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  • Spongy pedal

    I have recently converted to disc brakes in the front using 78 granada spindles. The master cylinder is new and from a granada as well and I have an adjustable proportioning valve currently. New 3/16 lines have been installed front and rear with the rear drums being rebuilt as well. After bleeding them several times the pedal is still very soft and the brakes dont seem to "grip" enough as a guy can still turn the wheels even if the pedal is right to the floor. Any thoughts?

  • #2
    What booster are you using? If it's the factory booster then that is your problem. The factory booster is just barely adequate for drum brakes. It was not designed for the pressures needed to handle disc brakes.

    John
    John Pizzi - Squarebirds Administrator

    Thunderbird Registry #36223
    jopizz@squarebirds.org 856-779-9695

    https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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    • #3
      I am using a 7inch dual diaphram booster

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      • #4
        What booster are you using that fits a Granada master cylinder? Give us details on exactly what parts you are using. A spongy pedal is most always a leaking booster or air in the system.

        John
        John Pizzi - Squarebirds Administrator

        Thunderbird Registry #36223
        jopizz@squarebirds.org 856-779-9695

        https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

        Comment


        • #5
          I agree with John and that is where you should start. Most people don't encounter a 'dry' master cylinder or the required setup between the master and booster. It's already been done at the factory. But, when you CHANGE components, the setup needs to be done again (including bench bleeding).

          There is another issue that can cause a spongy pedal... firewall bracket flexing. All the mechanical components need to be solidly mounted. Put someone under the hood, watching the booster/master setup while a helper stands on the brake pedal. If he sees any flexing at all, that will cause a spongy pedal.

          I have tried the dual diaphram 7" booster. It's 'ok' but I like the 8" dual diaphram booster even better.
          Brake pads and shoes stop far better after they are 'bedded-in' so expect improvement in stopping distance in the coming months. - Dave
          My latest project:
          CLICK HERE to see my custom hydraulic roller 390 FE build.

          "We've got to pause and ask ourselves: How much clean air do we need?"
          --Lee Iacocca

          From: Royal Oak, Michigan

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