.) We subsequently were towed about 15 miles to a 'do it yourself' marina where I replaced the transmission with a new one (not rebuilt) which was shipped within about 18 hours by ZF from Ft. Lauderdale. By this time I'm getting pretty good at swapping out transmissions on this setup (about 5 hours to remove and replace). Still have no idea of why both trans failed (and neither does ZF, or at least that's what they told me). When I returned the original (first failed trans) trans to ZF in Stevensville, they supposedly tore it down but couldn't 'find anything wrong' with it....... We now have about 175 hours on the currently installed transmission and so far so good..

[brian and clare]

http://www.cruisersforum.com/gallery...p?i=3689&c=517

Hi, I finally got the photo of that transmission. Its a horrible one to say the least, but if anyone can verify this as a hurth I would very much appreciate it.

Thanks
Brian

[Steve Pope]

Yup, I would say it's a Hurth.

[never monday]

Originally Posted by brian and clare

http://www.cruisersforum.com/gallery...p?i=3689&c=517

Hi, I finally got the photo of that transmission. Its a horrible one to say the least, but if anyone can verify this as a hurth I would very much appreciate it.

Thanks
Brian

I'm not as confident that's a Hurth. The radius of the case sides is too much and I don't see the case half seam. There is an ID tag on the top visible in the pic. Can you get more pics?
t

[delmarrey]

This is a hurth!

[Alan Wheeler]

Yep that's a Hurth Brian.
Hey you been getting my emails???

[ribbony]

That ZF gearbox is the one we were thinking of as ideal for our vessel. That is not a comforting story about the ZF15MA boxes. Two things we gained from the discussion here that we would do with a gearbox is use a good oil and install a fan blowing on the box directly wired to the engine output so when the engine is running the fan is blowing.

[Steve Pope]

unless the fan was drawing air from somewhere other than the engine room I doubt it would help much. The bolt on (heat sink) type will be more efficient. Also synthetic oil is definitely the way to go, I use redline and so far have no reason to doubt that it is working well. regularly checking the colour of your oil is an easy check to make. Dirty oil is generally caused by overheating, if it retains its normal colour and reasonable clarity I would consider it OK.

[delmarrey]

Originally Posted by ribbony

Two things we gained from the discussion here that we would do with a gearbox is use a good oil and install a fan blowing on the box directly wired to the engine output so when the engine is running the fan is blowing.

That's my set up, but I have a toggle switch at the helm. If I'm just putting around at low RPM's the fan is off. If I'm at crusing speed then the fan is on. And the fan draws from a scoop/cowling on the transome top.

The Jabsco fan I have is suppose to last 1000 hours. I figure that is cheap ($125) compaired to a tranny and the labor involved.

[Alan Wheeler]

Well Del, you no fool when it comes to engineering. But seriously, I would be considering heat exhanging. A water cooled unit would be best, or at the least, a small air cooled oil cooler. Even if it is just to increase the oil capacity in the system. Air cooling the box may help, but I doubt it will be that big a help.

[tomj]

Will be wrapping up the sailing season soon on the Chesapeake Bay - the status of our 3rd ZF is that it's still working fine. We've added the optional bolt-on water cooled heat sink, and along with an in-line cooling blower which directs outside air to the transmission along with a regular bilge blower which sucks warm engine compartment air to the outside, hopefully we can get some long term service from this 15MA transmission.

[S/V Antares]

Sure looks Hurth/ZF to me. It is not so bad a job getting them out. With the adapter plate on the belhousing it should be "Easy"

Gets tough if the shaft cannot be pushed back 2".

Here is a picture of my wife taking our ZF10 out. I keep telling her i cannot get back there. So far it works!