125SX clutch issue

Matt Fisher
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1/27/2021 6:12pm
So I upgraded the clutch on my 17 125SX to a full Hinson, and since then have not been able to get it to fully disengage. Completely pulling in the clutch results in the bike creeping forward, or stalling if no throttle is used. When I pull the cover off and look at the pressure plate, it does not move anywhere near as far away from the friction plate as the YZ250, CR250 and YZ85 that I have recently looked at.

Thinking I needed to rebuild the master and slave, I did so using All Balls kits. Very slight improvement- maybe.

I have used an entire quart of DOT 4 fluid bleeding the dang thing. Vacuum bled it with a rather handy Harbor Freight air tool, reverse bled it with a large syringe, and have even used the syringe to push fluid in, then pump it back out with the lever, all while looking for bubbles. I've removed the slave and hand pumped it back and forth to the master. No scoring on the slave cylinder, and although I can't see down the master, I've cleaned it with brake cleaner and several Q-tips.

I re-installed the entire factory clutch, and the pressure plate still doesn't move much off the last friction. Pumping the clutch lever has no effect on how well it works. I zip-tied the clutch lever to the bar overnight, and in the morning, it still felt the same as the night before.

I also was able to feel the clutch on a 21 125SX and felt much better to my hand. Immediate "firmness" in the lever, made mine feel a bit mushy in comparison.

Before I plunk down the cash for a new master and slave, any suggestions?
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FWYT
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1/28/2021 8:21am Edited Date/Time 1/28/2021 8:23am
I know I've struggled to get my KTM 200 clutch bled properly a few times. Before you buy anything else, try loosening the slave from the cases before you bleed it. As in back off those three bolts several turns so it is still attached, but there is a several millimeter gap. Then bleed, then tighten back down. See if that helps.

Also, and I don't know that it will affect this particular problem, but I thought brake fluid was not recommended in those clutches? (I think I used fork oil last time I did mine.)

Let us know what happens. Good luck!
Rickyisms
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1/28/2021 11:02pm
FWYT wrote:
I know I've struggled to get my KTM 200 clutch bled properly a few times. Before you buy anything else, try loosening the slave from the...
I know I've struggled to get my KTM 200 clutch bled properly a few times. Before you buy anything else, try loosening the slave from the cases before you bleed it. As in back off those three bolts several turns so it is still attached, but there is a several millimeter gap. Then bleed, then tighten back down. See if that helps.

Also, and I don't know that it will affect this particular problem, but I thought brake fluid was not recommended in those clutches? (I think I used fork oil last time I did mine.)

Let us know what happens. Good luck!
The newer ones take DOT 4
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Rickyisms
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1/28/2021 11:04pm
How does the bore look where the piston goes in? Any knicks or scratches?
FWYT
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1/29/2021 8:04am
Rickyisms wrote:
The newer ones take DOT 4
Thank you! Good to know.

The Shop

soggy
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1/29/2021 9:17am
I’d be suspect of the all balls rebuild kit first off, I have not be impressed with the quality of there seals or bearings.
Matt Fisher
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1/29/2021 9:26am
Rickyisms wrote:
How does the bore look where the piston goes in? Any knicks or scratches?
Not a mark on it. Looks great.

FWYT- I tried that, and also tried completely removing the slave and alternating pushing the piston in by hand, pumping the lever, drawing fluid in with the syringe and then pushing it back with the syringe.

If the lever didn't work at all I'd have to conclude that the master or slave was bad, but that's not the case.
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FWYT
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1/29/2021 1:47pm
Man, strange . . . happening with both clutch packs . . . any chance that thrust washer that goes between the basket and hub could be contributing some drag somehow?
CarlinoJoeVideo
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1/29/2021 4:30pm
I've replaced the rod that goes from the slave to the clutch and that helped.

Your plates are installed the right way?

They are a pain to bleed so don't beat yourself up about that part.
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Matt Fisher
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1/30/2021 5:03pm
I've replaced the rod that goes from the slave to the clutch and that helped. Your plates are installed the right way? They are a pain...
I've replaced the rod that goes from the slave to the clutch and that helped.

Your plates are installed the right way?

They are a pain to bleed so don't beat yourself up about that part.
Plates start with a friction, go to a steel with the sharp edge out, then alternate and finish with a friction.

FWYT- my friend had an issue with over-tightening a hub on a 450 Katoom causing drag, so I was careful to make sure it spun freely before adding the plates.

soggy- you may well be right, though I would think if the seals/o-rings were bad then no pressure would be developed.



So I decided to try an experiment- I hooked up a Yamaha brake master cylinder (11mm vs the 9mm on the clutch) to see if maybe I could isolate the issue. After bleeding it, I discovered that it does indeed move the pressure place out much further than the KTM clutch master does. The question is if that was only due to the larger piston moving more fluid.

I pulled the master apart and using a flashlight carefully looked over the bore. Not a nick or scratch in it. Next I took a small roll of 1000 grit sandpaper and carefully turned it inside the bore- in and out etc. Cleaned it up with brake cleaner, let it dry and re-assembled. Power bled it with the vacuum device, then pressure bled it with the syringe. Lastly I loosened the bolts a bit and pressure bled it a bit more. Zero change, the pressure plate still doesn't hardly move.

Pretty sure that come Monday I'm going to order all new KTM parts. This is infuriating.
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Hcallz5
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1/30/2021 7:39pm
I rebuilt my clutch slave with an aftermarket rebuilt kit and it wouldn't work right, I had to order the OEM plunger thingy to get it right.
Matt Fisher
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1/30/2021 8:15pm
Hcallz5 wrote:
I rebuilt my clutch slave with an aftermarket rebuilt kit and it wouldn't work right, I had to order the OEM plunger thingy to get it...
I rebuilt my clutch slave with an aftermarket rebuilt kit and it wouldn't work right, I had to order the OEM plunger thingy to get it right.
Unfortunately, the piston is only available from KTM with the new slave cylinder. They're really proud of the plastic piston in the master, it retails for $60!

I'm thinking that once I have the new parts, I can figure out what is actually wrong, fix it, and then sell the old stuff and make back a portion of my money. Of course, I could be mistaken about that too...
FWYT
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1/31/2021 8:39am
Oh man, drag! I feel your frustration. Hope you figure it out. Let us know what happens.
Paw Paw 271
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2/2/2021 6:16am
FYI... Different trans oils will change the drag in the clutch.

Paw Paw
Matt Fisher
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2/2/2021 8:47pm
FYI... Different trans oils will change the drag in the clutch.

Paw Paw
Agreed. I've tried both Redline Shockproof Lightweight gear oil and some off the shelf 5W40. No change.


I ordered a new master, slave, crush washers, pushrod, and throw-out bearing. So the only thing I'm not replacing is the line. My plan is to install the items one at a time, bleed it, and figure out what caused the problem. I'll post my results.
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