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Old 02-24-2013, 01:42 PM   #1
Sadlsor OP
Studly Adventurer
Joined: Oct 2003
Location: Magic City in the Heart of Dixie
Oddometer: 691
Slave Cylinder 2005.5 Adventure -S

Friday my clutch went out, almost like a light switch. Imperceptible difference, then ...NADA. Mushy lever, stalls in first, etc., etc.

Found the clutch line at the master cylinder was exposed; no fluid covering it.

Adding mineral oil, bleeding at the slave cylinder brought it back... for a very few minutes, then repeat the process. Today I took the whole blooming thing apart, it's clean. No scoring, only dirty oil. First clutch oil change; 38K miles on the bike.

Orings look perfect, and I removed the oil jet which WAS clogged. Now it's clear.

So I didn't replace anything, cleaned and inspected, and reassembled with original parts. Went for a spin in the neighborhood, sure the problem would return. I was not disappointed. (Well, actually I AM disappointed.)

The slave cylinder was obviously glistening with clean mineral oil.

I searched and found about 6 threads on the slave issue, including the Oberon, and I've read about the Evoluzione slave as well. Before I call CJ and order the Obie, is there anything else I could have done? Doesn't *seem* to be the master cylinder leaking.

In the end, I really don't understand how the bleeping thing works. I kinda get what happens at the lever / mc end of the deal, but my owners manual doesn't explain (didn't expect it to), and the HOW, while helpful, still leaves me with questions.

I considered removing the orings from the slave piston and the housing, but figured that would be even more of an exercise in futility.

If the slave cylinder is just toast (remember 38K no-maintenance miles), why isn't it more obvious, and how does it fail with no broke parts? Like when my rotor bolts backed out and shredded my stator? Now THAT was obvious!

OC wisdom?
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Old 02-24-2013, 01:52 PM   #2
Joined: May 2009
Location: Ottawa, Canada
Oddometer: 589
yeah, known issue. Just replace it.
Mine did that 2 years ago, 5 days before leaving on a ride. Bit of a scramble to get one here that fast.

The slave is just a hydraulic cylinder that pushes on the clutch rod. One side of these seem to wear, then the piston can tip in the bore and fluid leaks past and now you have no clutch, just a pump for putting oil on your bike's lower end.
I tried to be smart and spent a lot of time getting new O-rings, etc. Not worth the trouble. Just get a new one a put it in - takes about an hour and flush the reservoir and line thoroughly while you're there.

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Old 02-24-2013, 02:36 PM   #3
Sadlsor OP
Studly Adventurer
Joined: Oct 2003
Location: Magic City in the Heart of Dixie
Oddometer: 691
Thanks, Ed. That's helpful.
One of the related threads I found is RedRupert's redesign of the bushing / bore, IIRC, to address the very circumstance you mention. I didn't read the entire thread...
Can someone tell me the basic difference in an Evoluzione or Oberon vs. the KTM stock unit? I have the impression they generally last longer than stock ones.
Meanwhile guess I'll google "WTF is a slave cylinder" for more detail.
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Old 02-24-2013, 02:55 PM   #4
Joined: Jul 2011
Oddometer: 704
The Sigutech slave = better design than Oberon.

I believe ( based on my firsthand experience ) that as long
as the bore of the OEM slave is not "scored", you can use a new O-ring and the
slave can work well again for a long time. It helps to scuff the bore
with a fine ( gray or white color pad, NOT a maroon or green pad ) Scotch Brite pad
in order to put a bit of a "crosshatch" finish on the bore surface before installing the
piston with the new O-ring into the bore. The idea is to make very fine grooves
perpendicular to the direction of slave piston travel. Cleanliness is essential when
assembling the slave and mounting it, as well as during the bleeding process.

You want to "wipe" the Scotch Brite pad around the circumference of the bore,
but do NOT want to work the pad "in and out" of the bore such as the slave piston
does when it operates. You should not be able to feel the grooves you create with your
fingernail, but the surface finish will be a bit less shiny than it was before wiping it
with the Scotch Brite pad.

For the Magura clutch which requires mineral oil and NOT brake fluid,
I use Pentosin CHF 11S central hydraulic fluid instead of the absurdly
overpriced "Magura Blood". The Pentosin has the advantage of being
synthetic so it won't get too thick at cold temperatures, and any garage
which works on BMW, Audi, or other Germans cars will have some Pentosin
on hand or be able to get it.

The Sigutech slave has multiple O-rings which prevent the piston
"cocking" in the bore of the slave and causing accelerated wear and poor
clutch release action. It is much less likely to fail than an OEM slave.

The manufacturer's website for the Sigutech slave :

Or if you don't want to ship from Germany and
don't mind paying a bit more here is a source in
the US :


It'sNotTheBike screwed with this post 02-24-2013 at 03:15 PM
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Old 02-24-2013, 11:59 PM   #5
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Joined: Nov 2005
Location: East Med, Greece
Oddometer: 4,176
My study on slave cyl

I suggest you have a look in here:

Rubbing the cylinder surface is a NO NO. Confusing the lubrication of the inside of the engine cylinders where there is friction between metallic parts and the friction of rubber on metal. Two different things. I went the workshop road with 3 successful cases.
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Old 02-25-2013, 05:12 AM   #6
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Joined: Sep 2005
Location: Mukwonago, WI
Oddometer: 3,976
Originally Posted by It'sNotTheBike View Post

The Sigutech slave = better design than Oberon.
Have you used both? Why do you feel this is true? Interested in your feedback.

I have about 70,000 miles on my first Oberon install and it's still going strong. I've now installed a Rekluse EXP, so I can no longer use it. It has now been transferred to another bike.

Over the last 4 years of dealing with these, I think I've had 3 returned, all for operator install error when there was a step missed in the install instructions and blew out the back side. (same would happen to any clutch slave) Instructions have now been updated. Overall they have been a great, problem free product to deal with.

Safe travels
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Old 02-25-2013, 06:22 AM   #7
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Joined: Feb 2009
Location: Georgia
Oddometer: 650
The problem with the OEM slave is two-fold.

1.) Single o-ring design, & smaller piston which heats up quickly, and begins to break down the fluid faster, and then the O-ring.

2.) Plastic mounting plate: this part tends to warp & or crack over time and allows moisture to collect which works its way into the slave from the back side.

Evoluzion is out of business so there is one less aftermarket option.

Current aftermarket options: Sigutech-Rekluse-Oberon

Oberon- Sigutech & Rekluse features a 27mm piston which provides better mechanical operation easier pull. Sigutech & Rekluse have double Oring design for improved sealing. Oberon is the only option with a proprietary design that incorporates a Viton SEAL on the piston, not an O-ring. The key difference is longevity, and the sealing surface is superior. Their Viton rubber seal is unique in that it is frozen then CNC machined with a U shape groove to provide a better mechanical seal.

Heres a picture:

The other weak link in the OEM system is the plastic spacer that the slave mounts to. This part over many heat cycles will eventually warp, or crack which allows moisture/water to collect in the small air pocket between the two parts, promoting intrusion into the slave. Oberon has offered an optional CNC billet spacer that solves the problem.

My slave went a 20,000 miles same as Sadisor- with out much warning. Which prompted my search for the best solution, which I believe is Oberon. I bought the bike with 19,500 miles, so I had only 500 miles before it went and not time to get to know what the symptoms might be. But looking back, there are some subtle early warning signs, bike creeps a little when in gear, obvious low fluid in the reservoir, and the leaking oil collects at the mounting spacer( but thats hard to see, since that area is normally gunked with chain oil & dirt)

It appears that the clutch system had never been bled. The bleeder was fused/rusted to the banjo bolt- due to moisture build up in the system. I was able to separate them with heat in a vise, but that part was Cherynobled after that excercise which required the purchase of a new $25 "kit" from KTM which has the banjo bolt, washers, bleeder, and fancy rubber cap for the bleeder. I think the key to longevity of the OEM slave, is flushing the fluid OFTEN- which means annually. The clutch reservoir is very small capacity, and the mineral oil breaks down as there isnt much of it. I think CJ offers an extension to increase the capacity. The bleed process is simple by either back bleeding the system with a syringe and 3/16" pvc tube, or bleeding the system with one of the motion pro 1-way bleeders.

Not sure? Check your reservoir fluid level- remove the 2 screws and inspect the fluid- it should be clear, and should be about 4mm from the top of the edge of the reservoir.

Mineral Oil: Im not sure that $5 bucks is really expensive for 100ml of Magura Blood mineral oil- just about any dealer has it or can get it in a day or two. Its more than enough for a flush & refill. The owners manual recommends Motorex 75, which is about $11 bucks- Ive looked at the MSDS sheets for both brands and cant see any real difference. So $5 bucks is better for me. Ive read that LHM automotive grade mineral oil is excellent- synthetic, but its not easy to find here in the US. Castrol LHM+ is readily available in Europe. I know one guy who used medical grade mineral oil from a pharmacy when his slave failed on a trip. Which ever, the Magura master cylinder internals are sensitive and expensive, so imo- use the magura, its reasonably priced, easy to find, just change it annually.

Upgrading the plastic mount to the CNC Aluminum Oberon might be a good low cost preventative option @ $59 to keep moisture out of the back of the slave. And you can always later add the slave for about $159 if you want easier pull and bulletproof reliability.

ACME Rider Supply also offers Oberon Slaves for LC8 & LC4, Magura blood, Motorex 75, and includes a flush kit with your slave purchase. Its not on their website, so call them if you want to order one.
KTM: 06 KTM950S & 10 KTM450EXC
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Old 02-25-2013, 07:16 AM   #8
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Joined: Oct 2009
Location: Marietta
Oddometer: 119
Clutch Slave

I just installed the Oberon from ACME and I the clutch pull is noticeably easer (may have something to do with a new clutch slave and a fresh bleed). Cant speak for longevity at this point but Im really happy with the quality and ease of installation.
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Old 02-25-2013, 10:19 AM   #9
Sadlsor OP
Studly Adventurer
Joined: Oct 2003
Location: Magic City in the Heart of Dixie
Oddometer: 691

I appreciate all the words. Just called CJ; ordered replacement orings as a temporary workaround, as the orange Oberon I desire is slated for a new production run and is presently out of stock. Obviously it's the ...ahem... "fastest" color.

May be a couple of days for the 'rings to arrive, but I could easily quadruple the cost just in Jeep gas, running around town looking for the right size. Not exactly a common need I have, so while they *may* be nearby, I'll just try to chill.

Besides, we're gonna get hit for 2 days with the liquid snow coming in from the west. So, Texans... y'all got yer tires studded for riding in the white stuff?
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