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Intermittent Brakes

Discussion in 'Early CJ5 and CJ6 Tech' started by Buildflycrash, Sep 21, 2020.

  1. Sep 21, 2020
    Buildflycrash

    Buildflycrash More or Less in Line. 2024 Sponsor 2022 Sponsor

    Gulf Breeze FL...
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    Brakes had been perfect for the first year I drove the Jeep. I do have a slow leak at the proportioning valve where the rears connect. I’ve let the fluid get low a couple times but a refill and bleeding always solve the problem. Recently on trail rides the brakes occasionally go to the floor! I can pump them a couple times and then be fine for 30 minutes then all the sudden almost nothing. I’ve bled them thoroughly a couple times and they stop really well except when they don’t.

    Dual MC under floor
    Dana 30 disc front
    Dana 44w 12” brake in rear.
    rubber hoses in great condition -18 months old.

    What do y’all think?
     
  2. Sep 21, 2020
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    12” brakes on the rear 44? I have to question that.
    If you have a leak out then you could be sucking air in causing your problem.
    Are the rear drum brakes adjusted correctly?
    Do you have residual pressure valves in the system?
     
  3. Sep 22, 2020
    Buildflycrash

    Buildflycrash More or Less in Line. 2024 Sponsor 2022 Sponsor

    Gulf Breeze FL...
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    12” may be 11”? From 70s CJ
    I thought of sucking air but the leak is very small.
    I did adjust the rears very recently. Had the same issue before and after.
    No residual valve. Does have proportioning valve from XJ w/ disc front drum rear.
    The mystery is this same setup worked perfectly for a year + before the problem. And I haven’t changed anything.
     
  4. Sep 22, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Pullman, WA
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    Sounds a lot like a master cylinder going out. Check this to make sure your vent ports of properly open when the brakes aren't applied: Home | LBCC
     
  5. Sep 22, 2020
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    I’m trying to follow where you are going here. If the vent port was plugged the brakes would most likely self apply which should be quite noticeable. Your link to LBCC confirms that. Unless grossly overheated causing the moisture in the brake fluid to boil causing air/steam in the fluid to form the brakes won’t just suddenly go out.
     
  6. Sep 22, 2020
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Fix your known problem first. I.e. the leak. That is unsafe in any case and should not be driven, especially on the road or trail until fixed.
     
  7. Sep 22, 2020
    jeepstar

    jeepstar Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Sheboygan
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    if you have a leak in the brake line, i suggest fixing that before trying to figure out why you have brakes that are intermittent. sometimes its the obvious, and simple things that are in fact the cause of problems.
     
  8. Sep 22, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    This.
     
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  9. Sep 22, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Pullman, WA
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    If it's not adjusted right it can also cause premature wear of the master cylinder seals. I'm assuming he put a new master cylinder in when he did the work last year and that could be a reason it's gone bad so soon.

    Could also be a bad new parts or maybe he put in a used master cylinder and it's just worn out. Contaminated brake fluid can also damage the seals. Whatever the root cause is, the symptoms sound like a bad master cylinder.
     
  10. Sep 22, 2020
    Buildflycrash

    Buildflycrash More or Less in Line. 2024 Sponsor 2022 Sponsor

    Gulf Breeze FL...
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    MC replacement isn't really a good option right now. I've got one more wheeling trip planned for Oct and then it all comes out to install the swinging pedals and T18. Dieing in Brake failure accident doesn't seem like a good option either. :confused:

    Any other ideas?
     
  11. Sep 22, 2020
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    Carry an anchor?
     
  12. Sep 22, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Depending on what master cylinder you're using, rebuild kits are only on the order of $15.00. New seals and you should be good to go until you swap it out.
     
  13. Sep 22, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    dozerjim, 73 cj5 and ITLKSEZ like this.
  14. Sep 22, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I was thinking an air horn to warn others you can't stop.
     
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  15. Sep 22, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Or just make sure the person in front of you has good brakes.
     
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  16. Sep 22, 2020
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    ...and your insurance is paid up.
     
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  17. Sep 22, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    And hope the person you hit hasn't been on this forum. :D
     
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  18. Sep 22, 2020
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
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    Y’all are too much. :rofl:
     
  19. Sep 22, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Also with the dual master cylinder setup that is on this Jeep I'm not getting why this problem is occurring.
     
  20. Sep 22, 2020
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
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    The fluid could be bypassing a piston in the master cylinder.
     
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