Old 11-30-18, 04:07 PM
  #7  
fronesis
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Originally Posted by wgscott
That story is probably worthy of a thread of its own if you have the time...
It was a thread in the "wrenching" section of that other message board. But the summary of it goes like this:

Background – I'm a pretty decent amateur mechanic, but I'm still an amateur; I do all my own wrenching and have built half a dozen bikes from the frame up, and dealt with Shimano hydro brakes a few times, but not SRAM.

1. Setting up bike and COULD NOT for the life of me get the caliper to center on the rotor. This is always fiddly, but it seemed impossible.

2. When I finally did appear to get the caliper centered on the rotor, with no rub, all it would take to mess this up is to let the wheel bounce a few inches off the shop floor (or hit any small bump on the road). At that point the rotor would appear to hit the brake pad retaining spring. There was NO WAY to correct. I thought it might be a problem with the rotors, or for the frame and caliper specs, or...

3. The brad pads and retaining spring were brand new, of course, and they looked fine.

4. But not knowing what else to try, I bought a new set of SRAM road pads and put them in. Problem solved.

It turns out the problem was the brake pad spring. The one that came with the new bike was too narrow at the top and too loose as a spring. It didn't press the pads back far enough, making it almost impossible to center the caliper on the rotor. And even when the caliper was centered, it would slide down and hit the rotor directly.

The spring with the new pads looked almost the same, but it was different: it didn't narrow above the pads the way the original did, and it had FAR more spring. Put the new pads in and it was immediately obvious that I had way more room to center the caliper. On the old spring the spring would slide up and down above and below the pads. On the new spring, the pads and spring float together as one unit, and the rotor never hits the spring.

With hindsight, it was easy to see that I had the wrong spring. But in the process, it was not at all obvious that that was the problem. The old spring and the new looked almost identical.
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