My daughter's mountain bike has disk brakes that are rubbing. They're not really binding but you can hear them rubbing. Is that normal? If not, how do I fix it? IIRC, they are hydraulic brakes. I remember having to toe-in the pads, too, to stop the squealing.

Any thoughts on what to do would be appreciated. The bike is a TREK that is maybe as much as 10 years old but is essentially unused.

Constant or intermittent rub?

Spin the wheel slowly and look closely at the rotor passing through the caliper to see if it's spinning true.

Are the pistons retracting when the brake lever is released?

I've never heard of toeing-in disc brake pads. Only on calipers and V's.
You can try loosening the quick-release, then hold down the brake lever then while holding down the lever re-tighten the quick release.
Another trick is to loosen the two bolts holding down the brake housing, press the lever, then tighten the bolts.
You can also push the pistons back but make sure you use something blunt so as not to damage anything.

1) Make sure the wheel is centered and tight in the fork/dropouts. Make sure the pads are not completely worn out.
2) Recenter/reset the brake calipers as mentioned above by loosening the two caliper bolts, squeezing the brake lever and holding it in, and re-tighten the caliper bolts, then releasing the brake lever. Apply and release the brake a few times after again
3) Spin the wheel and see if it is rubbing, if total rubbing go to 4, if just in some spots the rotor might be slightly warped. Find where by slowly spinning the wheel and see where it is hanging and bend the disc a little by hand the other way or with some device that will not damage it (do not use a metal pair of pliers for example. pliers wrapped with some cloth can work in a pinch. It can take a lot of force but don't go crazy Wipe any hand grease, oil off the rotor when you are done.

4) If it is constantly rubbing and not just in some spots, recheck 1 and 2 above and you will need to research the specific model of caliper for the next steps, maybe it's sticking, bound etc..

The whole process should be a few minutes except for some time to straighten a warped rotor.

The only advice I have to offer on top of what others have suggested (such as the steps given by [MENTION=457449]u235[/MENTION]) is to tighten the bolts a little at a time. Tighten the top one a bit, then the bottom one, then back to top, etc.

Good luck!

I've been away, sorry.

The rub is constant/continuous. It does not seem to be a bent rotor.

I will read and try what's posted above.

The toe-in eliminated a monstrously bad squeal. It was easy and worked. If this is not normal to do, maybe it just gave a fresh surface for braking. The idea came from the TREK customer service dudes. It gopt rid of the squeal.

Tell, me, if you spin the wheel and the brake is not applied, should the rotor pass thru the caliper without any sound at all- not rubbing/touching in any way?

That's the way mine are. No touching, no rubbing, no noise. I usually stick a business card between the rotor and the pads to make some space when re-centering the calipers as described in a previous post.

ty

I have also never heard of setting toe-in on disc brake pads. How do you do it? On rim brake pads it is normal, and the way the pads are mounted is adjustable to accommodate toe-in adjustment. I am not aware of a way to toe-in disc brake pads.