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Old 08-04-2020, 17:13   #1
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Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERSE

Hoping the title will catch the eye of someone with experience with these cone type transmissions. I have a 1GM, it operated fine for years and then slowly developed this issue. It will not go into gear unless revved over 1K at which time it slams into gear with a big clunk. This is true in both forward and reverse.

This issue started slowly and progressed from a clunk that got worse into needing a slight rev to clunk into gear but I was cruising and didn't have the tools to work on it so I just tried to use it as little as possible and figured I would fix it when I got home. Not ideal, I know but I'm due for a repower soon anyway.

It is not a cable issue - this also happens when manually shifting with cable removed. Shifter feels like it moves and engages smoothly.

Once in gear I can throttle back with no issues, the problem is when going from neutral into gear.

Trans oil is a dark amber but smells fine and doesn't appear burnt. It does seem to be overfilled but it is it has been like that since before the issue started.

(Side note, can anyone tell me whether the dipstick is read by resting it on the end of the threads or threading it completely into the housing?)

It happens in both fwd and reverse which has me confused. The service manual has instructions for making slight adjustments to the shift mechanism by loosening the case bolts and moving it either forward or backwards to correct for incorrect engagement of the cone in one direction or the other but says nothing about when the issue is in both directions. It seems to me that if it was wear on the drive cone it's unlikely to be nearly identical symptoms in both forward and reverse.

I'm going to start by draining and refilling the trans but not very optimistic.

I have great access to the shift mechanism on the side of the trans housing but pulling the trans completely is going to be a miserable job, hoping I might have some luck working on it in place.

A couple questions:

-To my untrained eye it looks like the manual says that the drive cone is actually engaged by spring pressure on the 'notch' as it lands on a taper cut into the body of the shifter - ie the shift lever takes you part of the way to engaging the drive cone and then there is a spring exerting pressure on a tapered pin which clicks into place in the shifter and finishes the rotation that engages the cone. Is it possible that my issue is worn out 'notch springs'?

-The manual gives a procedure for lateral adjustment of the shift mechanism (to correct an error where it doesn't fully engage either forward or reverse, which I suspect isn't the issue anyway) using a SST 'locating jig' which basically tells you whether the shift lever is moving through the correct arc. I don't need this tool do I? Seems like the important thing is just that the movement from neutral to forward is the same distance as neutral to reverse so I could take my own measurements without the tool, right?
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Old 08-04-2020, 18:26   #2
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Dark Amber is done on the fluid. Should be threads resting, but a small difference.

If it's not slipping under load, it is a strange situation. do you have a folding prop? Not sure what a cone clutch would slam like that.
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Old 08-04-2020, 18:44   #3
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Quote:
Originally Posted by Boatguy30 View Post
Dark Amber is done on the fluid. Should be threads resting, but a small difference.

If it's not slipping under load, it is a strange situation. do you have a folding prop? Not sure what a cone clutch would slam like that.
Wouldn't say it's dark but it is amber. Definitely due for replacement. No folding prop. I think it's slamming because it's engaging at high revs it just wont engage before I rev it. Oh and I forgot one important part which is that it makes an awful intermittent ka-chunk ka-chunk until it does slam into gear, similar but somewhat different to the sound when you engage a starter while an engine is already running.

Could it be something to do with the damper plate? That's one element of the engine/transmission I don't really understand the function of.
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Old 08-04-2020, 19:00   #4
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

A very familiar tale - glazing of the cones and consequent slipping and clunking is a normal indication of the need for TLC in the lifecycle of these Kanzaki transmissions. I've done mine a few times.

Sorry for your upcoming misery, but you will have to remove the transmission and open it up. The deglazing process is quite easy: search and ye shall find on the interweb, or pm me if you like for more info.

Don't be freaked, they are very simple inside. The worst part of the job almost certainly will be undoing the corroded bolts on the coupling, and that fix transmission to the engine.

What is strange is that it should happen in both forward and reverse - normally it's forward only. The oil should be SAE30, the same as you use in the engine. Amber sounds suspicious and might be a clue to the cause, and to it happening in both fwd and rev. Maybe someone used ATF?

The working force to engage the cones is provided by splines on the shaft inside the transmission which utilise the operating torque to force the cones together (hence the clunk when it finally grabs). The little notch is just to give you some "feel" in the lever operation.

Good luck, and if it's any consolation, you are not alone, and I am happy to help.

Cheers, Graeme
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Old 08-04-2020, 19:21   #5
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Thanks! I think that clears
Quote:
Originally Posted by lockie View Post
A very familiar tale - glazing of the cones and consequent slipping and clunking is a normal indication of the need for TLC in the lifecycle of these Kanzaki transmissions. I've done mine a few times.

Sorry for your upcoming misery, but you will have to remove the transmission and open it up. The deglazing process is quite easy: search and ye shall find on the interweb, or pm me if you like for more info.

Don't be freaked, they are very simple inside. The worst part of the job almost certainly will be undoing the corroded bolts on the coupling, and that fix transmission to the engine.

What is strange is that it should happen in both forward and reverse - normally it's forward only. The oil should be SAE30, the same as you use in the engine. Amber sounds suspicious and might be a clue to the cause, and to it happening in both fwd and rev. Maybe someone used ATF?

The working force to engage the cones is provided by splines on the shaft inside the transmission which utilise the operating torque to force the cones together (hence the clunk when it finally grabs). The little notch is just to give you some "feel" in the lever operation.

Good luck, and if it's any consolation, you are not alone, and I am happy to help.

Cheers, Graeme

Thanks! That makes sense. I didn't catch the bit about the splines using engine torque to engage the cones, I guess that would explain the awful ka-ka-ka-ka-chunk where it's slipping and grinding on the splines until it finally slams into place.
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Old 09-04-2020, 00:20   #6
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Mine started doing what you describe when going into forward. On disassembly I found that the forward gear thrust washer had a slight groove worn into it where it bears on the bellview spring. I reversed the thrust washer and reassembled the box and never experienced the problem again.
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Old 09-04-2020, 01:23   #7
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

First check the stopper bolt length on the shifting mechanism, it is important. If you donít have the instructions in your service manual Iíll post a screen shot of the pages.
The other thing to check before contemplating an overhaul is the rear flange nut. If itís loose then the endfloat on the mainshaft will increase to the point where the cone wonít engage at all. The nut can work loose if the alignment is poor or if there is a shaft vibration.
Cheers, Pete.
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Old 09-04-2020, 06:28   #8
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Also the nut on the shaft coupling is left hand thread. The plate you refered to is bolted to the flywheel And also sometimes refered to as a drive plate. The springs that absorb can break so probably not a bad thing to replace when you have the trans out.

Good thread, I have not experienced the klunking mentioned. The one I had apart had bad bearings due to bad alignment.
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Old 09-04-2020, 08:19   #9
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Quote:
Originally Posted by RaymondR View Post
Mine started doing what you describe when going into forward. On disassembly I found that the forward gear thrust washer had a slight groove worn into it where it bears on the bellview spring. I reversed the thrust washer and reassembled the box and never experienced the problem again.
Thanks. I have what I believe is the FSM but my exploded diagram doesn't have any thrust washers (or anything that looks like a thrust washer to me) or a bellview spring. Will try to attach a picture.
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Old 09-04-2020, 08:21   #10
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Quote:
Originally Posted by skipperpete View Post
First check the stopper bolt length on the shifting mechanism, it is important. If you donít have the instructions in your service manual Iíll post a screen shot of the pages.
The other thing to check before contemplating an overhaul is the rear flange nut. If itís loose then the endfloat on the mainshaft will increase to the point where the cone wonít engage at all. The nut can work loose if the alignment is poor or if there is a shaft vibration.
Cheers, Pete.
I'm also not seeing anything on the shifting mechanism labeled stopper bolt, a section on checking it's length. Would appreciate that screenshot, maybe there is a better service manual out there than what I'm using. Rear flange nut doesn't look like it has shifted.
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Old 09-04-2020, 08:25   #11
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

This is the exploded diagram in my service manual
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Old 09-04-2020, 09:11   #12
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Ah, nevermind. I found a more detailed section which has both the stopper bolt information and shows some 'thrust collars' in the diagram which sure sounds like a thrust washer to me.
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Old 09-04-2020, 09:46   #13
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Parentese.I would like to know how you stop the engine? Since I have nothing on a similar SB8.Thanks!
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Old 09-04-2020, 10:54   #14
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

Hi Calderp , I fight a lot with the same problem and finally Together with an specialist we dissemble all the system only to discover that it's fine looks excellent and the strong noise to connect in both directions I mainly due to be a mechanic engage system and this type of box connect the cone mechanically at major speed than neutral .Part of the problem was solve loosing a little bit the cables who move the connection shift .
Don't worry about the oil because I changed for SAE 30 and then returned to ATF with no noise reduction .At low speed remain a train sound but it disappear a higher rpm like 1000 and with time to be warmer .Maximun reached was 60-70 C degrees.
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Old 09-04-2020, 11:04   #15
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Re: Yanmar 1GM (cone-type trans) needs revving to CLUNK into gear both FWD and REVERS

I'd be inclined to drain the old oil out of it, flush it with kerosene or some such and refill with fresh oil. You might avoid all that dismantling stuff.
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