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Brake Help

Discussion in 'Early CJ5 and CJ6 Tech' started by Jonbbrew, Jul 19, 2021.

  1. Jul 19, 2021
    Jonbbrew

    Jonbbrew Member

    Paso Robles, CA
    Joined:
    Mar 14, 2015
    Messages:
    739
    Hello all,

    I know it’s not really about early CJ5 except for that it’s on mine.

    the PO put in an early 80’s import brake booster with 11” drum upgrades. I rebuilt all brakes, and master cylinder and replaced the brake booster with a rebuild from Cardone.

    I’m trying to get it all bled etc abs noticed that the engine RPMs change when I press on pedal. I assume it has something to do with the vacuum but what?
     
  2. Jul 19, 2021
    Rich M.

    Rich M. Shoe salesman 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Maryland
    Joined:
    Mar 23, 2008
    Messages:
    2,169
    Rpm goes up or down? Leaky boosters are a vacuum leak.
     
  3. Jul 19, 2021
    Jonbbrew

    Jonbbrew Member

    Paso Robles, CA
    Joined:
    Mar 14, 2015
    Messages:
    739
    Up so since it’s a brand new rebuilt I guess it is a vacuum leak on hose?
     
    Last edited: Jul 24, 2021
  4. Jul 19, 2021
    Rich M.

    Rich M. Shoe salesman 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Maryland
    Joined:
    Mar 23, 2008
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    2,169
    Yep you got a leak somewhere. Just because its newly rebuilt doesnt mean anything anymore. The diaphragm could be bad, nicked on install etc. If it's a flaps piece just return / swap it.
     
  5. Jul 19, 2021
    Jonbbrew

    Jonbbrew Member

    Paso Robles, CA
    Joined:
    Mar 14, 2015
    Messages:
    739
    So that means when I push on the pedal it’s pushing air into the manifold this increasing RPM?
     
  6. Jul 19, 2021
    PeteL

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

    Hills of NH
    Joined:
    Aug 3, 2003
    Messages:
    9,754
    More like allowing the manifold to suck in excess air, for as long as the leaky booster is activated by the pedal.
     
    Fireball likes this.
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