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Hurth transmission diagnosis

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
The original Hurth transmission on my M25 is apparently at the end of its life after 1800 hours. I put about 50 more hours on it on the Hawaii cruise, not including running in neutral 40 minutes a day to recharge 15 or so amp hours.

The symptom is a squealing noise occasionally in gear above 1500 rpms, which is relieved by reducing throttle and resetting to 1400 rpms. The throw of the trans lever is good and and the fluid has been maintained correctly during my ownership. I always sail with reverse gear engaged.

What is the cause of the squealing noise? Why is it unpredictable? Is there any ambiguity in the diagnosis of new-tranny-needed? I ask because of a Frank Langer experience posted two years ago:

I had the same sound with our Hurth transmission, the grinding sound coming without warning. I would immediately shift to neutral, then back into gear and it would be fine until it happened again, sometimes within 5 minutes sometimes an hour later--very unnerving. The fluid level was correct and looked fine, but it still happened.

I replaced the Hurth with a Twin Disc transmission and it has been working well, though the same sound has occurred on two separate occasions, both when motoring in rough seas.
 
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Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Much discussion on this, and conflicting recommendations. The idea of reverse is to stop the shaft turning, which (they say) can polish the transmission surfaces.

Equally energetic disagreements about whether a spinning prop slows you down or speeds you up--while either destroying your transmission or preserving its life.
 

Rick R.

Contributing Partner
Much discussion on this, and conflicting recommendations. The idea of reverse is to stop the shaft turning, which (they say) can polish the transmission surfaces.

Equally energetic disagreements about whether a spinning prop slows you down or speeds you up--while either destroying your transmission or preserving its life.

When ours started acting up I had it rebuilt. A total waste of money. Thankfully, the shop that did the rebuild gave me a brand new tranny for free!

We leave ours in reverse while sailing as well.

PS The guy who works for Beta Marine out of the Carolina's told me when he was employed by Hurth, "THEY" called their transmissions the "Dollar per hour" transmissions because you could hope to get about that much time before it was shot. Not very inspiring.
 
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Rocinante33

Contributing Partner
Christian,

When my Hurth went bad it did not make the screeching sound that you and others have described. It just would not move the boat when forward was engaged. Or it would move the boat very little. I would shift out of gear when it happened, then back into gear. Perhaps it would then catch any away we would go........or not. It was only in forward that it was an issue. Reverse was fine. At one point I thought the folding prop was not opening but disproved that by looking at the propshaft and observing that it wasn't turning, or was turning very slowly even as the engine was revved up.

I replaced it with a ZF 10 with the boat in the water.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Well, if a new trans costs about $1800, I guess I have proved the "dollar per hour" theory. No complaints, actually, after 30 years service.
 

reflections

Member I
hurth trans.

we repowered with new universal 25 about 5 yrs ago. came with a hurth zf5. 125 hours later trans. silpped in forward. told it was only guarenteed 1 year & it was 3 mths over. replaced with zf10. lasted 125 hours & started slipping. got on internet & found a cite for them in mexico. to make a long story short zf sent a person to our marina & replaced it with another zf10. have about 250 hours on it & still running well. we have a 1987 32-300. engine is also running great. zf told us that the zf5 was to small for the engine. wonder why they came with that trany in first place? $$
 

reflections

Member I
hurth trans.

we repowered with new universal 25 about 5 yrs ago. came with a hurth zf5. 125 hours later trans. silpped in forward. told it was only guarenteed 1 year & it was 3 mths over. replaced with zf10. lasted 125 hours & started slipping. got on internet & found a cite for them in mexico. to make a long story short zf sent a person to our marina & replaced it with another zf10. have about 250 hours on it & still running well. we have a 1987 32-300. engine is also running great. zf told us that the zf5 was to small for the engine. wonder why they came with that trany in first place? $$
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Good grief. A replaced engine, a bad ZF5, then a bad ZF10, now a replacement.

We do not intentionally abuse our transmissions for the sport of it. I just don't get the endless litany of problems.
 
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Pat C.

Member III
I'm planning on switching to a 3 blade feathering prop over my 2 blade fixed one this coming spring, but threads such as these give me pause. I don't worry much about the engine handling it, but the additional force on the tranny is another story. Any thoughts?

When I look a the manual regarding these transmissions I see a resilient coupling involved, and I wonder how many of these noises/problems are related to that and not the transmission at all. Guess it doesn't matter though since you have to pull the tranny regardless.
 

Rick R.

Contributing Partner
we repowered with new universal 25 about 5 yrs ago. came with a hurth zf5. 125 hours later trans. silpped in forward. told it was only guarenteed 1 year & it was 3 mths over. replaced with zf10. lasted 125 hours & started slipping. got on internet & found a cite for them in mexico. to make a long story short zf sent a person to our marina & replaced it with another zf10. have about 250 hours on it & still running well. we have a 1987 32-300. engine is also running great. zf told us that the zf5 was to small for the engine. wonder why they came with that trany in first place? $$

If mine goes kaput I'd like to get the number of the ZF guy in Mexico!
 

Beezer

Junior Member
Dont bother with a rebuild. Buy another one, or better yet buy the replacement cone clutch type that is a direct replacement and not a Hurth. These things are garbage. If you get stuck in a pinch the word on the street is that you can pump out the box, pour some mineral spirits in theere run it for a little bit and then pump it out. My guess is that this deglazes the plates. This is only an "out in the wild blue and nothing to lose" fix. Wish I had known about it mid pacific when my second rebuilt failed. I rebuilt one on the cabin top and got one professionally rebuilt and both died in short order. Also check engine alignment. Rebuilds don't last.
 

Cory B

Sustaining Member
Assuming our hour gauge was correct when we bought our boat, it had about 1500 hours on the engine. We switched from a 2 blade fixed to a 3 blade maxprop, and have an additional 400 hours on it.

Our boat has a 24HP Universal 8424 (M30?) with a Hurth HBW-100 transmission - that might be a little heavier duty than some of the ones people are describing here. It appears to be original and so far hasn't shown any problems.

I'm planning on switching to a 3 blade feathering prop over my 2 blade fixed one this coming spring, but threads such as these give me pause. I don't worry much about the engine handling it, but the additional force on the tranny is another story. Any thoughts?

When I look a the manual regarding these transmissions I see a resilient coupling involved, and I wonder how many of these noises/problems are related to that and not the transmission at all. Guess it doesn't matter though since you have to pull the tranny regardless.
 
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Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Update:

There is nothing wrong with my 1800-hour Hurth 5 transmission.

This weekend we motored six hours over two days, in harbor calm and ocean chop, revving from idle to to WOT. I could not make the transmission complain, even with a rapid advance of throttle. And believe me, I tried.

I now believe that the grinding/squealing sound was related not to the transmission, but to the raw water pump.

The pump had worn out was was spraying oily water. The shaft bearing or seal was shot.

I replaced it last week with a new Oberdorfer.

I now assess that the old Sherwood pump shaft, with a worn-out bearing surface, was making the "slipping transmission" noise at certain engine RPMs. And of course the noises stopped instantly with reduced throttle.

Further, judging by reports on forums, most failing transmissions seem to not go in gear, or to be hard to shift. There are some reports of warning noises, but relatively few.

I suppose the lesson is to go slow with any diagnosis that includes ambiguity or mysterious aspects, especially of expensive gear.
 
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