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Cannot get rid of brake drag

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  • Cannot get rid of brake drag

    I've had the same problem across multiple bikes, so I'm aware what (who) the common denominator is in this equation. I'm just out of ideas for things to check. Root cause of the problem on a gs500 was a flake of paint inside the master cylinder had fallen over the return hole. Root cause of the problem on a bandit 1200 was shitty tokico 6 pots corroding and needing a rebuild.

    Problem: A short ride around the block creates brake dragging sounds and a hot disc even without touching the brake lever. With the front wheel in the air, a hearty spin of the front wheel only gets about 1-1.5 turns before coming to a stop. If brake pads are retracted or caliper removed, the same effort returns 5+ turns before the wheel stops.

    Things I've tried to remedy this so far:
    -try new brake pads
    -meticulously clean the caliper and pistons
    -flush and bleed brake fluid with quality stuff of correct grade
    -grease sliding caliper pins and brake pad mounting tabs with bendix brake grease
    -ensure master cylinder is not overfilled
    -ensure master cylinder vent hole is not blocked
    -plane off 1mm from new pads in case they're oversized
    ???

    Send thoughts and prayers
    Originally posted by devolved
    I just crashed into a schoolbus full of kiddies, killed them all, raped them, set them on fire and now I'm pissing on their charred remains.

  • #2
    Warped disc ?


    Sent from my iPhone using Tapatalk

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    • #3
      Push pads back , gently...so they don't contact rotor.

      Spin wheel.

      apply and release brakes--watch pad movement.

      Spin wheel.

      annd then....?
      " Imagination is the seed of life..."

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      • #4
        Some drag is normal. But 1-1.5 turns and a hot disc seems unusual - for the front wheel.

        Are you talking about the front wheel? Is there any sign of pad glazing and, if so, is it on both pads or just one? Have you (carefully, with precautions) tried operating the caliper/s when removed from the disc and checked for smooth movement of all pistons?

        Could be master cylinder seals and it needs a rebuild. Won't be pads. Could be the calipers are sticking because they need a clean out and rebuild.
        Click Link for My Bikes:

        Aprilia RS250
        1985 GSXR750 "Slabbie"

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        • #5
          could be the lack of freeplay at the lever??

          to be fair the M/c piston should be fully retracted with hand off the lever...as should the caliper pistons...although they will be held by the square section seals ( on the rotor to a certain degree )

          Are they floating rotors? are the buttons clean free to move?

          Loosen calipers check again if drag is evident to test for fork/caliper preloads..( bent or twisted fork in triples....can cause misaligned caliper.)

          ( so don't undo...just crack the bolts redo finger tight -- works better if you have an assistant to hold brake lever on) make sure to clean locktite and retorque when done...eh?

          OR might just be simple shit as loud said..
          " Imagination is the seed of life..."

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          • #6
            Thanks for the input guys. I'll check that the forks/disc/caliper/axle are all sitting square and not warped.

            The bike in question is an nc700 with 20k on the clock. We are dealing with the front wheel, which is a nissin 3 pot sliding caliper on what seems to be a fixed disc. The pads I removed are the original nissin pads which had more or less even wear. The bike did sit for a while before I bought it but on the whole it's not super old, abused, or high mileage so that might help with any suggestions.
            Originally posted by devolved
            I just crashed into a schoolbus full of kiddies, killed them all, raped them, set them on fire and now I'm pissing on their charred remains.

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            • #7
              Is it a linked brake system with one piston operated by the rear brake?

              Fixed disc won't "wobble" around and knock the pads back like a floating disc...

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              • #8
                Is it pre 2014?

                Linked brakes-- google says they were dropped after 2014--shit idea on an adventure bike ???? Dunno.
                " Imagination is the seed of life..."

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                • #9
                  I've had those symptoms on my rear brakes before. The cause was old brake hoses. Brake/hydrolic hoses come double skinned to prevent bursting or punctures and sometimes on old brake hoses the inner skin can collapse where you can still force fluid through lever pressure but the return press is doesn't have the force to push pass the collapsed section of hose so the piston retracts so slowly or not at all but will retract easily if you were to lever the pads off the rotor. The symptoms only became significantly noticable when filtering through 15km of rush hour traffic type conditions where I'd be using a lot of rear brake to smooth out my speed in low gears for long distances. Hope that helps

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                  • #10
                    get ya foot off the lever

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                    • #11
                      The mechanism that makes the piston return is the flex of the piston seals at the calliper. Have you replaced them? They get old and stiff over time and flex less.

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                      • #12
                        Originally posted by SomeBloke View Post
                        The mechanism that makes the piston return is the flex of the piston seals at the calliper. Have you replaced them? They get old and stiff over time and flex less.
                        That and the absence of fluid pressure...the master cylinder vent port may be slightly clogged or the piston return sping may be weak
                        Smoke me a kipper...I'll be home in time for breakfast

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                        • #13
                          Originally posted by SomeBloke View Post
                          The mechanism that makes the piston return is the flex of the piston seals at the calliper. Have you replaced them? They get old and stiff over time and flex less.
                          There are two seals - a dust seal and a wiper seal. Neither do what you seem to be describing. If they did then you wouldn't have to push the pistons in to the fully retracted position before changing brake pads - they would already be retracted because of the seals... which they aren't. If this were the case though there would be a large gap between worn pads and rotors, which there is not - even when they're down to metal they'll still be skimming the disc.

                          The dust seal simply keeps brake dust and road dirt from accumulating around the exposed piston, and reaching the wiper seal. It has no strength, it's made of thin rubber, that's why it can tear.

                          Hope that was informative in a nice enough way
                          Click Link for My Bikes:

                          Aprilia RS250
                          1985 GSXR750 "Slabbie"

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                          • #14
                            The seals flex... That's why nominal clearance is tiny. That clearance is seal deflection.

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                            • #15
                              That's an interesting diagram. I'm intrigued, I genuinely had no idea the wiper seal did that. From your post I thought you were suggesting the dust seal sprung the piston back in the whole way. My bad.
                              Click Link for My Bikes:

                              Aprilia RS250
                              1985 GSXR750 "Slabbie"

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