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My front brake rotor is rubbing against the pads as the gap is very narrow between the pads and the wheel is not completely true.

Is it possible to remove the brake pads and enlarge the gap a little bit to avoid rubbing? enter image description here

Matt Morgan
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Ender
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1 Answers1

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Hydraulic disc brakes don't need wheel truing to avoid brake rub. They need three things:

  1. The brake must be properly centered. You can do this by undoing the brake bolts, pressing the brake lever and tightening the brake bolts at the same time you still squeeze the brake lever. If this didn't help, then:
  2. The pistons of the brake caliper must work well. You can observe this by squeezing the brake, seeing whether both left and right piston move equal amounts and retract equal amounts. If it looks like one of the pistons moves less, it's a "lazy" piston. You can fix this by removing the wheel, removing the brake pads, and exercising the "lazy" piston several times, holding the other piston in with a padded tool such as rubber-padded cone wrench handle (like Park Tool SCW), while you alternately press the brake lever several times to move the "lazy" piston out, and again push it in several times with the padded tool. You should also lubricate the seal of the "lazy" piston with a cotton swab soaked in brake fluid. If this didn't help, then:
  3. Is your brake rotor true? If it only rubs in certain positions, it may be out of true, meaning you need to true it. You can do so by observing at which point it rubs, and then moving it to opposite direction with a brake rotor truing tool such as Park Tool DT-2.

Of course if your wheel is grossly out of true, you need to fix it too, but it doesn't create brake rub if you have disc brakes, since disc brakes don't use the rim for braking.

Any attempt to enlarge the gap will fail, since hydraulic brake calipers have self-adjusting pistons. Or most likely it will fail, theoretically it's possible if your problem is a "lazy" piston (2), one movement of the piston could fix it. But in many cases, you need to exercise it several times and also lubricate the piston seal with brake fluid soaked cotton swab.

juhist
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  • I was thinking the rotor would wobble in sync with the wheel if it wasn't trued. Now I added a photo of the front wheel. The gap between the pads seems more narrow than it should be to me. – Ender Jun 25 '23 at 08:14
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    Well theoretically it's possible if someone has pressed the brake without the wheel and rotor in the frame, that the pad gap could become too narrow on both sides. If that's the case then and only then spreading the gap helps. Otherwise, I think you may have a lazy piston, maybe on both sides. – juhist Jun 25 '23 at 08:32
  • I don't have any lubricant but chain lube. I'll take it to a bike shop. Thanks for the help. I'll give an update when I found the cause. – Ender Jun 25 '23 at 08:42
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    Speaking from experience, resetting the pistons (‘spreading the gap’) can also help get things into an optimal state a bit faster if the calipers were severely misaligned. It doesn’t do anything that won’t happen anyway though, it just speeds up the process of getting the pads/pistons realigned properly after realigning the calipers. – Austin Hemmelgarn Jun 25 '23 at 13:05
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    @Ender If you're willing to spend a few minutes to learn how, a $15 bleed kit and $15 bottle of oil will last you a long time and save you many trips to the shop to get basic brake bleeds done. Also, then you have the fluid to use as the lubricant in situations like this. – MaplePanda Jun 26 '23 at 06:44
  • After a close examination of the caliper by myself, I saw that the pistons has corrosion and one of them sticks out more than the other and it doesn't move back in. Maybe due to corrosion? – Ender Jun 26 '23 at 08:56