Hurth / ZF M15A Transmission Failures

[ribbony]

Honey, while you are there will you change the oil and scrub the bilge !

[delmarrey]

Originally Posted by 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.

It went 27 years without a cooler but I have closed up the engine compartment a bit tighter. So the fresh cool air is just a precausion. They cast on cooling fins to help with cooling.
As for a cooler, this is a ZF10, which has no holes for a cooler or a way for the oil to flow through a cooler. It only takes .5 lt.

[tomj]

The latest in a long story of failed Hurth/ZF 15MA (8 deg down angle) transmissions installed on a Phasor P4-37-05 37.5 HP 4Cyl. engine. We were on our 2nd day of our second Bahamas Cruise, having arrived in Mill Creek in Hampton VA about 2 weeks ago. While maneuvering into a slip at the Ft. Monroe Marina, at Old Point Comfort, we had the third transmission failure (Hurth/ZF 15MA trans)! This transmission only had about 225 hours on it when it would not go into forward gear. This transmission replaced one that failed in April 2007 while we were on our way back from the Bahamas - near Savannah, GA. Reverse seemed to work OK, but it wouldn't stay in forward. Checked linkages, etc, but all seemed in order. Placed a call to Hurth/ZF in Stevensville, MD (near Annapolis), and they agreed to replace it under warrantee, and even agreed to send a tech down to Hampton to do the work. The tech found nothing wrong with the installation, the engine, damper plate, alignment or anything else.

They have no answers regarding why we are having so many failures of this transmission (the original trans lasted about 300 hours and was replaced under warantee - removal and installation by owner - me; the second transmission lasted about 600 hours but was not covered under warrantee - we 'ate' this one - and did the removal and installation ourselves; the third one just recently failed at about 225 hours and was removed and replaced under warantee at no cost).

The new trans went in easily and we now have about 12 hours on it having returned the boat from Hampton to our dock in Kinsale, VA yesterday (10/31/08). We decided to 'scrub' the Bahams cruise for this year as we have about "0" confidence in this piece of machinery, as although our boat is a 'sailboat', one DOES need a reliable source of power when transiting the ICW, coping with current in GA, bridge openings, etc.

We are now considering replacing the Hurth/ZF unit with a "Twin Disc" unit - but need to research what the conversion/mating will entail.

We would be interested in hearing of other Hurth/ZF 15MA transmission failures.

Tom in Kinsale, VA

[Stillraining]

Simple Solution

Less motoring more sailing... Just kidding

Wow unbelievable luck..mine jumps into gear a little also but I will run it till it fails me..I have no way of knowing the hours on it as there were no log books with the boat when we bought it.

I personally have never heard of your level of bad luck with the 15...I shurley understand your frustration at this point..FWIW I have heard of problums with twin disks as well so dont know what the solution is.

Are you waiting a couple seconds like "3" to let your prop quit spinning befor reversing directions?

We have learned that Plymoth van trannys will last twice as long if you dont shift them while still moving no mater how slowly..come to a compleat stop then shift it.

[tomj]

If only the 'simple solution' was always available......

Thanks for the reply. After 3 failures, we've done just about everything we can think of to 'help' this transmission to not fail. We are very conservative in the shifting as you recommended, change the trans oil at every oil change, ensure full throw of the shift lever through the 'detents', always shift to reverse immediately when sailing, installed the optional trans cooler (actually a raw water 'heat sink' which bolts on the side of the trans).

The ZF tech (a quite knowledgeable person) who did the installation on this trans told me that if everything is working correctly on this trans, there should be very little heat other than the small amount of bearing heat (meaning if the clutch plates 'lock up' correctly), there will be no heating problems. Makes sense to me!! I have a IR thermometer, and I've 'shot' it numerous times (under load) which revealed a case temp of about 125deg F, which is about the same temp as the rest of the engine assembly. When I mentioned this to the tech, he indicated that wasn't too high.

A post mortem by ZF of this transmission supposedly showed little wear on the clutch plates, but did indicate some 'off center' wear which the tech thought might mean some internal mis-alignment within the trans itself - ZF was planning on sending the internal parts and the trans to ZF in Italy for evaluation........

One thing that we did notice for several months on the last trans before it failed was that at about 1000 RPM, the engine seemed to 'miss' (seemed to run a bit rough), but would quit if the RPM was increased slightly. I thought that perhaps, I had a slight injector problem at that RPM. Actually, now it appears that the trans was alternately and rapidly going in and out of gear at that RPM, suggesting that the 'servo' balls/springs were beginning to fail, and that additional torque was required to 'lock things up' in the clutch assemblys. The tech more or less agreed that that was a possiblity, but supposedly, the 'post mortem' didn't reveal any (abnormal) wear in this area.

Anyway, I've beat this to death!!!

Thanks again,

Tom in Kinsale, VA

[Stillraining]

Originally Posted by tomj

Anyway, I've beat this to death!!!

Thanks again,

Tom in Kinsale, VA

For your sake my friend...I truly hope you have this time...Good luck

[NCboatrx]

The failures that you are experiencing may be caused by the type of damper plate that is on the engine's flywheel. Some engines have characteristics that can shock the transmission. We have had great success with the R&D drive plates as well as the Penta ones.

Regards, Stanley

[Cheechako]

it sounds like you might be over propped. I've found the Hurth to be very reliable on several boats. They get super hot, I mean way too hot to touch. I considered the oil cooler on one of my boats but never did it and never had a problem. I wish they made an oil coller plate you could pump water through, that would be nice. Always wanted to try about 20 ft of soft copper tubing wound around the case and a small pump! My Passport 47 had an 85hp Mercedes diesel and a Hurth V drive. That tranny was very small and was the hottest of the bunch. Never failed though.

[Cheechako]

My buddy has put two Velvet drives in his boat in the last ten years... those things are huge...just an FYI. Yours sounds like a bad batch of trannys to me... If you took your last bad tranny to have it rebuilt, I wonder if the mechanic could tell you if the thing was not bored correctly or something like that?

[Stillraining]

FWIW Im Running a 17 x 17

[tomj]

I've been running a 14" x 11" prop. Don't think I'm over propped as I get hull speed at about 2000 rpm (where the torque and fuel curves meet), and can just get full RPM with full throttle with no black smoke nor overheating (with a clean prop and bottom).

[cooper]

nah not over propped 18 inch and 13 pitch with 50 hp is still within their leisure duty cycle. Still with the number of failures it is outside "statistics" which (and I have no idea where) would make me want to look for an answer apart from just transmission failure. The oddness of your situation would make me uncomfortable about any transmission until I worked out what was going on. Do you have a flexible coupling between your gear box output flange and the prop shaft ? How many bearings do you have on your prop shaft ? What prop seal are you using ? (just for my own curiosity and theory's)

cheers

[tomj]

Thanks for the comeback! Yeah, I'm looking for other "reasons" for failure, specifically the damper plate. I think it might be too "stiff" and am looking at alternatives (such as the R & D 2-stage plates sold by PYI). We do have a flex coupling between the trans output shaft and the prop shaft. The prop shaft itself is relatively short (less than 2', and has one cutless bearing in the shaftlog deadwood - the boat is full keel) and has a conventional stuffing box (attached to the shaftlog via a flex hose and hose clamps). No unusual wear on shaft coupling, stuffing box or cutless bearing - which is NOT the problem.

Phasor hasn't been much help....

[Stillraining]

Well one consultation tomJ...we will be all comming to you for advice as you will become an expert on these things befor your done..Sorry mate..just trying to put a little sunshine in your day.

[tomj]

Originally Posted by Stillraining

Well one consultation tomJ...we will be all comming to you for advice as you will become an expert on these things befor your done..Sorry mate..just trying to put a little sunshine in your day.

Thanks for the note! I've been in "consultation" with several folks from Phasor, Beta Marine, and PYI and have just about come to the conclusion that the problems have stemmed from the damper plate, which is not 'flexible' enough to absorb the torsional impulses of the Kubota engine. Looking at replacing the damper plate with a more 'flexible' unit.......