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Clutch fluid on 09 RT

gateway guy

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I mistakenly changed fluids on my RT without checking a manual and put brake fluid in the clutch hydraulics. Did I ruin anything, and will a flush and refill with the proper mineral fluid fix this. I rode the bike in 40 degree weather and the clutch slipped until the engine warmed, also the clutch lever felt like mush.

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Sounds like air in there too. Flush out the stuff a couple of times. I do not know if the seals and hose are compatible with brake fluid but possibly not. The main reason they switched to mineral oil is that the clutch oil does not need the specs of heat resistance and such that brakes do and with this the mineral oil does not take on water like brake fluid. Thus long times between changes, 4 years? But in your case much shorter times. I would give the dealer a call and when the service counter guy answers you lead in with "my buddy did a strange thing ...... (the mineral oil hydraulic fluid is becoming more common. I saw a Castrol container of it the other day at the auto shop) Please let us know the end story, thanks.

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Morning gateway guy


On the 1200RT both the master cylinder and slave cylinder fluid seals are designed to be used with mineral oil not brake fluid so brake fluid can (and often does) soften and swell the seals. This makes the seals drag in the bores and could even make them hang up, stick, or leak.


I really don’t know if a couple of system flushing’s with mineral oil will allow the seals to return to normal or you have damaged them for good. In the auto industry when this happens we always replace the seals with new or replace the master cylinder and slave cylinder with new units.


Unfortunately on the 1200 RT there is always the chance that the slave cylinder will leak (either now or in the near future) therefore contaminating the clutch. That can get expensive in a hurry.


I really don’t know what to tell you on your problem, the “right thing” to do is flush the system out real good then install a new slave cylinder and rebuild or replace the master cylinder. Then flush the system once more.

Or at least flush the system out real good then replace the slave cylinder as you can’t see that leak until it’s too late.


At the very least remove the slave cylinder and look for signs of fluid leakage at the push rod end. If OK “now” flush the system out using mineral oil then ride a for it a while, then remove the slave cylinder again for another look for signs of fluid leakage. Any signs of leakage at all best to replace the slave cylinder.


If, after flushing the system a few times and no leaks present you still have a sticking or mushy feeling clutch you will still probably have to replace the slave cylinder and replace or rebuild the master cylinder.


If this were my bike I would first call my insurance company to see if this type of issue is covered (I have seen it covered in some auto situations).


If not.


Then I would definitely flush the heck out of the system, then replace the slave cylinder. On the master cylinder I would see if a rebuild kit or new seals were available and if so rebuild the master cylinder. If no new seals available then also replace the master cylinder.


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As dirtrider indicated, you need to do more than just flush fluid. Your seals will not return to "normal."


Replace the master, fluid line, and slave. GET THE MANUAL!! You do not just dump fluid in at the master and bleed. On the GT a reverse flush is required else you get air in the system that you can't get out very easily. Trust me, I know!! This is what my dealer screwed up on eventually causing BMW to buy my bike back. Long story!


Mineral oil has no service interval on these systems. The fluid is not hygroscopic.


Lesson learned, unfortunately, it's an expensive one. It will be much more expensive when your slave fails and you now have to buy a new clutch.

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I removed the slave cylinder and it was leaking pretty badly so it needs to be rebuilt if parts are available. The push rod for the pressure plate was wet near the slave cylinder but dry farther in toward the clutch. I haven't taken the master cylinder apart to see how it looks. Is it possible the master cylinder could survive, the gasket under the lid looked OK.

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Your slave has already died and you're gonna try and save the contaminated master?


Lesson learned, replace, do not rebuild, reassemble properly, move on.


You are jumping over a dollar to save a dime.

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As this same query was posted by the same poster on the MOA list, I'll point people over there: http://www.bmwmoa.org/forum/showthread.php?p=636879#post636879 and my response is exactly the same (this is going to get expensive real fast):


This is a case where I'd be searching for a rebuild kit for the master cylinder, and a replacement for the clutch slave cylinder. I wouldn't trust those seals once they came in contact with brake fluid. Hopefully Magurra carries a rebuild kit for the master cylinder (they are obscenely expensive new.)


The slipping pretty much indicates the clutch has gotten wet with brake fluid. If so - after replacing the clutch cylinder, I'd remove the starter (after disabling the coils and injectors - IE - unplug them), and start spraying some brake cleaner into the opening while rotating the engine and pulling in the clutch (or rotating the rear wheel with the transmission in gear if you're not ambitious enough to remove the alternator cover so you can get to the crankshaft nut..)


I would do this OUTSIDE since brake cleaner tends to be flammable stuff, and I'd let it dry at least overnight before reinstalling the starter and trying to start it. If you still smell the cleaner sniffing at the starter hole - wait until you don't.


Since we now have a posting indicating the clutch slave was leaking, and reported slipping it isn't a case of maybe - it's a case of the clutch IS contaminated.


This means a new clutch slave and at least a rebuild (if the parts are available) of the master cylinder are needed. It also means the clutch itself (disk and friction surfaces) have to be cleaned out.


Dunno if spraying brake cleaner into the housing at the clutch surfaces will do any good, but the cost of trying it is minimal compared to a complete clutch disassembly and replacement. I do know of cases where an oil soaked clutch disk was restored to good working order using brake cleaner.


One problem that may arise if this does work is it may wash lubricant off the clutch splines.


Or it may not work at all. In that case, this is going to be an expensive repair.

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Morning Don


Gateway Guy reported “The push rod for the pressure plate was wet near the slave cylinder but dry farther in toward the clutch”

There was also an earlier mention of “also the clutch lever felt like mush”.


Hopefully that means the fluid didn’t get very far into the clutch area. Hopefully his clutch slipping issue was just caused by swelled up piston seals causing the clutch to not fully engage quickly.



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I'd give that a big "I hope so.." - but wouldn't count on it. Paul Glaves pointed out on the MOA list (in GG's thread there) that when the slave cylinder leaks, it often takes out the transmission input seal.


At the least - after the hydraulics are sorted out - use of a boroscope in the clutch area might tell us how bad it really is. Or it might be obvious if the starter is pulled.


Anyway - it's a good reminder of what not to do, and why sometimes DIY can turn around and bite us in the butt..

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I think my clutch slipping was due to the seals swelling because when I took apart the master cylinder the piston would stick and slowly release. Went to the dealer and no rebuild parts available for either master or slave cylinder. I emailed Magura and have not gotten a response so far. Looking on ebay for parts as dealer prices are in the stratosphere. An expensive lesson learned.

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I didn't think the clutch slave was all that pricey- the brake setup certainly is without a rebuild kit. BMW has been criticized before for failure to have these parts available- don't know why they don't, especially for the master.


If you get anything useful from Magura, please post it.


Other people have certainly made this error the same way folks commonly put wrong fluids in power steering systems. You're one of the rare few to admit it....

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