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Thread: Brake bleeding

  1. #1

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    Brake bleeding

    I have a set of Matoc MC-4 master cylinders and and Matco W 600 XLT brakes on my Back Country Cub project. Today I add brake fluid (pumped in from the bottom) until the reservior was full. I pumped and pumped the brakes and nothing. I pumped more and bleed them, added more fluid and still no brakes. If I pump the master cylinder rapidly about a deozen`times I get a little brake. Played this game numerous times with Clevelands and always won. I don't seem to be able to get all the air out of these. I was hoping some of the experts out there could offer up some of their wisdom.

    Thanks, Randy

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    always DRAIN all fluid out... then refill only from bottom... once you have an air bubble stuck/trapped in system it will be a pain to try to 'bleed' it out.... way faster to drain, and fill it FAST..(use a garden sprayer pressure pot if you have problems)

  3. #3
    www.SkupTech.com mike mcs repair's Avatar
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    also if calipers are not FREE to float in mounting post holes or brake line is holing them in a BOUND position you will just be flexing caliper before brake pads make solid contact giving you a good brake......

  4. #4
    irishfield's Avatar
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    What Mike says! Drain them completely.. crack the bleeder and pump them until everything is dry. Fill from the bottom being certain you don't put an air bubble in at any point. I slip the 1/4" wrench on first.. bleed the feeding hose until it's air free, slip over the bleeder.. crack the fitting and pump until fluid hits the reservoir. Repeat on the other side.

    I use an electric windshield washer pump with the inlet hose stuffed in full jug of fluid and 1/4" clear aquarium hose on the outlet. Same pump has lasted over 15 years and done many many system fills on wheels and long lines of amphibs.

  5. #5
    Steve's Aircraft (Brian)'s Avatar
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    If those cylinders are mounted horizontally to the frame, then you need to remove them with the lines connected and tilt them vertically to get the air out of them while bleeding the system. If they are vertical, then you have air entrapment. I would break loose the outlet fitting to get any air out at that point and then fill the system up.

    Brian.

  6. #6
    Steve Pierce's Avatar
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    What Brian said. I raise the tail up but still end up having to take the cylinder out to get the cylinder in a position to get the air out. Usually can just remove the aft 3/16" bolt and raise it up. I use locktite on the bolt going back in. I also use a clear hose from the reservoir into a jar. I don't drain the whole system. I use a garden sprayer with a shut off valve to push the fluid up from the bottom and watch the hose at the reservoir for air bubbles. I let it flow for quite a while after I see the last bubbles. If it is being difficult I have had success with pushing the pedal slowly while bleeding and gotten the last little bit of air out.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  7. #7
    Flying Miss Daisy's Avatar
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    When dealing with Brians boosters what is the second bleeder on the booster for? I use it to dampen the sensitivity of the booster. Do you need to drain these boosters in entirety if you are not having large issues as I have only a soft sponge feel after the winter.
    John
    Life should not be a journey to the grave with the intention to arrive safely in a well preserved body but rather to slide in sideways, well used up proclaiming "WOW What a Ride"

  8. #8
    behindpropellers's Avatar
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    I have used one of those vacuum suckers a couple times. Works pretty good. No mess.

    Tim
    Piper J-5A C-90 N40877
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  9. #9
    irishfield's Avatar
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    Here is a picture of my "system". All in one tote tray. Old battery, pump, fluid and supplies. Easy to store and everything is in one place when needed.
    Attached Images Attached Images

  10. #10
    Steve Pierce's Avatar
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    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  11. #11
    Steve Pierce's Avatar
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    Quote Originally Posted by Flying Miss Daisy View Post
    When dealing with Brians boosters what is the second bleeder on the booster for? I use it to dampen the sensitivity of the booster. Do you need to drain these boosters in entirety if you are not having large issues as I have only a soft sponge feel after the winter.
    John
    John, I don't have the instructions handy but I remember there being a place to trap air there and they want you to crack that bleeder to eliminate the entrapment when bleeding the entire system.
    Steve Pierce

    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  12. #12
    Steve's Aircraft (Brian)'s Avatar
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    Quote Originally Posted by Flying Miss Daisy View Post
    When dealing with Brians boosters what is the second bleeder on the booster for? I use it to dampen the sensitivity of the booster. Do you need to drain these boosters in entirety if you are not having large issues as I have only a soft sponge feel after the winter.
    John
    John,

    That is there to bleed out entraped air in the cylinder. Otherwise, you get a soft pedal. Here are the bleeding procedures for cubs. Note items 5, 6, 7, 9 and 10.


    Bleeding procedure for Cubs:

    1. Remove cap from reservoir to observe fluid level.
    2. Close bleed valve on master cylinder.
    3. Attach pressure vessel at the wheel, and pump fluid up through master cylinder into reservoir, until full.
    4. Close off bleeder at wheel and disconnect pressure vessel.
    5. Open bleeder at master cylinder and allow fluid to bleed out from reservoir until fluid is observed exiting out of bleeder valve.
    6. Replenish reservoir and pump up pressure with pedal by hand, hold pressure, and crack bleeder valve on master to allow air to escape. This is similar to bleeding your car brakes. Continue process until all air is purged, and pedal becomes hard.
    7. Once air is purged from master, air can still be trapped back at the brake cylinders at the wheel. If brake feels soft, push pedal down and lock parking brake, then crack bleeder at wheel cylinder to allow any trapped air to escape. Release parking brake to allow fluid to replenish in master from reservoir. May require more than one attempt to purge all the air. Use a second person is no parking brake valve is installed.
    8.Replenish the reservoir and replace cap.
    9. You may need to crack the bleeder valves a second time after aircraft has set overnight.
    10. “CAUTION” all the air must be removed before brake will work correctly. A “soft” brake usually means air is trapped somewhere. It is also important that a few thousands of play is present between end of shaft and brake pedal to insure full travel to operate internal check valve.


    Brian.

  13. #13
    cubunltd's Avatar
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    I bleed from the bottom up with a pressure pot ( Garden sprayer). However I always put the bleeder on the bottom of the caliper, thereby pushing all the air out to the top and into the master cylinder. Basically same setup as Steve Pierce's except bleeder at bottom. If you pump in from the top you trap air at the top of the caliper. Sometimes it works, sometimes not. Air wants to go up. Bleed once and I'm done.

    John

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