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brake setup help

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  • brake setup help

    I've got an odd pedal feel and I'm looking for pointers.

    What I've got on the car:
    B13 booster
    S12 BMC
    braided stainless lines
    J30 front brakes
    stock rear brakes
    ****ty parts store pads front and rear, semi-metallic

    I'm not exactly sure if I have a problem or not but I'm not happy with the pedal feel. When driving the brakes have a small (maybe half-inch of travel) dead zone and then bite pretty good. The fronts will lock somewhat easily. When the car is off and the booster is not evacuated, instead of being totally stiff like normal it's more like: take up pedal slop, about an inch of firm travel, then ultra hard. I bench bled the mc before installation and thoroughly gravity bled the system. I've checked all caliper seals, lines, and the master for leaks and all's well there. Only thing I haven't extensively checked for leaks is the hardline the the rears, but I'm not losing any appreciable fluid.

    I went with the S12 mc because I read that the split point was favorable to a set up like mine with bigger calipers up front. I wonder though if the split point of the S12 bmc is different from the Z31 bmc, which seems to be the recommended one for my setup.

    Any thoughts would be appreciated.

  • #2
    What diameter piston is the J30 caliper vs. stock, and what is the bore of the S12 BMC?

    It sounds like you have too small of a MC bore for your piston size to me.
    '18 Chevrolet Volt - Electric fun hatch for DD duty!

    DefSport Koni Sleeve and Spring Perch Buy!!!


    • #3
      you could still have an air bubble in the lines, but it really doesn't sound like there's much of a problem to me.
      Originally posted by SoSideways
      I don't care what color they are as long as they are LONG AND HARD.
      '04 G35 Sedan 6MT- The DD
      '96 240SX- The Track Toy


      • #4
        each j30 caliper is 2x 42.8mm pistons

        s12 uses the BM44 master - 15/16"

        it may not be a problem at all once I switch to decent pads and get used to it, just wanted to get some opinions


        • #5
          Some pads have a lot of compressibility, they can almost feel like air in the lines at their worst.

          Still sounds like a pressure mismatch to me.

          Air in the lines will never really firm up much.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!

          DefSport Koni Sleeve and Spring Perch Buy!!!