/ hydraulic disc brakes
Do you mean the Disc ( Rotor ) is rubbing on the pads ? If so you could try removing the back wheel and pushing the pads & calipers apart ( with a flat knife ) then realign the wheel being careful when putting it back in . Give it a spin ( with bike upside down ) to see if still rubbing before tightening . Usually works .
Depends on the type of brake, but typically:
1. the rotor/disc is not true. If the disc is only rubbing intermittently that's the problem. Find where the rub is and you can bend it back into shape using a special tool, or an adjustable spanner. You can do it by hand but DON'T touch the disc, use gloves or a cloth, as oil from your fingers can get on the disc and reduce braking power.
2. the calipers aren't centered properly. There are two allen bolts either end of the caliper holding the unit to the frame. Loosen these a bit until the caliper is free to 'wiggle'. Pull on the brake levers so that the caliper is locked firm against the disc, and tighten the bolts back up.
Usually one or both of these actions will sort the problem out, but the most important thing is to get the discs true. No amount of adjustment will get it 'rub free' with a wobbly disc.
Often they improve once bedded in. You need to generate a couple of heat cycles first. Also some very slight rubbing is pretty normal.
It can be a very quick job to sort, and it's worth learning how, as you may have to do it from time to time. Bike upside down, get the right size of allen key to very slightly loosen the bolts holding the disk brake caliper onto the frame or the u-shaped adapter attached to the frame. There should be a bit of side-to-side play in this.
With you eye directly above it, gently spin the wheel - you may be able to see that the gap is less on one side of the rotor than the other, and a tiny repositioning of the caliper to centre it may eliminate the rotor rub.
If it can't be sorted that way, or it's a warped rotor, the shop needs to sort it for you.
Just don't do what I did last night when holding he caliper with the wheel rotating and stick your finger through one of the holes in the rotor. That's quite painful. Rotor metal is very sharp...
To clarify, adjust the bolts holding the caliper onto the adapter rather than the adapter onto the frame.
I the bike is new and you are not bike-minded, then I'd advise not trying to adjust the set-up, you could well cause more problems.
I'd let them bed in a bit (new pads & disk can rub a bit) and if the rub persist, then pop it back to where you bought it and have a chat with them.
Turn bike upside down and give the wheel a good spin, you should see the rotor spining absolutely true. If it is and you really feel like tinkering with it yourself.
1) find out where its touching from, get a torch to help you.
2) find out (before undoing them) which of the bolts will need to be undone to adjust it in that direction.
3) undo the those bolts until the caliper can be moved, but not so much that its floppy.
4) rotate the wheel checking for rubbing (noise)You can also check this by sliding a paper in the gap too.
5) gradually tighten the bolts carefully and still checking for the rubbing as the caliper may move slightly as you do this or adjust inwards. correct this if necessary as you go on tightening.
If the problem is more serious then this (i.e. rebleeding brake or facing the mounting on the frame) then definitely take it back.
Hope this helps... oh and happy riding!
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