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Thread: Brake bleeding

  1. #1
    Senior Member ken nougaret's Avatar
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    Default Brake bleeding

    I pushed 5606 up both brakes 3 times each side alternating sides. I'm still left with this 2" section of air. I used the oil can and the syringe with the same results. Thoughts?
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  2. #2
    Senior Member HighWing's Avatar
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    Default Re: Brake bleeding

    Ken,
    I'm not sure what I am looking at. My lines go up through the bottom fabric then across the floorboard near the cowl side then on the floorboard around the corner then up to the brake. In bleeding all is uphill from the caliper - especially with tailwheel. I don't understand the line to the top of the tube then back down.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  3. #3
    Senior Member Dave S's Avatar
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    Default Re: Brake bleeding

    Ken,

    Wondering if the orientation (line entering from the top of the fitting rather than the side or bottom) of the blue "T" could be the cause of the issue? If there is a large enough void inside the "T" could it possibly be holding a air bubble while allowing the more dense fluid to slip past into the reservoir? Just a thought.

    Before making a lot of work of it, I'd go back to the brake wheel cylinder this line is connected to and give it another go. I found it useful to hook up a spillover line to the top of the reservoir and then not worry about excess fluid spillover. Possibly a little more forceful application of the oil can or syringe may blow the bubble into the reservoir out of the line? Another experiment may be to have two people applying a syringe to both sides at the same time.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4
    Senior Member ken nougaret's Avatar
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    Default Re: Brake bleeding

    Lowell, your question prompted me back to the manual to take a picture for you. And Dave I suspected the same as you. After looking at the pic again, I see that I have the tee upside down. How did I do that? Thanks for the quick reply. I will flip the tee over and try again.
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  5. #5
    Senior Member ken nougaret's Avatar
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    Default Re: Brake bleeding

    Success! And I feel stupid. Thanks again, Ken

  6. #6
    Senior Member
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    Default Re: Brake bleeding

    Ken,

    I wouldn't feel stupid (but I know what you mean). You pointed out a few good things for everyone.

    1. The value of asking questions as opposed to willy nilly going at it and getting frustrated with it and wasting time trying to figure it out or worse, leaving it and moving along.

    2. The value of experience here and on a few other forums.

    3. The value of at least one extra sets of eyes.

    4. The value of "a picture is worth a thousand words".

    Stupid would have been to not ask or doing it wrong twice!

    Show me someone who hasn't made a mistake and I'll show you a liar!

    Sounds like your getting closer, can't wait to see her done!

    Greg

  7. #7

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    Default Re: Brake bleeding

    What difference does air near the reservoir make? as long as it doesn't make it to the master cylinder.
    The important part of bleeding the brakes is (if I understand correctly) that no air is in the lines between the wheel pistons and the master brake cylinders. This makes ''mushy'' brakes.

    Ofer Gd

  8. #8
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    Default Re: Brake bleeding

    I'll take a stab at this:

    Brake fluid is relatively incompressible, but it does expand as it gets hot. Also the fluid behind the master cylinder moves in both directions. Sucked towards the master cylinder when the brake is applied and back to the reservoir when the brake is released.

    It is possible to suck the air pocket into the cylinder (not likely though).

    The air pocket could also block the return flow of fluid to the reservoir, causing the brake to not fully release (also not likely). That is more likely though if the fluid heats up and expands and has no where to go.

    Most likely though, the air pocket will just move back and forth in the line - I wouldn't count on it though! As Murphys Law says the time that doesn't happen is the one when you have a hot landing to far down the runway!

    No air in the brake system - except in the space on top of the fluid in the reservoir where you fill and check level.

    Greg

  9. #9

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    Default Re: Brake bleeding

    I agree to most of your post but not to the part that says the air bubble can block the flow.
    I definitely agree that these problem should be solved (and was) but if the line between this fitting to the cylinder is long enough and the fluid does not get to the cylinder when the brake is depressed, there is no real problem.

    Ofer Gd

  10. #10
    Senior Member jiott's Avatar
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    Default Re: Brake bleeding

    I also seem to have a small bubble of air in one of the lines right at the reservoir. It wasn't there to begin with (3 years ago) but seemed to slowly form over time. I suppose I should rebleed the brakes and get rid of it. When I first noticed it I applied both brakes by hand while watching the bubble up under the dash. It moved down some but nowhere near the master cylinders. Since the brakes have always felt fine, I quit worrying about it, taking the attitude of ofergd. However, I agree with Danzer, it is best to get rid of it and I will one of these days when I am working on that part of the aircraft.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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