Hurth Transmission Woes

My Hurth HBW50 slips in forward gear, as I have described on other threads in the past. I am taking a long time getting it done, but planned to pull the trans & replace with the next bigger ZF10. I have the boat mostly apart to pull the trans, but a dockside friend with a powerboat (he crews on sailboats too, so not a bad guy!), says to try this: drain fluid from trans & replace with diesel fuel, run it under a load, but not for too long, then drain & repeat the process. This washes the gunk out. Then a final drain & refill with ATF & smooth shifting & operation may be restored by clutches engaging properly with the gunk removed.

It sounds plausible. I would have to spend another day putting what I took apart back together, test again for slippage, but it sounds like it may be worth it.....it would certainly be worth it to save the cost of a new trans (>$1000).

Has anyone ever tried this or heard of it working before? Any transmission gurus who can chime in on this??? Cap'n Bill??

P.S. The Hurth trans uses internal clutches, one for forward & another for reverse.

I have heard that flushing a car's automatic transmission by either a commercial method or by multiple fluid changes may help prolong the life of a failing transmission. But I would think this is only a temporary fix. If the clutches are slipping because they are worn it doesn't seem like it would make a lot of difference. If they are slipping because the wrong type of fluid was used, or something else got in there, maybe it would work.

I have never taken a Hurth apart however....

Since it is a mechanical transmission, that is, AFAIK, it doesn't use hydraulic pressure to engage the clutches like an automatic transmission in a car or boat does. So flushing it with fluid is likely not going to do anything. The reason it works in hydraulic actuated transmissions is it is flushing out the piston and seal areas that do get crudded up. I am guessing that Hurths use a cone type clutch and when they go, there gone. Even if it did work its on borrowed time.

RT

rwthomas1 said:

I have never taken a Hurth apart however....

I am guessing that Hurths use a cone type clutch and when they go, there gone. Even if it did work its on borrowed time.

RT

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Rob & Mherrcat,

Nigel Calder's Boatowner's Mechanical & Electrical Manual, 3rd Ed., has an excellent section on trannys, including cutaways of the Hurths. To quote, "In manual two shaft transmissions, when the clutch engaging mechanism is first moved..., it gently presses on the relevant clutch. This initial friction spins a disc carrier, which holds some steel balls in tapered grooves. Because of the taper in the grooves, the balls exert an increasing pressure on the clutch, completing the engagement."

So, yeah, it sounds like he is describing a "cone type clutch." Perhaps "steel balls in tapered grooves" could be impeded by 25 years of built up crud. This problem might have been coming on for a while, too, leading to clutch slippage for an extended period. Hmmmm, decisions, decisions!

transmission flush

I try this method and did not work for me ,when the transmission start to loose grip on disks cluth that mean there is too much wear ,so the cluth is no longer able to put enough pression on the disk. IF you want to rebuilt your transmission by your self you have to change not only the cluth disks but the cone mechanism too, because that is the cause of failure combine with the disks cluth. I try to change only the disks cluth in order to save money and the transmission failed again one year later . If you change disk and cone parts you gone pay as much as a rebuilt transmission. I put a brand new hbw 50 and the trans.failed three year later , I just put the new zf 10 and that transmission look more robust and able to make the job right, the hbw 50 is too weak and push close to is limits all the time and can not be reliable if you go over 1800 RPM
Éric
Decision
Ericson 35 mk3

more Hurth info

Everyone,
I routed this thread over to a professional diesel mechanic friend and he responded and gave permission to add his comments here:

"Having rebuilt a number of Hurth transmission during my career, I've found two things, Shift cable or shift lever out of adjustment not allowing the pressure plate /roller ramp mechanism to function properly, or have found some gear boxes not set up correctly at the factory with the right amount of shims to properly space the the pressure plate /roller ramp mechanism to the clutch discs not allowing full compression engagement of the friction discs.
I question the validity of flushing to correct a slipping problem unless somebody installed some super slick substance like STP."

What are the symptoms of a transmission slipping? Is it a variation in the engine RPM? Just curious in case I happen to encounter it with mine...

Can you say, "fend off?"

mherrcat said:

What are the symptoms of a transmission slipping? Is it a variation in the engine RPM? Just curious in case I happen to encounter it with mine...

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Thanks, everybody for the great, thoughtful responses!

Symptoms include:
1. Backing out of slip, everything is great. As the boat slows, move the shifter to forward & apply throttle.....nothing happens (except the boat drifting toward other, very expensive vessels). Repeat the process 2 or more times and maybe a very soft "clunk" is heard, whereupon forward motion begins.
2. Some loss of speed through the water.
3. Bought a cheap (~$25) laser optical tach on Ebay. Measured the RPMs of the crank pulley vs. the prop shaft (expecting a 2:1 ratio). Found the ratio actually varied (dropped) as more RPMs were applied to the engine under load. Prop speed dropped as engine speed increased.

All this was after replacing the shifter cable, shifting the trans by hand, reaching down from the quarterberth, to try to get engagement in forward gear (as the admiral tried to steer our disabled boat & warned others out of our way!). This whole fiasco has not won me any points (except the bad kind:hoppingmad:)

Tranny R & R

Moving forward with trans R&R, I lifted the aft end of the engine using a combination of a come-along attached to a 4X8 beam across the companionway and a scissors jack beneath. I unbolted motor mounts, removed all the bolts from the circumference of the bell housing. I then tried to pull the bell housing and trans assembly back off of the pilot shaft, but no success. I tried to pry with large screwdrivers, but still no luck. There is not really anyplace where you can insert a screwdriver tip to pry the bell housing away from the engine flange. Can anyone give me any tips on separating the bell housing from the engine? The starter bolts don't pass through the engine flange and thread into the bell housing, do they?

Thanks for any advice you can give!

P.S. I didn't mention it on this thread, but it is a Universal M25 and I'm doing this with the boat in the water.

Keith,
You are probably done with this job by now, but with the motor mounts free and ALL the bolts (some are bolts and a few are bolts with nuts) around the circumference of the bell housing removed the housing and the tranny should easily slide aft. All that is left holding is the friction of a couple alignment pins AND the shaft spline of the tranny into the flywheel adapter. My M25 easily came apart (twice-once to rebuild and again to install a new ZF10) . And no, the starter bolts do not screw into the bell housing. Also, sorry, I don't know where to pry to free the housing.
Also the "professional diesel mechanic" mentioned above in Loren Beachs post is right on the money. I rebuilt my old Hurth and shimmed the clutch stack wrong and it failed in about 50 hours. Our local diesel shop said they don't rebuild these small Hurths but sell parts to those of us who choose to - a bad decision for me. I now have a new one!
Let us know how it goes.

Jerry,

Yes, the removal job (at least) is done. I had taken all the bolts (including those with nuts on the back) that were around the circumference of the bellhousing off....or so I thought. There was one bolt from the front (opposite of all the rest), through the engine flange, threaded into the bellhousing that I didn't see with the poor access. Finally the sharp eyed admiral spotted it. Here's to her! She cranked the ratchet wrench to remove that bolt and the tranny & bellhousing practically fell out in my hands.

The new trans & damper plate are ordered. I hope engine & propshaft alignment is not too difficult. When you switched to the slightly longer ZF10, did you have to move or re-orient the engine much? I'm thinking that as the propshaft has to move back, it will drop lower & necessitate lowering the aft end of the engine a bit. We will see.

We can't wait to get sailing again. It has been a long time.

Thanks again to all for the assistance.

Keith,
A PO had changed my tranny from a ZF5 to a ZF10 before me. All they did was slide the prop shaft aft to compensate for the longer tranny. Shaft alignment was not an issue that way. But, not the best as solution because the prop now hangs further aft too (now about 4 1/2 inches behind strut) and it does not allow room to install a dripless packing or flexible shaft coupling either. But, it all works well as is. Good luck. There is lots of good info on aligning the shaft to compensate for shaft weight hang etc. Are your motor mounts in good shape? Good time to swap if not.

Completion

I wanted to let the group know that I finally completed this arduous task of trans replacement (HBW50 to ZF10). Trans installation was not too bad once I had learned the hard lessons from removal. Re-alignment was required. If you draw yourself a little diagram of the engine, trans and propshaft from the side (don't forget that the trans output is lower than the input....not on line with the engine crankshaft), you can see that by elongating the trans, which is what I did by changing to a larger unit, you change the relationship of the engine/trans unit to the propshaft. I had to raise the nose of the engine, drop the tail a bit, to achieve alignment. It is funny to me now that it is often referred to as " prop shaft alignment." The prop shaft is the fixed portion of the system. Only the length of the propshaft can be varied in the system as it exists. It is actually the engine/trans that you move into alignment with the fixed in position propshaft. I had to get this straight (pun intended) in my head before I could get it straight in the boat!

First sail was July 5th, our Independence Day!

Excellent!

Keith Parcells said:

...First sail was July 5th, our Independence Day!

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Cool!

Congrats on finishing the job - and enjoy the remainder of the season, as there is still much of it to go!

//sse

And now, a Leak

I was going to start a new transmission thread around my problem... which is a just-discovered oil leak. Upon some thought, this is just another "woe."
Basics: Engine is a 1988 23 hp Universal M25XP. 1863 hours on it.
It is not a major leak, yet.... but appears to be coming from somewhere in the area of the shifter (starboard side of the case). It is really difficult to get a clear look at it. There is only about 10 fl. oz of ATF in this tranmission. Any sort of significant leak would quickly destroy the trans.

Loss seems to be a few drops of red atf after 3 hours run time @ 2500 rpm, last weekend.

Prelude: I just added about an oz to the trans after finding some loose atf oil under the engine this spring when cleaning everything up... So it could have leaked out last fall, for all I know. The atf was under the drip pad beneath the engine and not visible until I removed the pad to replace it as part of the spring oil and filter change.
So, what to do?

Anyone have any experience with a leaking Hurth (probably a model 50) of this vintage?? I have done some on-line research and find that Hurth is nowadays ZF. This model is long out of production. The new replacement would be either a ZF6M or the longer and stronger ZF10M. If replacing, the length of the new ones is about an inch more than the original model 50, per one web site table I found. Moving the engine mounts forward is do-able but not desirable, or I could probably shorten the shaft an inch which requires a haul out.

Biggest hassle would be moving the engine forward about six feet into the cabin to get at the bell housing and trans. That's about 270# of recalcitrant diesel that would be really hard to get a grip on, being under the bridge deck.

Plan B is just to live with it and hope it does not get worse... However, in order to get to the broad waters and spacious sailing of Puget Sound and the delights of the Ericson Rendezvous, we have to be able to motor hard, north, against prevailing wind and off shore currents, for at least 28 straight hours. This is not optional. Summer conditions can often be 7 footers at 10 seconds... Slamming into it and hanging on is required and sometimes one's inner ear coping can be tested a bit.
I have done this at least 20 times in almost as many different boats over the years. Some trips were on flat water, most were not.

If staying in the Columbia River estuary for the summer cruising season or even sortieing up to Grays Harbor for a nice ocean day trip, one can stretch one's maint. $$ a bit further, any keep one's towing insurance paid up.
Doing the Full Monty, for us Portland sailors, like a bash up the length of Washington coast to the Juan De Fuca Straits or better yet to Barkley Sound, calls for 100% faith in the drive train of any boat, sail or power.

So, based on limited information, there are suddenly some summer cruising decisions to make.
Least of which is to try and decide if it's better to spend several thousand $ on labor and parts on the trans. or just to drop in a new engine/trans for 7K.

Anyone with some Hurth-related thoughts on leaks, seals, and related prognostications may chime in at this point -- Please!
Thanks!!
:nerd:

Regards,
Loren

Ouch, that sucks. Didn't someone here swap a trans with the boat in the water? I seem to recall pics of an engine pulled/flipped forward into the salon..... Simply replacing with a rebuilt unit may be the easiest option. Unless the diesel has been poorly maintained the hours on it are certainly not enough to warrant replacing it. I'd look hard into finding a rebuilt unit, keep a close eye on the leak, get all the bits together and then have a "trans swap party" Don't we all have buddy's who like to turn wrenches for fun? RT

Yup. BTDT. That was me Rob. Bringing the boat home from MA after buying it. Lost the tranny and drifted into a mooring in Marblehead. Bought the new tranny Sat morning and swapped it that day. Motored home to Portland Sunday. See the link.

http://treilley.myphotoalbum.com/view_album.php?set_albumName=album23

Hey Tim, Where did you ever find another Hurth 50 for sale? And, how was the condition of the old torque springs in that damper plate when you got access to it?

Loren

They were still being sold at the time(2006). Hansen Marine is less than a mile from the waterfront so we walked up first thing in the morning and bought a new tranny while a buddy of mine drove south from Maine with his tools. We got a ride back to the launch by one of those fellow sailor types and disconnected everything to prep for the lift when my buddy arrived.

I did not even look at the damper plate because I decided it was a good idea to replace that too. I used to work on cars a lot and there are certain things you always do when replacing certain components. When you replace a timing belt, do the waterpump, seals and accessory belts. When replacing a tranny, replace the clutch too.

I still have the old tranny with bad forward gear. I have been meaning to rebuild it so I have a spare but I am too busy with other projects.

Loren,

I replaced the HBW 50 with a ZF10m on my 911 se this winter. The HBW 50s are woefully undersized for anything less than 15 hp and do not withstand the rigors of extended motoring. The ZF6 is smaller than the ZF10. However, for the nominal difference in cost it make little sense to use the ZF6, as is neglecting to replace the damper plate during the process.
Before you relocate the engine mounts, check to see that you already have the clearence at the back. The 911 se has a small partial bulkhead aft of the transmission. In my case, no modifications were necessary. But this could have easily been cut down w/o comprimise to structrual integrity.
For the conditions you describe, I wouldn't chance it, as you will have to replace this soon anyway.
This is my second transmission in 8 years. The first was a rebuilt HBW50. My frugality got the best of me on this one.
BTW thanks for the keel bolt torque info.

Ed.