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  1. #1
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    Reputation: Micka's Avatar
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    Cheap pads damaged piston ('04 XT & Fibrax Semi-Metallic)

    First up, these are '04 generation XT discs (new in '05), 180mm front rotor.
    I put some new brake pads in the front brake pre-ride yesterday, some cheap Fibrax ones I had picked up online.

    Before I took off into the trails, I did a lap on the criterium track and cycled the front brake on the downhills to bed the new pads in, during this I noticed material actually flaking off the pads something I hadn't seen before and was of concern...

    During the ride, the pads felt dead for quite a while, gradually improving in feel throughout the ride.

    This evening I pulled them out to check the wear (because of the flaking material I had seen when bedding them in) and here is how they look, after about 3 hours of riding. Conditions were dry, rotors were clean.
    IMG_2284-edit.jpg

    For reference, here's what a new pair of Goodridge pads looks like
    IMG_2285-edit.jpg

    When I pulled them out, I saw this on the back of one of the pads. Note the material stuck to the metal.
    IMG_2286-edit.jpg

    Here's what the piston looks like
    IMG_2288-edit.jpg

    The painted metal pad backing has completely transferred itself off the pad onto the piston, and also managed to remove a fragment of the piston (stuck to the pad in the third pic).

    My current theory is the cheap pads used cheap paint on cheap unprepared metal (so the paint didn't stick well), combined with the lack of holes in the metal backing plate (see the pic below), which would provide a gap that may prevent this type of pad/piston fusion.

    IMG_2291-edit.jpg

    Moral of the story is you get what you pay for and I will no longer buy cheap pads for two reasons 1) stupidly fast wear and 2) potential to damage the pistons.

    I'll be sanding off the backing paint and sticking the cheap pads back in, they'll probably struggle to last half a dozen rides going on the observed wear rate.

    Couple of quick questions, will the damage to the piston cause any issues? Can I/should I replace the piston?

  2. #2
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    I don't think piston damage will cause problem. I don't think they are expensive to remplace anyway...

  3. #3
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    You should replace the piston, though I tried to search and couldn't find it anywhere so maybe you can't I suppose your next best bet is try the LBS to see if they can fix it. If not I would swap that caliper in back where It won't be too bad if it fails.

  4. #4
    Meh.
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    The caliper will have to be sent back to Shimano.

  5. #5
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    Wow, thats just crazy!
    Let us know what shimano ends up doing for you. I'd also contact the pad company and make a fuss.

  6. #6
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    Thanks for the input guys, I haven't taken it to a shop yet but will do soon. I had a solid ride on it today and performed without fault. However for peace of mind I'll get the piston replaced or get a new caliper. The most likely time it could fail is when I'm really hard on the brakes, which is the worst possible time for failure - not confidence inspiring!

    Anyway, here's a pic of the sanded pads and the recovered piston fragments. Had to use a hammer and cold chisel to dislodge it off the back of the pad.
    IMG_2292-edit.jpg

  7. #7
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    Can you tell what material the piston fragment is made of?

  8. #8
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    it's made of cheese

  9. #9
    Meh.
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    The piston is probably some sort of ABS plastic.

  10. #10
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    I would replace the caliper, you dont know how thin that piston is to begin with and with the high pressure of the fluid behind it could blow through the weakened spot
    as far as warranty its hard to say. Their point would be it wasnt their pads that did the damage. Xt has a 2 year on calipers

  11. #11
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    I don't think that chip will make the piston weaker. Think of the piston as a cup with its "bottom" on the inside of the caliper. The plastic part that chipped sits inside the cup.

  12. #12
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    I wonder if you could fill that spot with epoxy or JB weld and sand it smooth? As long as the filler could withstand heat it might work.

  13. #13
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    Quote Originally Posted by the-one1
    I don't think that chip will make the piston weaker. Think of the piston as a cup with its "bottom" on the inside of the caliper. The plastic part that chipped sits inside the cup.
    actually the "cup" is upside down the bottom is what chipped, with the demand for light weight componets I doubt there is any extra thickness on that piston.
    why take a chance, if it goes it will spew fluid all over your pads and rotor and make a huge mess. you can get a new caliper for $60 online and they come with new pads

  14. #14
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    Quote Originally Posted by XSL_WiLL
    The piston is probably some sort of ABS plastic.
    Hmm, I thought they used phenolics for that. Kind of interesting how they make it and the fillers used... think of pool ball material.
    "It looks flexy"

  15. #15
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    Here you go, This should make some sense. For simplistic sake, I only drew one side of the caliper.

  16. #16
    Meh.
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    Quote Originally Posted by gticlay
    Hmm, I thought they used phenolics for that. Kind of interesting how they make it and the fillers used... think of pool ball material.
    Forgot about that... yeah, that's probably more correct.

  17. #17
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    Why the hell would they make something like that out of plastic? Thats a failure waiting to happen.

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