Brake failure - split pin missing - why?- Mtbr.com
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  1. #1
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    Brake failure - split pin missing - why?

    Hi all,

    I am using Shimano SLX brakes, probably 2011, but definitely recent. They have only about 15-20 hours' use.

    I was having a nice 20-minute, fairly bumpy descent today and was just about at the bottom when I pulled on the brakes and the rear brake lever went right down to the grip with zero braking power. Disconcerting. But fortunately I was able to stop with just the front brake.

    Being a newbie and somewhat confused, I thought I might try pumping the lever to fix it. After a moment, the lever was stuck at full distance away from the grip. And when I rode, the pads (or something - pistons? - is that possible? see below) were constantly rubbing on the rotor. I rode the bike slowly to some public transport and got home that way.

    Now, I've taken the rear wheel off, turned the bike upside down, scratched my head a bit, read some books, drunk a beer, compared the front and rear brakes and then started wondering why it looked like the rear brake pads weren't in the right place.

    Finally, I noticed that the split (or fixing) pin for the rear brake is totally missing. When I look at the one on the front brake, it's slotted through the brake pad holes and then bent over the side, so that it is very hard to imagine it working loose. And, as mentioned, the brake pads then seem to be sticking well out of their expected location.

    My question then... what might have happened here? Is it ever the case that a properly fitted split pin can work loose, and then the brake pads get jarred out of place, resulting in total brake failure?

    Or could the LBS possibly have just forgot to put it in?

    (I'd like to know before I storm into the LBS looking miffed.)

    Second question - let's say I find a replacement pin and look to put everything back in place, is there anything else I might have damaged in this incident that I need to look at or replace?

    Thanks!

  2. #2
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    [QUOTE=tantrumizer]Hi all,

    My question then... what might have happened here? Is it ever the case that a properly fitted split pin can work loose, and then the brake pads get jarred out of place, resulting in total brake failure?

    Is the bike new? Have you ever had the brakes serviced?
    A couple of things could result in the pin faliing out
    - If you reuse a slit pin it can break if is straightened and bent again when reused
    - The pin may never have been bent over in the first place - human error
    - It may never have been installed in the first place. The pads may have stayed in for some time and then fallen out at a random time when in use

    Or could the LBS possibly have just forgot to put it in?
    Yes, Possible but very difficult to prove(I'd like to know before I storm into the LBS looking miffed.)

    Second question - let's say I find a replacement pin and look to put everything back in place, is there anything else I might have damaged in this incident that I need to look at or replace?
    If you rode the bike with piston to rotor contact the rotor could be scored and damaged.
    This would be very evident.
    The pistons in the caliper could also be damaged in the same way.

    I would think that it should be OK, just have a really good look before you simply throw in a new set of pads and a pin.


    On a side note.
    Shimano brakes are SOOOOOO simply o replace pads that any person should be able to do the job in five minutes.
    Read up and DIY, no need to get the LBS involved

  3. #3
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    Thanks jeffgre.

    The bike (and brakes) are 2 months old. The front brake pads have been replaced (my fault with some oil), but the rear brakes haven't been touched before, as far as I know.

    Thanks for the tips on what to look for.

  4. #4
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    Follow-up: went to the LBS and the rotor was fine and the pistons pretty much OK too. And yes, they confirmed - no pin!

    The why? will remain unanswerable it seems. They said it's pretty much impossible for it to fall out while riding, pretty much impossible their mechanic forgot it, pretty much impossible Shimano didn't ship it. And I know it's impossible I plucked it out somehow, because I've never even touched that part of the brake as yet.

    So, in the end I don't know why it happened, but I'll be casting an eye over that pin before riding for a while.

  5. #5
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    Garden gnome strikes again!

    Glad you were able to stop safely though

    <---- Going to check brakes now too....

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