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I have a 2022 GT Aggressor with mechanical disc brake rubbing on the rear wheel. I tried realignment of the caliper several times and I got the wheel trued. But my brakes still rub in one spot. Does this mean that the rotor is perhaps bent? I just purchased Parktool rotor truing fork but I still can't get the rub to stop. Could it be something else? Or am I just not correctly straightening it?

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  • Do you own an adjustable spanner/crescent wrench ?
    – Criggie
    Commented Apr 21 at 3:02
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    Just to check, the rubbing is intermittent as the wheel turns is it? That's what the title says but your description sounds more like the caliper is off centre, which would cause a constant rub. Also, has anything been done to the hub recently, and is it running sensibly (a loose hub can cause similar problems)
    – Chris H
    Commented Apr 21 at 6:18
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    Could be bent disk, more likely caliper adjustment. Check if the disk is bent. Place a cable tie around the seat stay, cut short and lined up so it just touches the disk. Spin the wheel and look for the disc moving in an out from the tie. If bent disk, please update question with details that make this clear. If disc is not bent, check out parktool.com/en-int/blog/repair-help/…
    – mattnz
    Commented Apr 21 at 9:41
  • Yes I have a rotor truing fork from parktool that I just bought
    – Alison
    Commented May 23 at 6:41

1 Answer 1

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If the rotor is bent, it will contact one of the pads at a certain point (or area) of the rotation, but not all the time. Observe the gap between rotor and brake pad while rotating the wheel. If the gap stays the same throughout the entire rotation, then your rotor is straight.

With mechanical disk brakes, the adjustable pad (the inner, typically) needs to be as close as possible to the rotor, which requires it to be re-adjusted from time to time. The other pad (usually the outer) is moved by pressing the brake lever.

If you have a constant rubbing, and you cannot fix that by relaxing the adjustable (inner) pad, then you need to re-align your caliper. This is typically done by loosening the two bolts. In most cases, adjusting it is easiest when you loosen the caliper screws, then clamp down hard on the brake and tighten the bolts while the brake is closed firmly.
If that doesn't give the desired results, align the caliper manually, and tighten the bolts, while making sure the caliper stays where you want it.

If your rotor is bent, i suggest you start by checking it's thickness first. The rotors i have seen so far have a thickness of 2.0 mm when new, and a minimum thickness of 1.5 mm. If the rotor is bent and is close to it's wear limit (1.6mm or less) i would recommend replacing the rotor. If it's still good you can bend it back into shape. Use any kind of helpful tools, like an adjustable spanner, and try bending it. Start with very little force. It will take some time to find the right amount. The material is quite flexible, but if you overdo it, you bend it too far, and you don't want to create cracks. Those are your brakes, after all.

A note though: Do not touch the rotor with your fingers. It has very sharp bits (that get re-sharpened all the time by use), it gets very hot after use, and most of all, you don't want even the smallest bit of grease or oil on the brake pads. Should you have touched it anyway, make sure to clean it thoroughly, preferably with rubbing alcohol, and let it dry (briefly) before applying the brakes the next time. Should you contaminate your pads with oil or grease, most of the time only replacing them helps.

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  • Re: cleaning the rotor. You can use "brake parts cleaner" which is, despite the name, actually designed for cleaning brake parts (including rotors). You will, however, have to go to an auto parts store (gasp!) to get some.
    – FreeMan
    Commented Apr 24 at 17:57

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