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Thread: brake fluid in clutch

  1. #1
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    brake fluid in clutch

    I mistakenly flushed my clutch with brake fluid a few months ago. It felt different so I tryed to bleed it again when I let the resevoir run dry. It was then that I realized I should have been using mineral oil. I tried to flush it with mineral oil but can't seem to be able to get the clutch cylinder to pump. Have I ruined the handlebar and slave cylinders? Can either one be rebuilt or just replaced?

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    brake fluid will swell the rubber bits. Some times the rubber bits can be cleaned and will shrink as the brake fluid evaporates, with could take weeks or months. you probably need to replace all, including the lines.

    Rod

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    The system is filled from the fitting at the bottom near the slave. If you've had a system with wrong stuff in it for a long period there is a good chance you've damaged it but short of doing a flushing refill / test or a disassembly inspection there is no way to be certain. The cheap way out is to properly refill and hope for no leaks/ damge, A more cautious way is to hunt rebuild parts for the master and fit a new slave - this may be a dealer job for you..

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    If you have a stainless clutch line, its inerior liner is impervious to both clutch and brake fluid so should not need replacement BUT you do need to run enough fluid up the line to flush it. If the line is rubber, it will probably not be compatible with brake fluid and should be replaced.

  5. #5
    Nickname: Droid
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    That's right about the hose assembly, which I believe is a teflon lined S/S braided hose. The hose is not affected by the fluid. But the seals in the system "may" be affected. One way to find out is to research the part numbers for the seals, if those are available as individual part numbers.

    If the part numbers are the same for the seals in the clutch system as in the brake system, it would indicate the seals are not the issue. But if the part numbers are different, and the seal material is different, then very likely the seals have to be replaced if a thorough system flushing does not correct the issues.

    Not sure if flushing the system from the slave up to the master with Acetone or mineral spirits, or some other form of liquid solvent would clear the brake fluid from the system, and then flush again with vegetable oil. May be worth a try.

  6. #6
    Barback King rapiddog's Avatar
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    falsealarmism

    ...I doubt you have to worry about damage. Just get it flushed out with plenty of the correct fluid and you should be good to go.
    No point in replacing what's not broke.

    You've already paid enough by admitting what an idiot stunt you've done to all of use here...
    I'm just glad I read this post...I was about to do the same thing...
    "...the burble of my exhaust unwound like a long cord behind me. Soon my speed snapped it, and I heard only the cry of the wind...." Larry of Arubia

  7. #7
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    I hope I can save some of this system. I've checked the prices of clutch cylinder, hose slave cylinder and hose and it comes to almost $800. I'm going to try to flush and bleed system with correct fluid and go from there. The clutch cylinder is $370 and I know it could be rebuilt but I don't think anyone sells seals for it.

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    I had a friend with a 10 year old car. It got power steering fluid added to the brake my mistake.

    With parts and labor, it was totaled. Rebuilt master cylinder, brake proportioning valve, all calipers, needed some new rotors when the brakes locked , all flex hoses, remove ABS, was going to be well over 1000 on a 10 year old car.

    Rod

  9. #9
    jeepinbanditrider
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    The R bikes use mineral oil in the clutch systems??? WTF BMW?

  10. #10
    got, got, got no time... rguy's Avatar
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    Denatured alcohol would be the only solvent I would consider flushing with. I have used it successfully to flush old calipers without disassembling them. It worked fine and did not harm the seals (30 year old calipers and no leaks - knock on wood). Do not use anything petroleum based.
    Neal - '09 R1200GS / '81 R65
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  11. #11
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    Try flushing it with lots of the right fluid and you "might" be lucky. This is not simply a case of "don't fix what aint broke" because again, it depends on the seal materials used in the clutch system versus the brake system. IF, if the seals in the clutch system are not compatible with brake fluid,(this is from my 18 years of experience with fluid problems in hydraulic hoses, much the same materials), most likely the brake fluid attacks the seals it causes them to swell. When they swell the clutch either doesn't release or doesn't engage.

    Once swollen, they do not come back to their original state no matter how much flushing you do. Again, it depends on if the seals are different in the two systems. Sure, try the flush, either with the correct fluid or maybe first with denatured alcohol and then the right fluid. Nothing to loose there but your time. If it works, great you're done. If not, THEN you have reason to tear it all apart.

    Now, the reason BMW went to mineral based fluid in the clutch system was because if it gets on the dry clutch friction plate it does not ruin the clutch. Earlier versions of the hydraulic clutch on the Oilheads/Hexheads that used brake fluid in the clutch system had a leak problem at the slave cylinder. When it leaked it oiled the friction plate with brake fluid and ruined the clutch, slipparooo! Mineral oil does not fully ruin the friction plate if the slave cylinder develops a leak. Dino based oil, mineral oil, vegetable oil, water, heck even glycol works as "hydraulic" oil because the hydraulic part is not the oil, but the use of fluid to transmit motion and power.

    Another reason I prefer the good ol' clutch cable on my 76 and 94 BMW's. Simple. It works. You can adjust it. You know when it doesn't work and most often why it doesn't work (cause you can see it). You can repair/replace it in a hotel or Walmart parking lot with hand tools in the tool kit. Ahh,....progress?

  12. #12
    Cam Killer marchyman's Avatar
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    Quote Originally Posted by Downs View Post
    The R bikes use mineral oil in the clutch systems??? WTF BMW?
    Yeah, using hydraulic fluid for a hydraulic application... what where they thinking.

    Unlike brakes the clutch doesn't get all that hot. There is no need for the high temperature characteristics of brake fluid. Hydraulic fluid (and that's what the "mineral oil" mentioned is) isn't hydrophilic. It doesn't get old and water logged like brake fluid. In the last 75K miles the most I've had to do with my clutch is pull a bit of fluid out of the master cylinder now and then as clutch wear causes it to go above the MAX mark.

  13. #13
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    It is true that seal dameage if it has happened is likely welling. But that can also lead to early deterioration - even if a flush successfully restores system function.
    It is useful to remember that really big ticket item that could happen as a result of this episode is a significant leak / failure at the slave cylinder which will oil the clutch disc and require a clutch replacment. That is a bitch job needing lots of tie to get at the parts- pretty simple once you get there. Not at all cheap at a dealership due to labor hours needed.
    Getting the slave out and making sure it is in good shape might be useful insurance against a well over $1000 clutch job.

    If this were mine I'd pull the slave and inspect/repair/replace as needed, then flush from the bottom.

  14. #14
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    Maybe they didn't need to use brake fluid in this application but in the interest of making things simpler and more idiot proof, I wish they would have. Is mineral oil any better than brake fluid in this application? After I did this, I looked in my owners manual. It doesn't say anything about what fluid to use only to take it to a dealer if the fluid is low. On the cap it does say to only use mineral oil. It's my own fault for not making sure which fluid to use first.

  15. #15
    jeepinbanditrider
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    Quote Originally Posted by marchyman View Post
    Yeah, using hydraulic fluid for a hydraulic application... what where they thinking.

    Unlike brakes the clutch doesn't get all that hot. There is no need for the high temperature characteristics of brake fluid. Hydraulic fluid (and that's what the "mineral oil" mentioned is) isn't hydrophilic. It doesn't get old and water logged like brake fluid. In the last 75K miles the most I've had to do with my clutch is pull a bit of fluid out of the master cylinder now and then as clutch wear causes it to go above the MAX mark.
    Interesting. How many other manuf use Brake fluid in the brakes and hyd fluid in the clutch systems? I've never seen anyone else that does. Seems like for simplicity you'd use the same fluid the other hydraulic system (brakes) uses.

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