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A couple days ago I noticed my rear brake didn't seem to be working well, so I bled them to make sure there wasn't any air in them. It didn't have any effect, so I took a closer look and noticed that the caliper seemed to be pressing the pads unevenly, and one pad was nearly gone. I had an new set of pads for the rear on hand, so I changed them and figured I was good.
I went for a test drive, but it still didn't feel quite right. After I got off the bike, I noticed that the caliper was very hot, like the brake was dragging. Then I noticed that once again, the pistons seemed to be pushing the pads unevenly -- the inside piston was extended much farther than the outside piston. I didn't have time to look at it, so I didn't ride it any more.
Today I took a closer look, trying to figure out why the rotor was not centered in the caliper. To the right of the rear wheel, mounted on the axle, is a spacer, followed by the bracket to which the calipers mount. As long as they're all pressed together (they are), the positioning of the caliper relative to the rotor is pretty much fixed (aside from rotation about the axle).
At this point, I started wondering if the mounting bracket for the caliper was bent, but I couldn't see how, and it's a pretty stout piece of metal. Then I thought that maybe the rotor was warped/bent. I held a straight edge to the rotor, and sure enough it was. It's not a wavy bend, but rather like rotor was now concave/convex. On the right side of the rotor (facing the outside), there is a gap between a straight edge and the surface of the rotor. On the left side (facing the inside), it teeter-totters on the surface of the rotor nearest the center. Based on what I see, the outside circumference of the rotor is bent outwards by roughly half the thickness of the rotor.
I am concerned as to how this could have happened, and what you think about fixing it. I'm also worried about removing the rotor from the rear wheel. I started to remove it a month ago when I first got the bike, but the bolts were so ridiculously tight I decided not to for fear of breaking the head off.
In the following pictures, you can see that the rotor is not centered -- the seam separating the two halves of the caliper should line up with the center of the rotor as viewed on edge:
I went for a test drive, but it still didn't feel quite right. After I got off the bike, I noticed that the caliper was very hot, like the brake was dragging. Then I noticed that once again, the pistons seemed to be pushing the pads unevenly -- the inside piston was extended much farther than the outside piston. I didn't have time to look at it, so I didn't ride it any more.
Today I took a closer look, trying to figure out why the rotor was not centered in the caliper. To the right of the rear wheel, mounted on the axle, is a spacer, followed by the bracket to which the calipers mount. As long as they're all pressed together (they are), the positioning of the caliper relative to the rotor is pretty much fixed (aside from rotation about the axle).
At this point, I started wondering if the mounting bracket for the caliper was bent, but I couldn't see how, and it's a pretty stout piece of metal. Then I thought that maybe the rotor was warped/bent. I held a straight edge to the rotor, and sure enough it was. It's not a wavy bend, but rather like rotor was now concave/convex. On the right side of the rotor (facing the outside), there is a gap between a straight edge and the surface of the rotor. On the left side (facing the inside), it teeter-totters on the surface of the rotor nearest the center. Based on what I see, the outside circumference of the rotor is bent outwards by roughly half the thickness of the rotor.
I am concerned as to how this could have happened, and what you think about fixing it. I'm also worried about removing the rotor from the rear wheel. I started to remove it a month ago when I first got the bike, but the bolts were so ridiculously tight I decided not to for fear of breaking the head off.
In the following pictures, you can see that the rotor is not centered -- the seam separating the two halves of the caliper should line up with the center of the rotor as viewed on edge:
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