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Mc Bypassing? Near Miss

Discussion in 'Early CJ5 and CJ6 Tech' started by CJ Joe, Oct 4, 2021.

  1. Oct 4, 2021
    CJ Joe

    CJ Joe Truckhaven Tough!

    Pinon Hills, CA
    Joined:
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    Had a hairy road experience on Saturday. I was driving the jeep for a few local errands into town. On the way back, doing about 63 on a slight down grade on a two-lane desert highway I approach a signaled intersection. Just about at the stop or go point the light turns yellow and I step on the brakes. Pedal goes all the way to the floor with zero resistance and not even a hint of slowing. By now I'm almost at the panic stop range of the intersection. Don't know why I didn’t pump, but I didn't. Downshifting like a madman, chirping the rear tires, at what must have been about 15 MPH I grabbed the parking brake and pulled real hard. Stopped a few feet into the intersection realizing I had just missed what could have been a horrible experience.

    For the back story. With added weight and larger tires the brakes were inadequate. A couple of years ago I converted to power disc/drum, hanging pedals and hydro clutch. Those 11” rear drums with parking brakes each side and lever handle between the seats saved my butt this weekend. Life’s priorities got in the way and the jeep sat. An occasional run around the block exhibited a soft pedal now and them. A mechanic friend drove it and said the master cylinder was bypassing. After I moved I ordered another MC and installed it. Same issue. So now I’m wondering what it could be. A second new/reman MC is bad or is it something else? What could mimic a bypass?
     
  2. Oct 4, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Post Falls, ID
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    If there is no fluid leaking out anywhere, a leaky MC can really be the only culprit. New parts aren’t guaranteed to be good parts. Glad you’re ok.

    If it’s the single circuit system, it might be a good time to upgrade. If it’s a double circuit, something is definitely faulty to go flat to the floor with zero braking.
     
    sterlclan likes this.
  3. Oct 4, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    That kind of thing was more or less normal when I was young. Why we called them "emergency" brakes - not "parking brake." (Harumph...)

    Will the pedal "come up" with rapid pumping? If so, it may be air in the system, or a maladjustment at one or more wheels. Lost pad at one caliper, or a stuck wheel cylinder suddenly released, or...

    The m/c should have a double set of seals and also might pump up if just one is leaking.
     
    Last edited: Oct 4, 2021
  4. Oct 4, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    You didn't mention if you bled the brakes after installing the replacement master cylinder?
     
  5. Oct 4, 2021
    montanacj

    montanacj Member

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    Sounds scary. I lost steering in an older k5 blazer on the highway and ended up heading into oncoming traffic. Luckily it was an emergency search and rescue vehicle and I had lights on but the minivan I almost hit as I went into the ditch on opposite side of highway was to close for comfort
     
  6. Oct 4, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Since you say that it sat it seems that you didn't drive the Jeep very much after doing the original brake work? Maybe it still had air in the system after the original brake work?
     
  7. Oct 4, 2021
    Dave Deyton

    Dave Deyton Member

    Fuquay-Varina, NC
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    I remember on the 66 Wagoneer, my dad going through a stop light like a dream. Holding down the horn wide open with no slowing down and the pedal to the floor. I was about 12. Fortunately, everyone stopped as we flew through the intersection.

    I tell my son he doesn't know how good he has it with the new brakes. I always leave more room to stop than he does, because I have been in older vehicles with brake failure.

    11in brakes will be going on the 64 CJ5, and I will look at doing the dual MC also.

    Glad you got it stopped safely.




    Dave
     
  8. Oct 4, 2021
    CJ Joe

    CJ Joe Truckhaven Tough!

    Pinon Hills, CA
    Joined:
    Nov 9, 2002
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    It is a dual circuit system. 1" bore Corvette style MC w/ 8" booster. The MC (both times) was bench bled and installed. Put a level on it and made sure every last bubble burped out the compensation ports then bled all four corners. I have speed bleeders and usually go well beyond what appears good.

    The booster works so well there is no effort. To the point I have considered plugging the vacuum and give it a try. With engine off pedal is rock hard and no sinking over time. When running the lack of braking effort bothers me, but it's still a firm pedal. I like some feel. While not using it I have made a point of "driving around the block" monthly to keep things lubricated. That is when I first noticed the problem on a rare occasion and it prompted me to change the MC, but it continues.

    It will stop the jeep on pavement so quickly it feels like it'll rip the axles off. It's just that 1 in a 1000 that it doesn't and that's 1 time too many.

    I'll likely bleed it again just to eliminate that possibility (I've screwed stuff up before). I still have the first MC and just may buy a kit for it and swap them out. I know how questionable parts quality can be these days, but gotta have good brakes.
     
  9. Oct 4, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Post Falls, ID
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    Just curious… Have you mysteriously lost brake fluid? I.e., have you checked your fluid level since this happened?

    A leaky booster can suck fluid into the canister through the plunger, and you’ll lose fluid without realizing it because there’ll be no puddles.
     
    jeep peep69 likes this.
  10. Oct 4, 2021
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    Two independant braking systems are a mandatory requirement- have been for a long long time. Now we have redundant hydraulic systems but back in single circuit days the parking brake fulfilled the requirement & yeah when I was growing up they were called "emergency" brakes.
     
  11. Oct 4, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    I still have the ingrained habit of lightly pumping the pedal, "just to check", as I get off the highway or approach a stop sign.
     
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  12. Oct 4, 2021
    dozerjim

    dozerjim Member 2021 Sponsor 2020 Sponsor

    western New York
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    x2
     
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  13. Oct 5, 2021
    amboynut

    amboynut Member

    Chelatchie, WA
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    That's where my money is.
     
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  14. Oct 9, 2021
    CJ Joe

    CJ Joe Truckhaven Tough!

    Pinon Hills, CA
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    Fluid level is normal and I probed the booster and it is dry.

    What I don't understand is if there is air in the system the characteristics would be consistent and not intermittent as I'm experiencing, right?
     
  15. Oct 9, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Post Falls, ID
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    Yes, unless you have a brake line that is too close to an exhaust component. That section of fluid inside the line will boil and create a vapor pocket. It will force some fluid to the path of least resistance (back into the reservoir), and the next time you hit the brakes, you’ll be compressing that air bubble rather than applying brakes. Check to make sure your clearances around the exhaust are adequate.
     
  16. Oct 9, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    Intermittant failure has been my experience when a m/c seal is failing.
     
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  17. Oct 9, 2021
    Alan28

    Alan28 Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Châtillon en...
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    Tha
    That's your destiny, man :D
     
  18. Oct 9, 2021
    Alan28

    Alan28 Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    It happened to me with, long ago, with a Norton "model sport" ... A good way to test one's luck.
     
  19. Oct 9, 2021
    Rich M.

    Rich M. Shoe salesman

    Maryland
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    Two things come to mind. Ime front calipers need pulled off, a block of wood inserted and the bleeders pointed straight up. You can bleed them multiple times on the bracket, get straight fluid and still have air. Second the reproduction fixed proportioning valves are notorious poor parts and leak.
     
  20. Oct 9, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    How about pumping the brakes a few times and then wedging a 2x4 between the seat and the brake pedal and let it sit for a while then check to see if it's still firmly wedged in.
     
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