Hurth Tranny Bad Reverse

[waterman46]

Lately the Hurth HBW20 transmission on our boat sometimes does not shift into reverse. The problem is intermittent, so most of the time it will shift perfectly but seems to fail the shift about 1/4 of the time. Single lever Morse linkage checked and looks fine, nothing loose I can detect. With engine stopped, removing cable connection at the tranny I can operate the shift lever by hand and feel and hear the click as I move the lever to forward, neutral and reverse. Bolt securing lever to shift rod is tight.

Fluid is at proer levels in tranny.

Can this behavior be caused by some internal wear in the tranny or must there be something in the likage I missed?
.

[Dennis.G]

If it really is not shifting into reverse most likely the single lever control unit or linkage adjustment. Sounds like you have examined that however.
Another possibility is that the transmission is shifting but is slipping badly. This could be due to worn clutch plates on the reverse section. There would likely be some prop rotation, but bad slippage when adding power. If transmission were stressed (caught up in crab pot lines etc) the clutch plates could have been burnt. If this is case, can be rebuilt with new fiber clutch plates. Would note that clutch plates usually fail in forward gear however. Check tranny fluid for bad color, smell, or excess fiber or metallic content. Change fluid anyway.

[waterman46]

I drained the oil - it seems a bit dark but does not have the burnt odor I have experienced before the latest rebuild. No metal could be detected, but guess I should have used a magnet in the oil. I just refilled it with the same oil, since I have a limited supply on board right now. Tomorrow I will again disconnect the cable at the tranny and with the engine running this time, I will see how the shift lever operation feels and works.

We did run across some kelp and perhaps one lobster pot on our trip down to Puerto Vallarta from San Francisco. I remember a couple times we had to go to reverse gear to clear something on the prop.

[Suijin]

Originally Posted by waterman46

...but does not have the burnt odor I have experienced before the latest rebuild..

The transmission was rebuilt? By who and how long ago?

[TCL]

I don't want to hijack your thread, but I'm very interested in the responses here. I just installed a brand-new ZF Hurth 25 and new control cables, and on the maiden trip back from boatyard to marina, the transmission stopped shifting into reverse. It would stay in neutral, then when the throttle got high, slam into reverse gear. Once I safely got into the slip, I undid the cable linkage at the transmission housing, same as waterman46, and could shift the lever by hand without problem. Transmission fluid was fine. I'm going to continue to check the linkages, but will be monitoring these posts for other thoughts. Thanks.

[Uncle G]

If you have the morse cable disconnected and manually 'click' the gearbox into reverse - can you then reconnect the morse cable when the shift lever is in the reverse position?


Maybe there isn't quite enough travel in the cable and 25% of the time it doesn't quite make the 'click'?

[jen1722terry]

MaineSail did a commentary on the newer Hurth/ZF transmissions, along with photos. I forget the name of the clutch part that fails (friction bearing, maybe?) but it causes slippage or non-engagement in forward. Symptom is black trans fluid. Prevention is to change fluid more frequently (we did it every 75 hours but the second trans still failed).

We had two fail (ZF-10 size) on our 31-foot sailboat within a year. ZF arranged for replacements, but it took time out of our short Maine summer. When another issue arose with our old engine, we decided to re-power with a Beta 25.

Hope this helps. The MaineSale tutorials are really helpful on this issue.

Terry

[Mike Banks]

This is a problem with single lever controls. I never liked 'em--even though the one I used until recently only ever gave the same trouble as you mention until I dismantled the whole thing and used lithium white grease on all moving parts.

My gearbox was a Kanzaki--but the linkage things are similar.

The thing is--how long has this been happening? In mine the oil was burned because of the slippage, but I replaced it with automatic transmission fluid and flushed it out before replacing the oil again with the recommended grade and type.

There were no further problems--but perhaps I was just lucky.

[aquafacts]

The problem may be improper adjustment on your cable but also a very likely problem is slippage as the HBW20 is undersized for your 46' boat ! That is a tiny transmission - smallest of Hurth line ! Rather than rebuild again - a direct replacement is a TechnoDrive TMC 40 or 60. Either will bolt directly to your bellhousing but both are slightly longer and the 60 is slightly taller being a much more robust trans. A cooler can be added to the TMC60 model. All are readily available online for great prices compared to Hurth.

[Uncle Bob]

Originally Posted by aquafacts

The problem may be improper adjustment on your cable but also a very likely problem is slippage as the HBW20 is undersized for your 46' boat ! That is a tiny transmission - smallest of Hurth line ! Rather than rebuild again - a direct replacement is a TechnoDrive TMC 40 or 60. Either will bolt directly to your bellhousing but both are slightly longer and the 60 is slightly taller being a much more robust trans. A cooler can be added to the TMC60 model. All are readily available online for great prices compared to Hurth.

Hi, when the hurth in my boat failed I replaced it with a PRM, straight swap although marginally longer. Great gearbox.

[patprice]

Originally Posted by Uncle Bob

Hi, when the hurth in my boat failed I replaced it with a PRM, straight swap although marginally longer. Great gearbox.

Ditto.
I too tossed my ZF10,s too many clutch problems possibly due to cruising in the tropics.
My PRM did require the engine be lifted by 10 mm which was easy.

[junkmanii]

I have experienced similar issues that turned out to be a cable locking problem. The "ubolt" that held the cable stationary in the shift box on the helm station had come loose. Never could figure why it worked one way and not the other. I'd sure check this before replacing the clutch!

[wcapman]

I have a Hurth transmission on a Yanmar 2GM20F. This was the original transmission on the boat originally with a 2GM13. I realize this transmission is not recommended for the larger engine, but after 800 hours it is still working well. I had it rebuilt when I re-powered. The shop that rebuilt it said the reverse cone clutch was burned probably from sailing with the prop freewheeling. They recommended always sailing with the transmission in reverse to lock the prop and prevent freewheeling. I've never heard of that before but after 800 hours there are no apparent issues. Just thought I'd pass that along.

[waterman46]

Thanks to all for the information and suggestions. Right now I don't know if we will try to replace or rebuild the transmission as we would like to continue our cruise without a long delay here in Puerto Vallarta. Today we ran the engine several hours getting here, and tested for reverse gear several times. It worked fine all day, except for once just coming into the slip (of course) but when I returned to neutral on the Morse then slowly tried reverse a second time, it worked.

I have not been able to locate a supplier for a rebuilt HBW20. Maybe we will have to go with one of the suggested alternate units - need to do a lot more research on this. I am quite certain we could fit a different transmission if it wasn't more than one or two inches longer.

This transmission was rebuilt in Dec 2016 in Chula Vista CA, I can't remember the name of the mechanic. We needed the oil seals replaced. I don't think they did anything with the clutch plates as there were no shifting or slippage issues then. Since then we have put about 1200 hours on it.

[Siberian Sea]

Inside the planetary gear housing is a set of forward and reverse clutch friction cones or plates. When your engine is running it’s turning a gear pump located on the input or engine side of the transmission. When not in gear this fluid being pumped will bypass the gear housing. When you shift into gear forward or reverse the rotory valve you cable is controlling will direct the fluid into this housing and the pressure (perhaps around 135 psi) will cause the friction plates or cones to be pushed into contact with the drive cones sandwiched in between. Over time of course they wear and then you transmission will slip a bit or even stop working all together.
I believe your friction plates are telling you it’s now time for an internal rebuild. If you transmission has an external oil cooler like it should have you can take the hose going to or the return hose off and install a simple pressure gauge with some brass T fittings. Best to use a quality oil filled gauge that can go to 180 psi. Now reconnect the hose with your new gauge installed as part of your system.
Start engine and look at gauge and notice the oil pressure. With this cheap add on (parts all from Napa Auto) you can monitor your transmission oil pressure and have a better idea of its health.
Transmissions don’t have filters so do it a favor and change fluid often.