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slave cylinder o ring

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so after a long search for an o-ring that fits around the slave piston i finally found one that seems to work. so i go to change the oil and realize that there is an 0-ring that is exactly the same size around the oil cap. figures! so if anyone is having the same problem as i did with a leaking clutch use that o-ring or order it instead of buying the $100 piston o-ring combo:banghead:

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Check the bore of the slave for wear. Sometimes its not just the o-ring. The piston can get cocked and wears a groove.

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Thanks for posting that and glad you found one that works. The O-rings are not listed. This forum has helped me quit a bit, so just trying to help make your information more useful for others.

Along those lines, what bike do you have? Model, year, etc? Maybe even an O-ring part number if you got one?

Gary

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2000 ktm exc 200

21: O-RING 16,00X3,00 NBR 70

part # 4371401-001

from bikebandit.com

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The o-ring for the counter shaft is the same as the slave, also.There is a listing for those.

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The o-ring for the counter shaft is the same as the slave, also.There is a listing for those.

This is partially true, or could be true depending on how worn your slave cylinder and which bike you are getting the counter shaft seal from.

The counter shaft o-ring from a 200 is 23x2mm which is oversize, but might work with a worn cylinder. The counter shaft o-ring from a big bike (250/300) is 25x2 and too big for any cylinder. If the slave cylinder is worn and or grooved you can sometimes get away with sanding it, smoothing the edges of small grooves and use and oversize o-ring.

Here is a ref. for some parts options you can use to rebuild your slave cylinder.

Clutch Slave Cylinder COVER O-Ring, 30,00X1,50MM ............. KTM P/N 770300015

Clutch Slave Cylinder O-Ring 23.52 X 1.78 mm .......................KTM P/N 770020210

Clutch Slave Cylinder O-Ring 23.52 X 1.78 mm McMaster-car

Clutch Slave Cylinder O-Ring (oversize) 23.00 X 2.00 mm .........KTM P/N 770230020

Clutch Slave Cylinder O-Ring (oversize) 23.00 X 2.00 mm ........ McMaster-car P/N 9263K502

It is in the FAQ's too, including how to do it, but this is expanded a bit as far as P/N's.

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I don't know that one is more dependable then the other.

I think the Magura clutch works pretty well and last a long time. I think most of the problems come from putting dirt in the system from bleeding through a dirty bleed nipple. This could be prevented by running a 5 cent plastic cap from Lowes over it.

I would think the issues with the Brembo clutches would be the same as the Magura's with the addition of the problems brakes have. Brake fluid draws moisture in from the air and that can cause corrosion to pistons and cylinders as well as much things up. You just need to change the fluid occasionally and like you said you really wouldn't want it to leak into the tranny.

On either system after a few years if the o-ring is compressed and taken a set into a square shape this will let the piston rub on the cylinder and cause more wear. Either system kept up with like you are, kept clean, and with an occasional seal replacement may last virtually indefinitely.

Either way the advantage you have is in having an '09 bike. I wouldn't expect any problems with it for awhile. :thumbsup:

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I just changed fluid in mine with 2.5 wt fork oil. After all this talk and direction I was starting to worry mine might be wearing grooves in there.

It was a little dark with something like metal wear particles like dirty motor oil. Some of it had settled on the bottom of the master cylinder and I brushed it out and blotted it up with a paper towel sever times. I also drained some fresh fluid down through the hose.

The o-rings looked good and the slave cylinder bore looked new (no wear marks or grooves). There was no dirt in there because I haven't bled it before and I keep a plastic cap on the bleed nipple. I took the nipple off and cleaned it out anyway.

After reassembly, I back bled with a syringe with no problems, except as I said before it needs a touch of bleed from the top down at the end to get the air out of the top of the slave cylinder and bleed passage after bleeding bottom up (back bleeding). Air is trapped there because you are trying to force it down hill when back bleeding. I got two little bubbles out when down bleeding.

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I think the contaminated oil is suspicious... On my problematic 450 the oil would turn black too, I figured then that it was particles form the slave cylinder shavings or maybe engine oil making its way in the hydraulic system.

Did you take the piston off while inspecting the slave cylinder?

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Yes. I took the slave cylinder piston out, that is how I knew it was perfect with no wear marks, shiny spots or grooves. It shows no signs of wear at all. I didn't take the master cylinder apart.

The oil was reddish (maybe Magura blood) and almost clear with a slight tent of black and some sediment on the bottom of the master cylinder. Enough to see the darker color on the bottom of the reservoir on the metal. You couldn't see the fluid was tented standing in the reservoir. It didn't show until it was on white paper towel.

I didn't see any sediment in the slave cylinder, but there was enough dark color in the fluid, again, to show on the paper towel that I wiped it with to make me want to flush it. I flushed the whole system. I always see some of this in brake systems or any thing with oil and moving parts for that matter. There is no telling how long it has been since this system was opened and how old the oil is. I know it is at least 1 year old and judging from the condition of other things I have rebuilt or replaced it is probably many years old. So, I think that is pretty good and normal. Kind of amazing really.

The more I think about it I think the dark sediment is from the o-rings, piston seals, and or rubber diaphragm in the master cylinder cover. It could be degrading and about to go, but I think it does that for years before giving up, although it probably has been doing that for years.

Anyway, it worked great before. It works great now.

Edited by Gary jp4

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once you pull the slave off is there only one ball pressed into the piston or is there one in the piston and another between that and the shaft?

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Just one pressed into the piston. That is the one that engages the shaft.

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So, I just went through the process of replacing the O-ring on my slave cylinder piston on my 2001 KTM 520 EXC and followed some of the advice on this thread. Here is some basic info:

1) The slave cylinder piston does indeed take a 23.52mm x 1.78mm nitrile O-ring with 90A durometer. In inches that is 15/16" ID x 1-1/16" OD x 1/16" thickness. I know that the math does not pencil out but that is how the manufacturers list them. The O-ring can be found here: http://www.oringsusa.com/catalog/product_info.php?cPath=26_123_105&products_id=105001390&osCsid=vbs1pdtpfl7p60n73vphvchuu6

2) If you want to run a slightly thicker O-ring for a worn cylinder you can squeeze a 7/8" ID x 1-1/16" OD x 3/32" thickness in there. here is a link: http://www.oringsusa.com/catalog/product_info.php?cPath=26_123_105&products_id=105002310&osCsid=lllidpcqrhr070t81cjq9augm4

I got a master cylinder rebuild kit from KTM for $40 and did that at the same time.

I also did some research on using ATF instead of mineral oil in the Magura hydraulic clutch (I have been running ATF). Apparently some ATF can degrade certain rubber components (seems to have happened in my case) so mineral oil is a safer bet.

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