Brake bleeding.....

Discussion in 'Hangar Flying' started by MadProfessor8138, Dec 30, 2019.

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  1. Dec 30, 2019 #1

    MadProfessor8138

    MadProfessor8138

    MadProfessor8138

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    I wasn't quite sure which section to post this question to because of topic and aircraft so my apologies if it doesn't belong here.

    So the topic for today is bleeding brakes and why I cant seem to do it on a 1978 Piper Tomahawk.
    This brake system is driving me crazy and I can't figure out what I'm doing wrong.
    The problem started with just the right brake on pilots side and is now the entire system left & right - pilot & passenger side.....due to me,I'll explain.
    I've checked for leaks and cannot find any..

    1st attempt at bleeding right side,left side is good at this point :
    1.Hooked a pressure bleeder to right caliper and opened the bleeder valve.
    2. Applied pressure to system
    3. Pumped both right toe brakes....no pressure in cylinders
    4. Noticed reservoir on firewall was overflowing.
    5. Stopped bleeding

    2nd attempt at bleeding right side,left still good at this point.
    1. Ran tubing from right caliper to resevoir on firewall
    2. Cracked bleeder and let it gravity bleed for a few minutes,fluid was flowing and then stopped
    3. Pumped both right pedals to try to get fluid flowing again
    4. Got fluid flowing and pedal felt great then a big purge of air would come out and pedal would go to mush again
    5. Pumped more and fluid was flowing and it seemed all the air was out but couldnt get a firm pedal
    6. Stopped pumping right pedals and decided to pump parking brake
    7. Pumped parking brake and could get any pressure
    8. Now left brake is mush when it was rock hard.
    9. Quit for the day

    3rd attempt at bleeding,all pedals and emergency brake are mush................this is the recommended method in the Piper manual :
    1. Ran lines from both calipers to resevoir on firewall
    2. Pumped parking brake 50 times and locked it
    3. Cracked right bleeder
    4. Pumped both right pedals and fluid flowed
    5. While pumping the pedals would firm up and purge a big shot of air and then turn to mush again
    6. Shut down right side and did the same procedure to the left side
    7. Shut left bleeder off
    8. Pumped parking brake 25 times
    9. Bled right and left calipers again
    10. Pedals & parking brake are mush
    11. Quit for the night

    4th attempt to bleed,all pedals and parking brake are mush :
    1. Tubing on both calipers running to resevoir on firewall
    2. Pumped both right pedals while someone cracked right bleeder and shut bleeder down for me to pump it up again
    3. Started getting good pedal and then would purge a shot of air and pedals would go to mush again
    4. Bled both sides the same way and couldn't get a good pedal
    5. Stopped for the day

    Soooo......I've tried :
    1.From caliper up with pressure
    2. Gravity bleeding by pumping the pedals
    3. Gravity bleeding per Piper with the emergency brake in use
    4. Gravity bleeding with pedals and someone working the bleeders

    The pedals are mush and will only firm up before spitting out a shot of air !!!!
    What am I doing wrong ???
    I've had brake systems be difficult but this is pure madness.....

    I went and bought a suction bleeder in hopes that my 5th attempt will work out better.
    The suction bleeder will pull fluid from the reservoir to the caliper.....

    Kevin
     
    Last edited: Dec 30, 2019
  2. Dec 30, 2019 #2

    TFF

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    I know Cherokees are hard to bleed because the brake line has a high spot in the wing that can hold a bubble. I don’t know if that happens with a Tomahawk. I would bleed up from calipers. I would be ready to suck out the reservoir. Pump up, close off the bleed screw, suck out, repeat a couple of more times. Any time you stop pumping, close the bleed screw. Keep doing it the same way. If it takes ten times, it takes ten times.
     
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  3. Dec 30, 2019 #3

    MadProfessor8138

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    I'm not going to lie....I'm confused about the way this system is acting....

    Why is the pedal getting hard right before it purges a shot of air and then goes to mush with nothing but fluid in the line ?

    Why did it pump 1/4 gallon of fluid through the system up to the reservoir and still couldnt get a firm pedal ?

    Why isn't this thing bleeding properly while following the Piper procedure ?

    Sorry......I'm just agitated about missing 2 perfect weekends of flying while dealing with this issue.

    Kevin
     
  4. Dec 30, 2019 #4

    Aerowerx

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    Clogged line????
     
  5. Dec 30, 2019 #5

    TerryM76

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    Hey Kevin.

    We have a 79 model at our A&P school and it's a challenge at times to get the brake system bled.

    I have not used pressure bleeding procedure as defined in the Piper maintenance manual. Using only the gravity method will result in proper bleeding. Let's see if I remember this correctly. Starting with the emergency brake system, have a helper open the bleeder screw on a caliper and pump the handle to establish a fluid flow. Have helper close the bleed screw when he sees fluid streaming out. Pump the handle and build up pressure and hold handle toward locked position while helper opens bleed screw and releases air & fluid and then close screw. Keep repeating until a good air-free flow of fluid is established when opening the screw and repeat process using caliper on opposite main wheel. Emergency brake should feel firm.

    I don't recall it being a necessity to lock emergency brake handle while doing the mains and I only go back and check it after bleeding cylinders at the pedals. As for the pedals, pick a side and start the process all over again by pumping a pedal to build pressure and hold, have the helper open the screw while keeping the pedal pressed. Helper should close the screw while pedal stays depressed. Again, just repeat until a firm pedal is established. Makes sure your helper checks the reservoir frequently or you're in for a long frustrating day.

    Hopefully this helped.

    Terry.
     
  6. Dec 30, 2019 #6

    TerryM76

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    Actually Piper refers to it as a "Hand/Parking" brake..... Not Emergency brake as I incorrectly called it.
     
  7. Dec 30, 2019 #7

    mcrae0104

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    Sorry I can't help with your problem.

    But... you may want to check and see if bleeding brakes is on the owner maintenance list in the FARs and that you hold the appropriate certificate (i.e. private pilot) so that you can make the log entry. I would hate to see you get in any trouble over it. I only mention it since you were asking about studying for your knowledge test recently. :)
     
    Last edited: Dec 30, 2019
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  8. Dec 30, 2019 #8

    TerryM76

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    Good suggestion. It's not listed as a Preventive Maintenance item in Appendix A to Part 43. Get an A&P to supervise and sign off your work.
     
  9. Dec 30, 2019 #9

    bmcj

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    If I were having this problem, I would follow this easy two step process:

    1. Look over my should to make sure Alan Funt isn’t there, then...

    2. Ask the folks here at HBA.
     
  10. Dec 30, 2019 #10

    MadProfessor8138

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    TerryM76...I referred to it as the "emergency" brake in my original post,my mistake.......wasn't paying attention when I wrote it due to thinking about everything that I had done so far and didn't want to leave anything out while typing.
    I edited the original post to "parking" brake.
    Sorry for that oversight.....

    Aerowerx......nope,not a clogged line,fluid is passing with no problem....just can't seem to get all of the air out.

    mcrae0104....I'm not too worried about the legality of the situation,our A&P oversees all of the work and takes care of the legal stuff.
    There are certain issues that I step back and watch him work but this isn't one of those times.

    bmcj.......you left out step 3,which is kicking and cussing a bit when the 2 methods Piper published to fix the situation don't.
    At this point I feel more like I'm on an episode of Punked rather than Candid Camera.

    Kevin
     
  11. Dec 30, 2019 #11

    MadProfessor8138

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    TerryM76........the parking brake is one of the issues that I'm having.
    I can't seem to get any pressure by pumping it and instead of pushing air & fluid away from the caliper when pumped it will actually pull fluid back into the caliper if I pump it or even lock it in the applied position.
    This part has me confused because it should be pushing fluid out of the caliper when applied just like the cylinders on the pedals.

    Theoretically,you should be able to pump the parking brake to circulate fluid through the whole system and not have to pump the toe brakes to bleed those cylinders individually.....the parking brake "should" flush them....in theory.

    Am I not understanding something pertaining to the parking brakes operation.....?

    Kevin
     
    Last edited: Dec 30, 2019
  12. Dec 30, 2019 #12

    plncraze

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    The parking brake is a pain. One of the guys I used to work with used to pump it a few times while bleeding to try to get fluid into it. It does take awhile.
     
  13. Dec 30, 2019 #13

    Dana

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    Might be a bad seal on one of the pedals or the parking brake letting air in.
     
  14. Dec 30, 2019 #14

    MadProfessor8138

    MadProfessor8138

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    Talked to an I/A down in South Carolina who has worked on quite a few Tomahawks.....
    He recommendee that I crack the line at the parking brake and purge the air that way.
    He said that fluid will just bypass that section if it's full of air and force it out the resevoir.
    So.......as soon as I can get the plane into the main heated hanger I'll go that route.

    Kevin
     
  15. Dec 30, 2019 #15

    TerryM76

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    It does sound like air is trapped and the maintenance manual tells you how to bleed air out of the system when components are removed or lines disconnected. Keep us posted.
     
  16. Dec 30, 2019 #16

    MadProfessor8138

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    Admittedly,I messed up when I tried to bleed the system following the procedure in the service manual.
    I had a solid left pedal but needed to bleed the right side.
    When I pulled the parking brake,per the Piper manual,I transferred air into the left side.
    Now both sides need to be bled.
    When there is room in the main heated hanger and I can get my plane in I will attempt to bleed the system starting at the parking brake.
    The thought of being soaked in hydraulic fluid in an unheated hanger isnt very appealing to me right now.
    So,at this point it's....hurry up and wait.

    Kevin
     
  17. Dec 31, 2019 #17

    Dan Thomas

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    Pipers are a royal pain to bleed. To make it worse, they used way too much rubber hose in the system so that the brakes are spongy even when the air is all out.

    And the wing dihedral creates a high spot in each wing where air will accumulate in the lines, and the sonly way to move that out is through pressure bleeding from the caliper up. The fluid needs to be moving quickly to carry the air along and out. Pumping the brakes up just compresses that long bubble, and openeing the bleed screw just lets it expand again and it forces fluid out without moving along itself. If it does move some, it just moves back up to its high spot when the brake is released.

    Read the maintenance manual very closely. Piper knew their system was a pain. They give detailed instructions on bleeding.

    You'll go through a lot of fluid and you'll get really oily. Then you'll go buy a Cessna, which is a delight to bleed. Takes ten minutes max. No muss.
     
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  18. Dec 31, 2019 #18

    Pops

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    My Cherokee was a pain in getting all of the air out of the system. Takes a lot of work to get the air out of the hand brake.
     
    Last edited: Dec 31, 2019
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  19. Dec 31, 2019 #19

    MadProfessor8138

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    Dan Thomas.......I've followed both bleeding procedures,gravity & pressire,outlined in the Piper service manual.
    Neither procedure has removed all of the air from the system....I'm still getting air trapped in the parking brake.
    The I/A that I spoke with today has worked on Tomahawks for years and says the procedure Piper outlined will not work most of the time.
    Before I could tell him what my system was doing he described to me what problem I was experiencing,so I'm going to give him credit by saying that he knows what I should do to remedy the situation because he knew what problem I have before I even told him.
    His advice to crack the line at the parking brake makes since because that seems to be where the air is trapped.
    I'm pretty sure that will fix the problem.
    I'm just waiting for the main heated hanger to be available before I get soaked with hydraulic fluid.

    Kevin
     
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  20. Jan 20, 2020 #20

    MadProfessor8138

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    Just thought I would give everyone an update on the Tomahawk brake situation.

    Saturday :
    The main "heated" hangar was finally available.....yay.
    The bleeder screws on both calipers were getting to the point that they were a little rounded so I went in search of new parts.
    Nobody had individual bleeders so I ended up buying a package with assorted bleeder sizes for $12.50.
    Bleeders were teflon taped and installed...no problem.
    I also picked up a vacuum bleeder from Harbor Freight for $32.
    Using the vacuum bleeder I attempted to bleed the system from the top down....no joy !
    Then I came up with the bright idea that if the vacuum bleeder could suck fluid in by creating a vacuum it should be able to push fluid out by plugging the exhaust and pressurizing the container.
    So.......with exhaust plugged and container full of fluid I pressurized it with air......now I'm bleeding from the bottom up.
    Still took a while but with help from the guys pumping the master cylinders and working the bleeders while I worked the container......the brakes are done !!!
    That was a b**ch to get all of the air out of the system,there was a ton of it and the routing of the lines doesn't help !!!

    Sunday :
    I wasn't too keen on climbing in the seat and stepping on the brakes knowing my track record with the failed attempts up to this point so my brake pumper volunteered for the job.
    He jumped in,stepped on each brake and even pulled the parking brake......he reported they were all still solid and felt good.
    I'm glad it's over..........

    Air,air and more air....... !!!
    20200118_144513.jpg

    Here's my brake pumper.....Ed.
    All around awesome guy......
    20200118_144518.jpg

    And here is the airport owner / A&P / bleeder man.....Dennie
    When asked if he had fun with my brakes his reply was..."reply edited for sensitive readers".....lol.
    That seems to be his usual reply when it comes to anything pertaining to my Tomahawk....
    20200118_144521.jpg

    All joking aside.....I'm glad the brakes are fixed and I'm very fortunate to be associated with some great guys at the airport....everyone should be so lucky.

    Kevin
     
    Last edited: Jan 20, 2020
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