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Thread: Brake / clutch reservoir

  1. #1
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    Question Brake / clutch reservoir

    E36 M3; I find it bothersome that bleeding the brakes also 'requires' bleeding the clutch to 100% replace the brake fluid. (Or at least requires sucking out the brake fluid from the clutch section of the reservoir.) So I rarely do it.

    What advantage is there for a shared reservoir?
    Any advantage or disadvantage to add a separate reservoir for the clutch?

  2. #2
    NeilM is offline Member BMW E36 M3 Expert
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    I suspect that most people would call into question the term 'requires' even more than you did.

    Relative to the reservoir capacity there's a pretty small amount of brake fluid captured in the clutch system, and each time you use the clutch pedal there's a small exchange of fluid between them. In the long term they're going to mix to some reasonable degree. I'm not suggesting that one should never bleed the clutch circuit (Note to self: bleed clutch circuit this season), but is it anything to spend much time thinking about, much less re-engineering?

    I imagine the reason for manufacturers having combined them is that it's cheap and easy. The reason for de-combining them is the converse.

    Neil
    Last edited by NeilM; 05-03-2015 at 11:30 AM.

  3. #3
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    Good discussion. My only concern is the old fluid in the clutch section contaminating the new super-expensive-everyone-has-to-have-the-latest-greatest-race-brake-fluid-including-me stuff that I bleed my brakes with every 6 months or so. Probably a non issue as you say (I've never had brake problems while using track pads, but I don't want to either.) The other side is that I could see a very simple cheap fix....add a motorcycle type brake fluid reservoir and a custom bracket. Probably $20 total and an hour of tinkering. Probably more time and effort than it'd take to bleed the clutch system a few times, but I'm a tinkerer at heart. If I improve something 1 out of 5 attempts, I consider it a win. I'd never make a living at doing this sort of thing.
    Last edited by aeronaut; 05-03-2015 at 11:50 AM.

  4. #4
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    2.5 year bump!

    Is the small cylindrical section that you see when you open the cap the reservoir for the clutch, and the outer rest of it for the brakes? I have developed a slow leak that is draining the fluid from the outer section and want to make sure that I am investigating the correct system.
    95 cosmoschwartz M3/2/5 : 2012-1/1/2014 (worn rtab's and bald rear tires in the rain)

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  5. #5
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by tsmith25 View Post
    2.5 year bump!

    Is the small cylindrical section that you see when you open the cap the reservoir for the clutch, and the outer rest of it for the brakes?
    No it's not. There might be some little ledge internally, but essentially it's a single bucket of fluid.

    I have developed a slow leak that is draining the fluid from the outer section and want to make sure that I am investigating the correct system.
    Check your driver's side footwell (leaking clutch master cylinder, not uncommon) first, then for drippage from the bell housing (leaking clutch slave cylinder, much less likely). After that it'd be the brake system someplace. Could be as simple as a weeping caliper bleed nipple.

    Neil

  6. #6
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    I haven't bled my clutch in several years, but do the brakes many times per year. Based on how nasty looking the clutch fluid was when I did it recently, there's virtually no mixing of fresh fluid in the reservoir with what's in the clutch system. Non issue.
    '95 M3 S54 Track Toy
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  7. #7
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    Wow, one of MY threads resurrected!

    For the record, I did end up separating the brake and clutch reservoirs on my car.
    Can't say it did anything other than add another thing I have to check. lol. Maybe some piece of mind.

  8. #8
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by aeronaut View Post
    Maybe some piece of mind.
    I can't afford to give up any pieces of my mind. ;-)

    Neil

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