LC 4 Clutch O-rings

Discussion in 'Thumpers' started by gunnerbuck, May 15, 2009.

  1. gunnerbuck

    gunnerbuck Island Hopper

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    My hydraulic clutch has been working below par for a while so I decided to look into it.... Seems as I just rebuilt the master last summer I figured the problem lies with the slave.....

    The slave is very simple with only three parts to keep track of, the body, the piston and the spring...

    The piston uses an o-ring which seals it against the cylinder and upon inspection my o-ring looked pretty worn.... KTM/ Magura doesn't offer a replacement for this O-ring in the parts book because they want you to fork out $100 for a new piston... I figured I would just go through my standard and metric O-ring kits and easily find a replacement.... Not so... everything I have is too thick for that diameter....

    I then dug through my stock of replacement parts and found that the countershaft seal O-ring {silicone} looks to be the same size.... I fired it in, put things back together and purged the air from the system... The result is that the clutch action is right back to normal, but for how long? Will that softer silicone O-ring hold up?

    Anyone else replace the o-ring in their slave?
    #1
  2. dlh62c

    dlh62c Long timer

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    No I haven't, but the thought has crossed my mind.

    Mine went out this spring. I ended up forking out the $100 dollars and replaced the slave cylinder. Little did I know I had to break the chain to remove it. Looking back,for the effort it took to replace it, the $100 was well spent. But that's just my opinion. Riding this bike with a non working clutch SUCKS!

    Please let us all know if it works. I have a bad one with only 15,000 miles on it. Which I'm sure just needs a seal.

    daryl
    #2
  3. gunnerbuck

    gunnerbuck Island Hopper

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    Rather than taking the chain apart, I just slid the counter sprocket off the shaft and then was able to pull it out from under the chain... I did this without having to loosen the rear wheel to gain extra chain slack...

    I picked up a used slave for a spare but it is in no better condition than my stocker... I'm up to 90,000 KM on the original now so I guess it's over due to be acting up....
    #3
  4. Cruiser

    Cruiser Cruiser.. 16 beta 350rr, 04 KTM 525sx/exc FS

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    I used silicon o-rings on the slave on my 03 and 97 gasgas,, with no issue whatsoever,, Keep up posted on how these work out for you..
    #4
  5. meat popsicle

    meat popsicle Ignostic

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    Some links from here and beyond that may be of assistance:

    Hebo Kit on a KX (scroll down for some talk about o-rings:
    http://www.john-stichnoth.com/Hebo.html
    Maybe the Hebo o-rings are the right size? :dunno Available in a repair kit.

    43102 Slave Cylinder, Magura, Hydraulic Clutch Slave Cylinder for the Magura hydraulic clutch assemblies $59.00
    http://www.blackwidowatv.com/pix/2008BWATVCatalog.pdf
    Maybe there is more than one? or KTM markup is 100%...

    Brake fluid eats Magura seals... and brake system o-rings are silicone (or is that DOT 5.1 :tb)
    http://www.southbayriders.com/forums/showthread.php?t=74948
    Probably not your potential issue.

    The UK bloke did know which size it was... but he never 'membered:
    http://ktmforum.co.uk/showthread.php?t=33137
    :bluduh

    If you do get a new clutch slave then maybe you should Evoluzione...
    http://www.advrider.com/forums/showthread.php?t=234490
    A new design on the slave, for the 950 (but it probably works eh?)

    Cheap o-rings bought ten at a time:
    http://www.advrider.com/forums/showthread.php?t=171986
    hmmm...

    The o-ring is flat on one side?
    http://www.thumpertalk.com/forum/archive/index.php/t-416911.html
    :dunno

    Sorry, no holy grail for you gunnerbuck.
    #5
  6. gunnerbuck

    gunnerbuck Island Hopper

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    Thanks Meat for taking the time, some interesting stuff....

    [​IMG]

    Here's a photo of the parts in question... The silicone countershaft O-rings have a slight bit larger hoop diameter than the original in the picture but perform perfectly... My clutch feels like it did new....

    I always pack a spare countershaft O-ring on road trips so it's good to know that it will also work in the slave... I'll throw in a couple from now on....

    Filling and bleeding
    [​IMG]
    Take the master cover off...
    [​IMG]
    First fill the slave base with mineral oil if stock (I am using fork oil in my clutches}, then coat the bleed screw threads with some grease to stop air infiltration... Then using a syringe, vacuum up some mineral oil then push it up through the slave bleed screw to the master to force all the air up ahead of the oil..
    [​IMG]
    Keep an eye on the oil level so it doesn't over flow... Oil level correct then squeeze the lever a bunch of times, it should come up stiff... If it doesn't, it likely still has air in the system so you can try again... First suck the oil out of the master, then repeat the process...
    #6
  7. wrk2surf

    wrk2surf on the gas or brakes

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    I will dig up my old one but what happens is the coating on the cover where the oring rubs actually takes the coating off and makes the oring fix a no-go.. then you need the whole new kit... mine lasted about 2 orings.. on my second cover now and 2nd oring.. looks like I will be needing to order another...
    #7
  8. gunnerbuck

    gunnerbuck Island Hopper

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    Wow, you must work you clutch pretty hard, how many miles do you figure the original gave you?
    #8
  9. dlh62c

    dlh62c Long timer

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    I popped the piston out of my bad slave cylinder over the weekend. There didn't appear to be any wear on the o-ring or the cylinder walls, but the o-ring was hard as a rock. There was no elasticity at all in it.

    daryl
    #9
  10. gunnerbuck

    gunnerbuck Island Hopper

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    That was the same for my 2 slaves, only the O-rings appeared shot....

    I think if you replace the O-ring with one of a thicker type it will wear out the slave cylinder wall prematurely.... I believe the stock one is 2MM and most kits offer 2.5-3mm in the required hoop size.... Of course one could try the old trial and error trick of stretching out a smaller O-ring onto a broom handle until you get one that mirrors the slave unit... But I don't think a stressed O-ring will last long....
    #10
  11. wrk2surf

    wrk2surf on the gas or brakes

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    10-15 thousand mi... probably 20,000 for the new slave cover..but I just rebulit the motor a month ago and have 1,500 mi ..ride alot .. and hard...
    #11
  12. makazica

    makazica Been here awhile

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    Gentleman,

    recently I purchased a Magura hydraulic clutch. From the past posts I found out that there are two versions available out there....I'm not sure which one I have so I'll post pics later today with hope in indentifying it.

    As I understand, one is a perfect match and the other needs a bit of a filing job....which is no problem for me.

    Before I install it, I would like to know a couple of things:

    1. As I have bar risers installed (28mm SWMotech), is the line going to be long enough to reach all the way required?

    2. Could somebody instruct me in the procedure of bleeding the clutch system?

    3. Could somebody please post a pic of their installation?

    4. What fluid goes in the system and what is the price for a bottle?

    Thanks!
    M.


    This is the one I got:
    [​IMG]

    Help please...!
    #12
  13. wrk2surf

    wrk2surf on the gas or brakes

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    have to try to route the hose dont know unless you try.

    see the syringe ..you bleed from the bottom with it..


    mineral oil...
    magura blood
    #13
  14. wrk2surf

    wrk2surf on the gas or brakes

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    has the 2MM question been answered and did the counter shaft oring work
    gunnerbuck???

    mines leaking and dont have any orings .. need to go to da stoe
    #14
  15. claferal

    claferal Been here awhile

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    It is better to use a o ring made of NBR70. The silicone seals fails because the silicone is damaged by the mineral oil. This problem also happens in the LC8 and we has tested silicone seals with problems after some days of use.

    Put a silicone seal in a glass with oil and it will become larger in one day
    #15
  16. joekanter

    joekanter Been here awhile

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    ---my 07 640A with 5K miles had the clutch take a dump. Being lazy, short of time and a little freaked out with my ordeal to get home, I took the bike to the dealer. Their mechanic says that the master and slave are fine. Suggested that the mineral oil was shot and that it simply needed to be replaced. He went on to say that if the slave was beat, then when the new oil was filled-it would fail immediately. Suggested that the oil should be changed out twice a year. I have not changed the mineral oil, its the same stuff from the factory. He said that the mineral oil that was left in the slave was cloudy and shot. I'll pick up the bike tomorrow but I'm feeling a little less confident.

    In the event that the clutch goes again, I'll try to tackle the slave rebuild. One question-when using the syringe to pressurize the system, do you loosen the master cover or leave it tight (I think there is a over flow?)

    Thanks guys.
    #16
  17. gunnerbuck

    gunnerbuck Island Hopper

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    Take the master cover off so you can keep an eye on the oil level.... I used a squeeze bottle to suction oil out before it spilled over the top and then to adjust the level to mid reservoir before finishing up ....
    #17
  18. gunnerbuck

    gunnerbuck Island Hopper

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    The silicone o-ring I put in has worked perfect for nearly 12,000 km now....

    I'll report the mileage when it fails...
    #18
  19. GodSilla

    GodSilla I did that.

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    From memory the KTM manual specifies to remove the bleeder on the clutch slave and replace it with a reverse bleeder, bleed from the bottom up, then remove reverse bleeder and replace with the stocker. Bugger that.
    I just bled mine like a regular hydraulic brake on a bike, fluid in the master cylinder and bleed from the bottom, works fine for me.
    #19
  20. bikepikespeak.com

    bikepikespeak.com Been here awhile

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    I had my clutch go out on me. Sounds like the same situation. Took the slave off today in hopes of replacing this o ring everyone's talking about. I can't figure out how to pop the piston out to get to it though. Any tips? And how do i know when I see it if it was bad and this was the problem?
    #20