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Weird Brake Issue

Discussion in 'Early CJ5 and CJ6 Tech' started by Southtowns27, Oct 3, 2016.

  1. Oct 3, 2016
    Southtowns27

    Southtowns27 Custom Title

    The Backhills of...
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    I'm having a weird brake issue with my Jeep. It has 11" Ford Bronco brakes on all 4 corners and has Herm's dual master cylinder conversion. The issues started after I removed the rear axle to rebuild it. After reinstallation, I can't get my brake pedal back to normal height. It stops an inch from the floor and doesn't stop very well. It does not feel spongy. Presumably only half of the brakes are working, they're split front/rear, but I can't tell which is working and which is not. I have bled the brakes about 9000 times, checked the adjustment, changed the brake hoses, and tried another master cylinder, all with the same result. What am I missing?!?!?! It's driving me completely nuts. I'm not sure how the master cylinder is put together, but do I need to bleed the fronts first or something to get enough stroke to properly bleed out the rear? Even though I never had the fronts open? Thoughts??
     
  2. Oct 4, 2016
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    How old is the master cylinder? Did it run dry when you had the rear axle out? May just need a good bench bleed then lines installed and re-bleed the system.
     
  3. Oct 5, 2016
    Southtowns27

    Southtowns27 Custom Title

    The Backhills of...
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    The M/C is about 3 years old. It didn't run dry when the axle was out. I tried a second brand new master cylinder and got the same results
     
  4. Oct 5, 2016
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    Did you disassemble the drum brake components when you had the rear axle out, or just remove the whole axle as a complete unit leaving the brakes in tact?

    What does the pedal feel like when it stops an inch from the floor? Is it a thud like it is hitting something? Or does it just lose steam? If you have your foot fully pushed down and slip it off the pedal, does the pedal slam up or slowly return to its home?

    If you pull up on the pedal, does it stay up, or limply drop back down to an inch from the floor?

    Have you lubed the pivot barrel at the frame to rule out friction at the point? That sounds too simple, but that could be the culprit.
     
  5. Oct 5, 2016
    PGHCJ5

    PGHCJ5 I smell something broken...

    'yinzertahn
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    Could you please elaborate about the pivot barrel? I have an intermediate with hanging pedals so it may not apply. Just curious. Thanks in advance....
     
  6. Oct 5, 2016
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    Whatever you call it. :)
    The tubing that the early clutch and brake pedals pivot on. The tubing with the cotter pin in the bottom of this pic.

    [​IMG]
     
  7. Oct 5, 2016
    PGHCJ5

    PGHCJ5 I smell something broken...

    'yinzertahn
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    Thanks! Appreciate the clarification and image. That is certainly different than my setup. I'm not too familiar with the early's enough. Learn something new everyday!

    BTW - you have quite an Epic thread in the "Introductions" section. I read the whole thing.
     
    ITLKSEZ likes this.
  8. Oct 6, 2016
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Normally referred to as a bellcrank;)
     
  9. Oct 6, 2016
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I thought this is the bellcrank?
    [​IMG]
    I'm talking about the pivot point for the pedals themselves.
     
  10. Oct 6, 2016
    Southtowns27

    Southtowns27 Custom Title

    The Backhills of...
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    I did have the brakes disassembled. I have checked and double checked the adjustment to be sure they aren't too loose. At one point they were actually adjusted too tight (dragging) and I still had a ton of pedal travel. When the pedal finally stops, it feels firm, not spongy. If I slip my foot off the pedal while it's depressed, it returns to the top as normal. I have also adjusted the master cylinder push rod to get rid of all the free travel. As soon as the pedal moves, it's moving the piston in the M/C. Pivot barrel is well greased.
     
  11. Oct 6, 2016
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Gotcha. The part one pedal attaches to and the other pivots on is called a brake pedal shaft according to my Factory Service Manual.
     
  12. Oct 7, 2016
    jeepstar

    jeepstar Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Sheboygan
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    The brake pedal shaft according to the FSM, but Bell crank according to the rest of the world
     
  13. Oct 8, 2016
    Jomani

    Jomani New Member

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    image.gif View attachment 35040
    [QUOTE="Southtowns27, post: 1301441, member: 1092] Presumably only half of the brakes are working, they're split front/rear, but I can't tell which is working and which is not.[/QUOTE]

    When you say that only half the brakes are working, I am not sure that you fully understand the operation of a dual master cylinder. The image above shows a fairly good representation. If you crack both brake lines at the master cylinder, the pedal should drop to the floor. If you crack only one, the pedal will drop significantly farther than normal but the opposite cylinder will still build/hold pressure. The spring in the front (circuit 1) is lighter than the rear spring (circuit 2). When the pressure in circuit 1 overcomes the spring pressure in circuit 2, pressure starts to build in circuit 2. The springs inside the master cylinder allow each circuit to operate somewhat independently of each other. Pedal height is not so much factor of the hydraulic system as it is the mechanical return mechanism (the return springs). Pedal travel would indicate a hydraulic problem. If all of the pedal mechanics are operating freely then I would start looking for air in the system.

    Start from the master cylinder and work your way to the back - crack the line and have someone gently push on the brakes. You should get a nice stream of fluid with no bubbles. You may need to tighten the connection, pump the brakes a couple of times and crack again until you get a steady stream. If you have a proportioning valve in the system, you need to make sure that it is not stuck.

    If the hydraulic portion of the system is intact and air and leak free, the problem is most likely somewhere in the pedal/master cylinder area.
     
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