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Anyone here rebuilt their ST-40 calipers?

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  • Anyone here rebuilt their ST-40 calipers?

    Got some questions about the pressure seals.



    Thanks!
    Technik Engineering ASA Stage 1.
    Supercharged E46 M54B25.
    2011 NASA TTC So Cal Champion!

  • #2
    Instead of starting a new thread...I'm going to continue with this one instead.

    Rebuilding calipers seem to be a dark art of some kind. It's like you have to take the ring to Mordor in order to qualify or something.

    I rebuilt my Stoptech BBK once before. So I know how to do it. But this second time is really puzzling. There are two piston sizes: 40mm and 34mm. The 34mm ones are still leaking. The dust boots are fragile too and they are already tearing.

    I have asked around what tips are there to install the seals and dustboots. I have followed all tips and advice. Still they leak.

    The one question I have is...are the dust boots absolutely necessary? Because they tear so easily and runs for $6 each! This track car is used for track only and driven on the streets to get gas, to/from track venues. That's it.

    Any help, advice, more tips, greatly appreciated!
    Technik Engineering ASA Stage 1.
    Supercharged E46 M54B25.
    2011 NASA TTC So Cal Champion!

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    • #3
      Your question about the dust boots seems to be pretty common for any caliper. Some run them, some dont. Have you contacted ST? What do they have to say?
      Team Rambling Warrior Poet


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      • #4
        Thanks Ed.

        I am still waiting to hear back from Mike @ ST.

        I removed the 34mm pistons today, inspected them and they look 'ok'. No major scuff marks or impaired surfaces. Really hoping that ST can inspect these instead.
        Technik Engineering ASA Stage 1.
        Supercharged E46 M54B25.
        2011 NASA TTC So Cal Champion!

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        • #5
          I rebuilt my st40's once. I don't remember it being particularly tricky. I used a sneaky trick to extend the pistons on the car with the pedal because I don't have compressed air (put in some completely worn pads, pump pedal, remove calipers, lol).

          I assume you inspected the pistons carefully? I've found that polishing them up with metal polish helps with the inspection and with identifying roughnesses.

          If the pistons are OK then probably there's some damage to the bores, which would be a bummer.

          I did use the boots on the ST40's because it was a street car. They tended to melt, burn, etc. My e36 race car has crappy wilwood calipers and they have no boots at all. That hasn't caused any problems and I expect you'd be OK discarding the boots. Especially if you're in California(?) and don't have to wade the car through rain, slush, ice, salt, etc.

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          • #6
            Yes it shouldn't be that tricky. But somehow it seems so.

            No damages to the pistons nor the bore.

            I have been suspecting that the tolerances on the seals are off. But ST previously said they aren't. So I am quite stuck not knowing what else to do.
            Technik Engineering ASA Stage 1.
            Supercharged E46 M54B25.
            2011 NASA TTC So Cal Champion!

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            • #7
              Is the leakage from all four piston pairs? If so then yes, I'd be suspecting the sizing of the seals too.

              It's hard to believe that they're simply the wrong seals: piston sizes vary by at least 1mm, probably more: the wrong parts just wouldn't fit at all. Odd.

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              • #8
                Only the 34mm are leaking.

                Thing is these are sold as 34mm seals but the tolerances are off. +/- 1mm is a huge tolerance. I am referring to +/-0.25 to 0.4mm, which may sound trivial but can cause fluid leaks.

                ST did mention that they switched vendors a couple of years ago but reckons that the new seals should work.

                In any case, I am hoping ST will get back to me on this....really hoping.
                Technik Engineering ASA Stage 1.
                Supercharged E46 M54B25.
                2011 NASA TTC So Cal Champion!

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