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Old 15-06-2017, 08:49   #1
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ZF10M transmission explosive shifting.

Anyone knows of this or can recommend an expert? I have bought used ZF10M from a fisherman in Alaska, with some verbal assurance that it was OK, but no guarantee. Took a calculated chance. Figured that worst case, I will rebuild it. The original was Hurth HBW50 (on a '82 Universal M25 diesel) and it lately suffered from the here oft debated problem of not going into forward. Now, half year later, the 1" longer ZF10M is finally installed and it goes in forward and reverse, but it does so with what seems like unnecessary gusto. The klonk is very loud and to my mechanic's ear it sounds like it won't be long before something breaks.
I have installed new damper plate, the idle is low, where it's supposed to be and there is a PIY flex coupler. On the bench, it seemed to turn smoothly, no play in either shaft, but a little too tight for a well used transmission, as if the bearings were in some pre-load. The previous transmission, from brand new, made much more reasonable klonk when engaged. (Of late, no klonk at all)
I wonder if someone has rebuilt the transmission and did not adjust some clearances properly. I have, 23 years ago (it worked well until few years back) rebuilt the Hurth because of water intrusion and remember the shims, the calculations and the mysterious clutch engagement assemblies. Could the type of ATF used make a difference? (Now I am clutching at straws).
Any ideas? Thanks Stan
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Old 15-06-2017, 15:19   #2
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Re: ZF10M transmission explosive shifting.

A well written summary of the issue. Someone will have good advice. Sorry I don't.

But on the off chance,.... do you know that your keyway on the propshaft and the key are in good shape? Ive seen one run loose and beat up the keyway. It will add to the clunk sound rather dramatically.
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Old 30-04-2018, 18:04   #3
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Re: ZF10M transmission explosive shifting.

ZF10M transmission explosive shifting.

I am re-posting my question from 10 months ago, with some further notes. Except for some sympathy, there was not much in the replies.

Anyone knows of this or can recommend an expert? I have bought used ZF10M from a fisherman in Alaska, with some verbal assurance that it was OK, but no guarantee. Took a calculated chance. Figured that worst case, I will rebuild it. The original was Hurth HBW50 (on a '82 Universal M25 diesel) and it lately suffered from the here oft debated problem of not going into forward. Now, half year later, the 1" longer ZF10M is finally installed and it goes in forward and reverse, but it does so with what seems like unnecessary gusto. The klonk is very loud and to my mechanic's ear it sounds like it won't be long before something breaks.
I have installed new damper plate, the idle is low, where it's supposed to be and there is a PIY flex coupler. On the bench, it seemed to turn smoothly, no play in either shaft, but a little too tight for a well used transmission, as if the bearings were in some pre-load. The previous transmission, from brand new, made much more reasonable klonk when engaged. (Of late, no klonk at all)
I wonder if someone has rebuilt the transmission and did not adjust some clearances properly. I have, 23 years ago (it worked well until few years back) rebuilt the Hurth because of water intrusion and remember the shims, the calculations and the mysterious clutch engagement assemblies. Could the type of ATF used make a difference? (Now I am clutching at straws).
Any ideas? Thanks, Stan.

PS I forgot to bring up work I have done on a boat with a larger Hurth gearbox (on Perkins 4-108) where the shaft actually came out of the flange after destroying itself, the key and the flange. The owner did not mention and problems with the transmission, but when we installed new shaft, flange, damper plate and flexible coupler, the gearbox shifted with similar loud clonk. The idle RPM was rather high and after fixing a sticky linkage and lowering the idle, the clonk became tolerable to my ear.
Since then, I observed another ZF-10 transmission with a loud shifting. Can it be the nature of the beast? Again, my old Hurth 50 worked well for thirty years, twenty after a rebuild, with a sound about like when you shift a motorcycle into first gear.
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Old 30-04-2018, 18:49   #4
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Re: ZF10M transmission explosive shifting.

I just had my ZF 10 rebuilt after 30 years of good service by an older guy who is supposedly the best for these transmissions in Miami but now I get a loud clunk when shifting! I now shift very slowly and at idle rpm only. The old trans was quiet shifting but starting slipping. It was expensive getting the trans out, parts, rebuild cost, and reinstalling the trans. Now I hope it will be ok! A new ZF would not align due to change in elevation of output shaft. The joys of an older boat!!!
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Old 30-04-2018, 18:55   #5
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Re: ZF10M transmission explosive shifting.

Is it possible you have the wrong damper plate? Springs a bit too weak for the new trans?
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Old 30-04-2018, 18:57   #6
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Re: ZF10M transmission explosive shifting.

Thanks Dneve, I would have bought a new one, but they were all sold out and they don't make them any more. I am asking my question about it precisely because I'd hate to take it out and rebuild it and end up right where I started. Hopefully someone will shed some light on the subject.
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Old 30-04-2018, 19:15   #7
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Re: ZF10M transmission explosive shifting.

thanks PCMM, considered that, or more along the lines of having defective new damper plate. I did research the replacement carefully, and though the new plate is different manufacturer and part number, it was supposed to be correct replacement.
The thing is, it makes the horrible clonk even when with the flex coupler is removed, shaft disconnected. That must make big difference in the demands on the damper plate.
Another clue that tells me nothing. In the last year of the failing Hurth 50, there was no clonk at all as the transmission failed to engage in forward completely, but persistence always paid off, eventually, sometimes after twenty tries, the tired transmission did engage normally and worked without slipping for hours and hours. It seemed that once it warmed up, it would shift in forward much more readily, sometimes reliably. BUT. Once in a while, it would engage with the same horrible clonk as my new (to me) one does.
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