Magura Brake Bleeding

Discussion in 'Recumbent bicycles' started by Brent Hugh, Apr 27, 2003.

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  1. Brent Hugh

    Brent Hugh Guest

    >It's time I tackled the brakes on the Screamer, what with warm weather just around the
    >corner (maybe).

    >The actuation point for the front brake (Magura hydraulic rim brake, model HS 11, I think) has
    >always been a little close the the handgrip. Brakes have been sufficiently grippy, though, so I've
    >let them be.

    >I'd like to get them balanced up with the rear so I'm looking for tips and techinques for filling
    >and bleeding.

    I got messing around with the Magura brakes on my Screamer last weekend, after we went for a ride
    (in the rain . . . ) and the brakes seemed to not have quite enough stopping power even when the
    levers were pulled until they blocked against the handlebar.

    Like you, I first thought of changing the brake fluid and topping it up to a higher level. And I
    thought of turning the brake pad adjustment to make the pads go closer to the rims (but that didn't
    really help--it moved the pads clower but simultaneously moved the brake lever closer to the
    handlebar, so although there was less motion before the brake pad contacted the rim, there was also
    less travel distance left before the brake lever contacted the handlebar . . . altogether, the two
    effects pretty much cancelled each other out).

    But what I discovered is that there are quite a lot of mechanical adjustments to the brakes that
    allow you to take up that extra motion without messing with the brake fluid. Magura brakes are
    designed to fit a wide variety of wide & narrow rims, so it's no surprise there is some adjustment
    there. Paqe 7 of Magura's 2003 rim brake workshop manual shows how to make a lot of those
    adjustments:

    http://download.magura.de/felgen_03_e.pdf http://www.magura.com/english/frameset/default.htm

    It's possible that these adjustments were never set up correctly for your particular bike/rim.

    But what I found, in my case, is that each side of the brakes has a little elbow that is supposed to
    be adjusted so that it blocks against the fork or the frame at all times. This little elbow is very
    important, because when you squeeze the brakes, tremendous outward force is created and this force
    is transferred to the fork/frame via these elbows and the brake studs.

    If the elbows are not contacting the fork/frame, then the entire brake assembly can rotate around
    the brake stud, which has the effect of taking the brake pad further away from the rim and creating
    a lot of extra "lost motion" in the brake system. What it feels like from the driver's seat, is that
    the brakes are very weak and never have enough stopping power, even though you've pulled the lever
    all the way back to the handlebar.

    On my bike, these elbows are silver; in Magura's workshop manual they are black. Mine originally
    had little plastic sleeves on them. The sleeves have fallen off somewhere along the lines,
    giving about a
    1/4-inch gap between the elbow and the fork/frame. This is probably the root cause of the problem.

    As the workshop manual says (at least three times!):

    "The black elbows (arrow 1) are adjustable and point preferably downwards (for better tire
    clearance!). They MUST ALWAYS block against the fork or frame." [page 7 of 2003 workshop manual]

    My rear brakes also have the brake booster (a very good idea, I understand). It has some width
    adjustibility built into it, too, and I had to loosen it and re-tighten it in a closer
    (narrower) position.

    After making all these adjustments, the brakes feel much better--and all without messing with the
    brake fluid at all . . .

    --Brent

    bhugh (at) mwsc.edu

    +++++Missouri Bicycle Federation: http://www.MoBikeFed.org+++++ ++++Music of the Human Genome:
    http://mp3.com/brent_d_hugh++++
     
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