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I have a 2017 Cannondale Synapse Carbon Disc 105 with less than 10 hours of ride time on it. (I got it in March as unsold stock from last year) I noticed that after I had ridden for a little while, the rear wheel started squeaking obnoxiously as I rode, even while coasting. After a bit of troubleshooting (i.e. removing the caliper), I determined the rear disc brake was definitely the problem; it was presumably misaligned or something. However, when trying to reinstall the caliper after learning this, I noticed the pads seem too close together, to the point where I had trouble fitting them back around the rotor. Now that I've roughly gotten the rear caliper into position, it is constantly rubbing against the rotor however I align it, and the brake lever feels much tighter. Again, this is a new bike with new Shimano 105 parts and I haven't changed anything out. What happened? How do I recalibrate the brake so it works properly? (If it turns out I somehow ruined something, I still have a warranty tune-up at my dealer where I can get it sorted out)

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    Ah, you squeezed the brake lever while the caliper was off the disk, right? – Daniel R Hicks Apr 25 '18 at 1:38
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As mentioned in comments you most likely applied the brake without the disc between the pads. The pistons advance and do not return all the way to their original position - this is how hydraulic brakes automatically adjust for pad wear.

The pistons can be pushed back in. Remove the pads then use a tire lever to push the pistons back in. Then replace the pads. You should be able to find numerous videos showing you how to do this on YouTube.

You should check your disc is not warped, and then reinstall the caliper unit. Again there are plenty of how-to videos explaining how to align the caliper. One way is to loosen the caliper bolts, apply the brake so that the pads grip the rotor them tighten the bolts, then release the brake.

  • I successfully reset the pistons and reinstalled the brakes, but I've been trying for half an hour and cannot get the brakes recentered on the rotor. This is partly because the tolerances are so small and partly because tightening the brake bolts seems to inevitably shift the brakes to the side enough to ruin the precise alignment. I tried tightening the bolts with the brake engaged like the how-to videos said and it didn't work, again because tightening the bolts moves the brake. What am I supposed to do? – David Pitchford Apr 26 '18 at 3:29
  • @DavidPitchford apply brakes while tightening caliper bolts – Argenti Apparatus Apr 26 '18 at 11:03
  • I used my leg strap to lock my rear brake down while tightening, but the bolts (especially the frontmost one) seem "sticky", moving the caliper to one side as I tighten. I'm going to try cleaning the bolts and caliper off to see if it helps the bolts go in more cleanly. (I assume I'll want to regrease them after I do?) – David Pitchford Apr 26 '18 at 13:38
  • Okay, through a combination of the above measures along with eyeballing the brakes/listening for scraping/seeing if they clamp asymmetrically and making minute adjustments, I managed to get the brakes fairly true. There is still a bit of periodic scraping, probably indicating the rotor is not quite true, but I retrued it as best I could to bring this to a barely-detectable minimum. (Will this improve as the pads wear naturally?) – David Pitchford Apr 26 '18 at 23:49
  • @DavidPitchford is your rear wheel attached with a quick release or a through axle? Canondale was not very clear with this on the product page. – gschenk Apr 28 '18 at 22:01
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Maybe the bike has a factory marriage. It is better to take it to the dealer. We all know that an independent intervention to eliminate a marriage leads to the invalidity of warranty service.

  • What do you mean by "a factory marriage"? I'd assume you mean "warranty" but you use that word elsewhere in your answer. And, once again, I don't see how this answers the question. – David Richerby Apr 27 '18 at 17:01
  • Nope. Bikes have components that need adjusting to keep them in proper working order. unlike automobiles, components that will need adjusting can be adjusted by the owner. – Argenti Apparatus Apr 28 '18 at 23:38

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