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Hyd brakes rub unless I slightly pull back on lever...

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Hyd brakes rub unless I slightly pull back on lever...

Old 09-23-15, 12:45 PM
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Hyd brakes rub unless I slightly pull back on lever...

I just swapped to shimano disc brakes and am having an issue with the front brake rubbing pretty loudly. interestingly, if I apply the slightest amount of pressure to the lever the sound disappears all together. Why would the pad stop rubbing against the rotor when the lever is pulled? Any tips on how to fix this?
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Old 09-23-15, 06:01 PM
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Pulling the lever causes the pistons to extend, so rather than hitting in one place and making a "ting" noise, its now just constant drag.
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Old 09-23-15, 06:53 PM
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you will need to pull the pads and push the pistons in, then put the pads back in. now with a business card between both sides of the rotor and pads install the wheel, pull the brake lever a couple of times and remove the cards. no more brake drag.
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Old 09-24-15, 05:39 AM
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Originally Posted by dr1445
you will need to pull the pads and push the pistons in, then put the pads back in. now with a business card between both sides of the rotor and pads install the wheel, pull the brake lever a couple of times and remove the cards. no more brake drag.
As soon as you pull the lever, after removing the cards, the pads will go back to their original position. The only way to fix a rubbing rotor is to loosen the caliper mounts and center it on the rotor. This can be done by pulling the lever to clamp the caliper to the rotor and tightening the bolts. Sometimes the clamping with the lever thing doesn't work so well and you have to do it by eye. If the rotor only hits on one spot, you can sometimes true it by just pushing the offending spot over with your thumb. If the rotor needs a bit more bending than you can do with your thumb, you can tighten an adjustable wrench on the rotor and use that to bend it.
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Old 09-24-15, 11:24 AM
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nope, the pistons do not return. it is not the same as a car or motorcycle with a fluid reservoir and a check valve to maintain the fluid in the line. that is why bicycle brakes are "bleed" from the bottom with a syringe used to push the fluid up and out a vent tube. the pistons will only travel the amount allowed by the fluid between the pump and piston. once the system is closed no further fluid is added.
edit; if you use the biz cards you will find some slack in the brake lever for the above reason.

Last edited by dr1445; 09-24-15 at 11:28 AM. Reason: added
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Old 09-24-15, 02:56 PM
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Originally Posted by dr1445
nope, the pistons do not return. it is not the same as a car or motorcycle with a fluid reservoir and a check valve to maintain the fluid in the line. that is why bicycle brakes are "bleed" from the bottom with a syringe used to push the fluid up and out a vent tube. the pistons will only travel the amount allowed by the fluid between the pump and piston. once the system is closed no further fluid is added.
edit; if you use the biz cards you will find some slack in the brake lever for the above reason.
Shimano disc brakes are not a closed system. They use a reservoir and they self adjust for pad wear. How do you think the pistons move the pads out to contact your business cards after you push them all the way back? Take your wheel out and pull the lever a few times and let me know what happens.
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Old 09-24-15, 03:36 PM
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Rotor is not Flat?
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Old 09-24-15, 06:48 PM
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My guess is that a corner of one of the pads is dragging on the rotor. When you pull the lever and the pistons start to move the pad tilts slightly and the dragging corner pulls back just enough to clear.
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