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How to fix brake discs rubbing?

Old 05-01-21, 02:54 PM
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Birdbikes
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How to fix disc brakes rubbing?

I meant disc brakes in title, not sure how to fix.

My new bike has tektro aries mechanical disc brakes.

I noticed the outer brake pads were rubbing against the rotor on the front and back wheels.

i did the method that said to loosen the caliper and then hold the brakes while tightening it, and I thought that fixed the front wheel, but now it spins mostly free, but the pad still rubs against the rotot on one part of the rotation.


​​​​​​the brake pad still rubs against the rotot on the full rotation on the back wheel.

how do I fix it?
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Old 05-01-21, 03:23 PM
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I believe the Aries is a single side/pad moving design. If so the by loosening the caliper mounting bolts, squeezing the lever to lock the caliper WRT the rotor and then tightening the caliper bolts often results in a caliper where the moving side/pad is released from the rotor just fine. But the other, fixed, side/pad is still touching the rotor.

What I do for both single piston/pad moving (most cable controlled calipers) and both piston/pad moving (most hydraulic versions) is the same. I start with the loosened caliper bolts and squeeze the lever then snug (not tighten) the caliper bolts. Then I look at the pads and rotor and the gaps between both on both sides. Often one side rubs or is closer to the rotor then the other. I note in which direction I want the caliper to move. Then I loosen one caliper bolt slightly and nudge that end of the caliper in the direction I noted just before. That bolt gets resnugged and on to the second caliper bolt. Repeat the slight loosening, nudging of the caliper end and resnugging that bolt. This way your are making subtle changes in caliper position in a controlled way. Repeat at either end of the caliper till both pads are clearing the rotor. The fully tighten the bolts to retain this adjustment.

Sometimes when snugging or tightening down the caliper bolts there will be some caliper movement. If so then compensate for this movement by how much you nudge the caliper before the snugging down. Sometimes the pads don't sit parallel to each other within the caliper. Sometimes the caliper/pads won't sit parallel to the rotor. In these cases some compromise might be called for. Sometimes (many times actually) the rotor is not perfectly flat, it's "out of true" and to better reduce (note I didn't say eliminate) rub some rotor bending to better make it spin as flat as you can is called for.

These guidelines should both get a system pretty close to minimal/no rub and a good base line to discover other issues. Andy
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Old 05-02-21, 08:08 AM
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Thanks Andy for the tale of two nudges, controlled small nudge of each end, one at a time .
That makes sense and will make things easier and faster, even though I don't have to touch calipers very often.
cheers
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Old 05-02-21, 10:06 AM
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I used to do Andy's procedure. Lately I've started noting which side rubs after initial lever squeeze centering, and putting a feeler gauge between rotor and pad on that side after loosening both fasteners. Start with a 0.010", and squeeze lever and snug both fasteners. Remove guage and test. Use larger or smaller size if first try doesn't work. With either approach, squeeze the lever a few times before you put the tools away, as you may think you're done, but sometimes you're not done.
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Old 05-03-21, 09:38 PM
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I've had high success rates of very accurate cable actuated disc brake alignment (with one moving pad) by loosening the bolts just enough so it can move, and then completely removing the cable and placing a business card between the fixed pad and the rotor, and tightening it until everything is snug and then tightening the bolts. This should result in a setup with the rotor just barely clearing the fixed pad, and the moving pad not having to move very far at all to begin contact. Of course, you'll need to straighten the rotor if its bent at all.
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Old 05-03-21, 10:36 PM
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Originally Posted by Birdbikes View Post
but the pad still rubs against the rotot on one part of the rotation.
Sounds like the rotor needs truing.

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Old 05-03-21, 11:37 PM
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Originally Posted by Birdbikes View Post
I meant disc brakes in title, not sure how to fix.

My new bike has tektro aries mechanical disc brakes.

I noticed the outer brake pads were rubbing against the rotor on the front and back wheels.

i did the method that said to loosen the caliper and then hold the brakes while tightening it, and I thought that fixed the front wheel, but now it spins mostly free, but the pad still rubs against the rotot on one part of the rotation.


​​​​​​the brake pad still rubs against the rotot on the full rotation on the back wheel.

how do I fix it?
True the rotors. Then adjust as suggested above.
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Old 05-04-21, 04:38 AM
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slide a business card in between the pad & rotor after the assembly is loosened a lot. Once the bc floats in between the space easily, tighten the bolts.
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Old 05-05-21, 01:53 PM
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This is the biggest problem with disc brakes; the constant adjusting to reduce rub - drives me crazy. You would think that manufacturers would be able to figure out how to reduce disc rub. I wonder if motorcyclists have this problem?
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Old 05-05-21, 02:06 PM
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Do pads really get pulled away from the disc on bikes with disc brakes?

I haven't changed mine yet so I don't know. But on a car, at least the ones I've worked on, the brake pads aren't physically connected to the pistons that push them into the rotor. They rely on the ever so slight wobble in the rotor to push them away from them when pressure is relaxed on the piston.

However too much wobble of the rotor is a bad thing. You'll feel it in the brakes on a car. On the other hand, if the rotor amazingly has absolutely no wobble, warpage or run out, it's still not an issue because there is no pressure on the pads.

I'd think bikes would be similar. So if you are just talking about the scrubbing you might hear when moving the bike around, that shouldn't be an issue. It's only if you hear that scrubbing constantly while riding that it's an issue IMO.

But for times you are off the bike just moving it around it doesn't take much rub to make a lot of noise.
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Old 05-05-21, 02:22 PM
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Originally Posted by Iride01 View Post
Do pads really get pulled away from the disc on bikes with disc brakes?

I haven't changed mine yet so I don't know. But on a car, at least the ones I've worked on, the brake pads aren't physically connected to the pistons that push them into the rotor. They rely on the ever so slight wobble in the rotor to push them away from them when pressure is relaxed on the piston.

However too much wobble of the rotor is a bad thing. You'll feel it in the brakes on a car. On the other hand, if the rotor amazingly has absolutely no wobble, warpage or run out, it's still not an issue because there is no pressure on the pads.

I'd think bikes would be similar. So if you are just talking about the scrubbing you might hear when moving the bike around, that shouldn't be an issue. It's only if you hear that scrubbing constantly while riding that it's an issue IMO.

But for times you are off the bike just moving it around it doesn't take much rub to make a lot of noise.
Part of the problem is that the pads are so dang close to the rotors, it doesn't take much to rub. Were it not for the fact that disc brakes work better in rain/wet conditions and generally (IMHO) brake better than rim brakes, I would switch back to rim brakes in a heartbeat...
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Old 05-05-21, 02:36 PM
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Originally Posted by cj3209 View Post
Part of the problem is that the pads are so dang close to the rotors, it doesn't take much to rub. Were it not for the fact that disc brakes work better in rain/wet conditions and generally (IMHO) brake better than rim brakes, I would switch back to rim brakes in a heartbeat...
I don't see that as part of the problem. Though we haven't heard from the OP as to whether or not this is just rubbing noise they hear while moving the bike around in the quietness of their house or garage, or if this is in fact noise while actually riding the bike.

As I said, on cars, there is nothing to pull the pad away from the disc. It's just that the piston is not putting any pressure on the pads anymore. So a microscopic distance is okay to prevent friction that is actually causing one to work harder propelling their bike.
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Old 05-05-21, 02:49 PM
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Originally Posted by Iride01 View Post
I don't see that as part of the problem. Though we haven't heard from the OP as to whether or not this is just rubbing noise they hear while moving the bike around in the quietness of their house or garage, or if this is in fact noise while actually riding the bike.

As I said, on cars, there is nothing to pull the pad away from the disc. It's just that the piston is not putting any pressure on the pads anymore. So a microscopic distance is okay to prevent friction that is actually causing one to work harder propelling their bike.
On disc brakes, the mechanism that pushes the pads against the rotor sometimes gets stuck and that creates the rub. Happened to me once already on a relatively new bike. I just don't understand why companies haven't eliminated brake rub. Also, why not develop an electronic closed braking system in the hub/wheel? Why are we stuck in the 19th century? Where's the innovation? Disc brakes have been around for decades?

On eBikes, for example, the motor could also be used to slow down the wheel. I see this as the next gen for eBikes with more power and battery life.

Maybe I should patent this...lol...
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Old 05-05-21, 02:53 PM
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there are many designs with bicycle calipers. lower cost mechanical calipers tend to have one side that levers the pad into the rotor while the other pad sits stationary. Both pads often use a magnetic attraction to keep the pads from free floating & there's a spring steel clip that acts as additional help that binds the pads away from the rotor. For the one sided lever actuated pad design, the opposing pad may require a slight adjustment every so often to keep the rotor deflection at a minimum during braking.
The double pull lever is what makes adjustments a thing of the past, same goes for hydraulic designs.
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