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Geo Disks With Stock Single Master Cyl

Discussion in 'Early CJ5 and CJ6 Tech' started by Jrobz23, Jun 1, 2019.

  1. Jun 2, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    Timgr, your explanation for a dual master is exactly how I THOUGHT they worked (you can lose line pressure in one circuit and the other will carry you) but twice in the last few years it has proven not to be the case in reality (for me). Both were OEM dual masters on a 97 Jeep and 2000 Ram. I can tell you, one lost REAR wheel cyl/line crippled ALL braking ability. It was not a 50% reduction (though losing a rear should net far less than 50% reduction I would think), it was 100% loss in braking ability. Dead petal all the way to the floor.

    After those encounters, my mindset has flipped on dual masters - as you might imagine. I no longer see the reason to remove the stock style equipment, specially after my own dual install didn't result in OEM quality fitment (very likely my own fault).
     
  2. Jun 2, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I've had the pedal to the floor with a dual master cylinder too. This was in my '85 F250, drove to work that morning brakes fine, go to leave at night pedal to the floor. If half of the system previously failed I certainly didn't know it. Personally I think with a single m/c one is more likely to notice ahead of time if something is going wrong with the brakes.
     
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  3. Jun 2, 2019
    timgr

    timgr Jeepin' Nerd 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    Not my experience. On my J10, the dual MC worked exactly as expected. Rear brakes went away in the Home Depot parking lot, and I drove home on the fronts. Can't explain previous poster's failures, but I also can't explain how a single cylinder system would be any safer. My Golf also suffered a burst line (common for old cars here), when it was being inspected for a sticker. The tech stomped on the brakes and it burst. Again, I drove it home the few blocks on the remaining circuit. Worked as advertised.

    The last single cylinder cars I owned both failed, one repeatedly. My '66 Squareback master cylinder failed all at once, but I was able to drive across town to home using the hand brake to stop. Scary in retrospect, but I was very young. My '65 F100 went through a series of rebuilt master cylinders, until I bought a new EIS master for it and it never failed again. These rebuilt cylinders would slowly go spongey, though I never had one fail altogether.

    Single circuit systems fail too. Place your bets and take your chances.
     
    Last edited: Jun 2, 2019
  4. Jun 2, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    Mine either Tim, to the floor but after pumping up the pedal I had brakes again.

    So was i but for me it was scary at the time. :shock:
     
  5. Jun 2, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    Def not saying the single is safer. I’m just saying that if I’m gonna lose all my brakes on a line failure, I might as well have stock parts and fitment.
     
  6. Jun 2, 2019
    45es

    45es Member 2019 Sponsor

    Naches, WA
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    Again your description is not correct. If the differential pressure valve were to function as you describe, once the spool moved and blocked either circuit closed, your master cylinder would stop functioning. The master cylinder would be hydraulically bound up. This condition would be the same as if a plug were installed into one half of the master cylinder circuits. Brake fluid does not compress.

    A good explanation of this can be found here: Proportioning Valves 101 - FORDification.com
     
  7. Jun 2, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    Well the thing is you should not:shrug: You may have to pump the pedal a few times but you should not loose the brakes completely because of a loss in one circuit- that's the whole idea behind the dual system.
     
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  8. Jun 2, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    Should not, but 2 for 2 I did. You can’t pump a petal that sits on the floor.
     
  9. Jun 3, 2019
    GTS Dean

    GTS Dean New Member

    Texas
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    45es:
    I would have to say "it depends on the machining of the center spool and the body" as to whether the differential pressure switch merely illuminates a warning light, or if the machining allows the spool to physically block the lower pressure (lost fluid) side which caused the fault.

    In the excellent Ford website you found, the spool does not block continued flow. However, from careful analysis of the first cutaway you provided, I believe that it has a dual function. If it is forced by the front circuit to the rear, the spool slides over the prop. valve pin and does not allow the poppet to open at all. The front circuit continues to flow as normal. The reverse situation appears to be true as well.

    Since the MC piston has already suffered a fluid loss severe enough to actuate the spool, it would seem to me that there would not be enough left to hydraulic lock anything. When the brake system is working normally, it is always up against a hydraulic lock situation because of being a closed system. That certainly doesn't stop the brake system from working, does it?

    For our friend JRobz, it would behoove you to investigate whether the Summit parts are merely warning light setups, or have a hydraulic port block function as well.
     
    Last edited: Jun 3, 2019
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  10. Jun 3, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    Will do. TY
     
  11. Jun 3, 2019
    45es

    45es Member 2019 Sponsor

    Naches, WA
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    Dean it's time to except the fact that your beliefs are wrong.

    You are correct that it would depend on the machining of the spool. If you read the article, it addresses the belief such as your as to why the spool does not block the incoming port of the differential pressure switch and is machined accordingly to allow fluid to pass.

    You keep saying , "I believe". Rather than to continue to guess, show us documentation that supports your opinion. I provided a well written document. Lets see yours.

    Possibly but I can tell you this, I for one am not willing to bet my life on it or anyone else's.

    Not true. The system is closed loop. Due to the fact the brake shoes and/or pads move when fluid is pumped into their respective cylinders, the master cylinder is not hydraulically bound. If you place a solid blockage into either one or both of the master cylinder passages preventing fluid movement, the master cylinder will be bound.
     
  12. Jun 3, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    OK.. we can move past the safety valve here. That is a nice to have, not a need to have.

    I would have a proper functioning hand brake for any oh-crap scenario.
     
  13. Jun 3, 2019
    GTS Dean

    GTS Dean New Member

    Texas
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    Duty Calls.JPG

    LOL - Let's just call a truce, OK?
     
  14. Jun 3, 2019
    45es

    45es Member 2019 Sponsor

    Naches, WA
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    Makes sense to me.
     

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