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Duo-servo Brakes?

Discussion in 'Early CJ5 and CJ6 Tech' started by earlycj5rocks, Jan 31, 2017.

  1. Jan 31, 2017
    earlycj5rocks

    earlycj5rocks New Member

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    How can I tell whether these are duo-servo brakes on my 1960 CJ6? I'm trying to figure out if the short shoe should face front or back. wheel1.jpg wheel2.jpg
     
    earlycj5rocks, Jan 31, 2017
    #1
  2. Jan 31, 2017
    ronnie victor

    ronnie victor Member

    raleigh, nc
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    I believe that the larger surface area shoes always face frontwards, for any vehicle with shoe brakes.
     
    ronnie victor, Jan 31, 2017
    #2
  3. Jan 31, 2017
    Twin2

    Twin2 not him 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Virginia Beach, VA
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    long shoe to rear on all 4 corners
     
    Twin2, Jan 31, 2017
    #3
  4. Jan 31, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Actually it's the short shoe that goes in the front, but there has been debate on the 9" brakes about the short shoe.
     
    Glenn, Jan 31, 2017
    #4
  5. Jan 31, 2017
    eti engineer

    eti engineer Member

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    The short one in the front, always. Just did mine and they work great, but the vacuum assist I installed sure helps to stop the 31's better.
     
    eti engineer, Jan 31, 2017
    #5
  6. Jan 31, 2017
    eti engineer

    eti engineer Member

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    Glenn, what was the question? I am interested...
     
    eti engineer, Jan 31, 2017
    #6
  7. Jan 31, 2017
    ETZFAM

    ETZFAM FLATIES & ROUND FENDERS, SOME EVEN RUN

    WENATCHEE, WA
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    Smaller brake shoe pad always goes forward.
     
    ETZFAM, Jan 31, 2017
    #7
  8. Jan 31, 2017
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    For 9" brakes per the military manual-


    upload_2017-1-31_10-39-37.png
    upload_2017-1-31_10-42-9.png

    H.
     
    Howard Eisenhauer, Jan 31, 2017
    #8
  9. Jan 31, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    As I understand it the issue is the way the 2 brake shoe systems work. Since the shoes act independently on the 9" brakes it seems the short shoe is better in the rear (at least according to the military).
     
    Glenn, Jan 31, 2017
    #9
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  10. Jan 31, 2017
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    To elaborate on the 9" brakes there's no floating star wheel adjuster as there is with most drum brakes people are familiar with, there's a fixed pivot pin .

    Brakes with the floating adjuster allow the shoes to move together, with the fixed pivot they operate more independently.

    With the floating adjuster the front shoe grabs & apples force the the rear shoe increasing the effective braking power. With the longer shoe in front the brakes may become so energized they don't release when pressure is removed from the wheel cylinder.

    I'm not really sure on the rational for having a short shoe in the 9" units, to me it seems they would work better with two long ones..

    H.
     
    Howard Eisenhauer, Jan 31, 2017
    #10
  11. Jan 31, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I agree, it sure seems that way.
     
    Glenn, Jan 31, 2017
    #11
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  12. Jan 31, 2017
    Daryl

    Daryl Sponsor

    Bonney Lake, WA
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    9" brakes the short shoe goes to the REAR.
     
    Daryl, Jan 31, 2017
    #12
  13. Jan 31, 2017
    ronnie victor

    ronnie victor Member

    raleigh, nc
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    In checking my FSM for my '66 CJ5, I see a data table for 9" brakes listing the larger (surface) area is to be forward (direction of driving) for all wheels.

    Surface areas:

    10.2 x 1.75" front shoe
    6.6 x 1.75" rear shoe
     
    ronnie victor, Jan 31, 2017
    #13
  14. Feb 1, 2017
    3b a runnin

    3b a runnin Active Member 2023 Sponsor 2022 Sponsor

    virginia
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    With 9" brakes, just letting off the gas is the best brakes you've got.:n:
     
    3b a runnin, Feb 1, 2017
    #14
    ITLKSEZ, dozerjim, cadwelder and 1 other person like this.
  15. Feb 5, 2017
    earlycj5rocks

    earlycj5rocks New Member

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    Check this out guys.
     

    Attached Files:

    earlycj5rocks, Feb 5, 2017
    #15
  16. Feb 5, 2017
    eti engineer

    eti engineer Member

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    2-27-16 cockpit view.JPG

    new MC installed.png

    That's why I added hanging pedals, a vacuum booster and a dual reservoir master cylinder. My brakes work great now, even with 31" tires. Pedal pressure is really light and I can actually lock them up. But I do agree, even with 4:27 gearing instead of the 5:38 gears, letting off the gas slows down the Jeep tremendously.
     
    Last edited: Feb 5, 2017
    eti engineer, Feb 5, 2017
    #16
  17. Feb 6, 2017
    PeteL

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

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    That is the One True Way as I have always heard it.
    Brake shoes tend to be self-energizing with the direction of rotation towards an anchored (pivot) end. Therefore the short lining goes there. The trailing shoe needs the longer lining in order to act equally.
     
    Last edited: Feb 6, 2017
    PeteL, Feb 6, 2017
    #17
  18. Feb 6, 2017
    wheelie

    wheelie beeg dummy 2024 Sponsor 2023 Sponsor

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    What manual is this from? Interesting and handy.
     
    wheelie, Feb 6, 2017
    #18
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