Rubbing disc brakes

Discuss light weight issues concerning road bikes & parts.
TobinHatesYou
Posts: 4167
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

My brakes only drag for a fraction of a second after a hard stop. It really does not affect anything.

One thing to keep in mind is that given that one piston will always extend and retract slower, you don't necessarily want equal clearance on each side of the rotor.

by Weenie


numberSix
Posts: 92
Joined: Sun Sep 23, 2012 1:53 pm

by numberSix

If you ruled out air in the system and non-square mounting surfaces, there’s an easy fix.

Loosen the caliper bolts.
On the side that rubs, insert a .020” feeler gauge between the pad and rotor face. It needs to run the full length of the pad surface.
Squeeze the brake lever and re-torque the caliper bolts. How firmly you squeeze the lever does have an effect - aim for ‘moderate ‘ pressure. Same for the re-torquing procedure, think how tightening the bolts will try to rotate the caliper body out of parallel to the rotor plane. Alternate bolts and tighten a little at a time.

Caveat: .020” is what works for mtb. I’m not a road disc user. You might need to try other (smaller) shim sizes.

Another overlooked point as the mileage or conditions add up: crud between the pad tabs and caliper body. Occasionally pull the retaining pins and give the mating surfaces a scrub.

6

RocketRacing
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Joined: Thu May 10, 2018 2:43 am

by RocketRacing

Lewn777 wrote:
Fri Sep 13, 2019 5:51 am
wheelbuilder wrote:
Fri Sep 13, 2019 5:00 am
It is going to take riders a long time to come to the realization that the current iteration of disc flat-mount road bikes are not going to be silent all the time. Most of the experiences in these types of threads are coming from individual bike owners and their saga of what the symptoms are and how they remedied it. I know there are several pro mechanics on this site and I can guarantee that our experiences probably entail and endless line of complaining riders with unrealistic expectations.
When I do a long descent and then release the brake..........ting,ting,ting
When I do a panic stop then release the brake....................ting,ting,ting,
When I remove and re-install my front wheel......................ting, ting, ting,
When I climb out of the saddle............... ting, ting, ting
When I sprint......................... ting, ting, ting
When I am JRA...............................................................ting, ting, ting
After I replace pads.........................................................ting, ting, ting
After I bleed the system...................................................ting, ting, ting.

These brakes are going to make noise at some point or another. That I can guarantee you.

Pistons seals expand with heat after a descent or hard stop and the pads rub for a while before the seals contract again. A microscopic bit of road dust gets between the piston and the bore and the piston will not retract fully and the pads will rub. Caliper mounting surface not perfectly surfaced and on an even plane, pads will rub, Didn't torque your T/A to the exact spot as before, pads will rub. It goes on and on. Riders need to lower their expectations in regards to silent road disc operation.

You should go jack up one of the corners of your car and spin the wheel freely......report back on findings.
Lift the front wheel of your motorcycle off the ground and spin the wheel freely.....report back on findings. These systems use comparatively massive fluid systems with huge tolerances and still will sometimes barely turn on their own. A road bikes system is miniscule with basically a couple of drops of fluid in the entire system with very tight tolerances. I'm surprised they even work at all let alone as good as they do.
Oh my god!
So you're saying that all disk brake systems are noisy and drag? So in an environment where every watt counts and weight is important, disk brakes might not be best suited to the application of road bicycles? :shock:
Well, i am getting koms left and right with this new bike, so it is not slowing me down. But i can not help but think it could be faster. I am all about marginal gains.

Nefarious86
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by Nefarious86

I must be doing it wrong, multiple wheel sets and 0 strange noises.

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RocketRacing
Posts: 870
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

Nefarious86 wrote:
Fri Sep 13, 2019 1:47 pm
I must be doing it wrong, multiple wheel sets and 0 strange noises.

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But are they sram brakes?!?

Hahaha

Hexsense
Posts: 933
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

My initial set-up have even more riddiculous rub than your.
My first set-up, only rub when i turn left. Even without load!
For example, spin front wheel off ground then rotate bar to the left. Then it's rubbing. Those top heavy finned brake pads flap over with gravity and push the braking pad into rotor!

But after clean brake piston, re-center brake caliper, reinstall brake pad and spring (more carefully, to make sure spring is nice and centered). Then i got no brake rub ever since.

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

RocketRacing wrote:
Fri Sep 13, 2019 4:28 am
but with wear, the clearance between the rotor and pads will increase in time. So intolerance to warping will be highest in a new system.
Nope. The pistons advance to account for wear in hydraulic systems. So once the initial bedding in plus maybe 50-100km is complete, the clearance should remain constant.

RedbullFiXX
Posts: 110
Joined: Sat Aug 05, 2017 6:13 am

by RedbullFiXX

RocketRacing wrote:
Fri Sep 13, 2019 4:59 pm
Nefarious86 wrote:
Fri Sep 13, 2019 1:47 pm
I must be doing it wrong, multiple wheel sets and 0 strange noises.

Sent from my SM-G977B using Tapatalk
But are they sram brakes?!?

Hahaha
SRAM is all I have
3 bikes, all good

Some friends with Shimano, not so quiet
I do keep things clean though

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corky
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Location: The Surrey Hills

by corky

I believe The fundamental problem with bicycle disc design is that they rely on the deformation of square edged seals to project/retract the pistons when the brake lever is operated. squeeze the lever and the piston is pushed out by the hydraulic fluid, the piston deformes the seal, release the lever and the seal goes back to its original shape and pulls the piston back in.....this means the gap between pad and rotor has to be vey small, because the seals cannot deform/reform very far.( NB the ‘springs’ in the callipers are for pad retention only). .....

I think there needs to be a redesign that utilises another method of piston extension contraction that allows a larger gap between pad and rotor at rest.....I’m sure this has been considered by engineers but discarded because of complexity or weight penalty

For me the noise and rubbing on a road bike is unacceptable and the maintenance required to keep this to a minimum is not worth it. I read somewhere about a disc brake user suffering pad contamination from washing their bike......... boiling brake pads, burning brake pads ...what’s that all about?

ChiZ01
Posts: 311
Joined: Wed Jan 01, 2014 6:20 pm

by ChiZ01

numberSix wrote:
Fri Sep 13, 2019 12:33 pm
If you ruled out air in the system and non-square mounting surfaces, there’s an easy fix.

Loosen the caliper bolts.
On the side that rubs, insert a .020” feeler gauge between the pad and rotor face. It needs to run the full length of the pad surface.
Squeeze the brake lever and re-torque the caliper bolts. How firmly you squeeze the lever does have an effect - aim for ‘moderate ‘ pressure. Same for the re-torquing procedure, think how tightening the bolts will try to rotate the caliper body out of parallel to the rotor plane. Alternate bolts and tighten a little at a time.

Caveat: .020” is what works for mtb. I’m not a road disc user. You might need to try other (smaller) shim sizes.

Another overlooked point as the mileage or conditions add up: crud between the pad tabs and caliper body. Occasionally pull the retaining pins and give the mating surfaces a scrub.

6
that would have worked except OP's caliper moves when the brake is applied which indicates uneven mounting surface

menkar
Posts: 16
Joined: Tue Aug 10, 2010 5:23 am

by menkar

I never loosen the caliper. Once aligned it never needs to be touched.

The pistons act independently of each other thus you can move them independently until they're centered on the rotor. Here is a thread in which I discuss this in detail:

viewtopic.php?p=1502422

bm0p700f
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by bm0p700f

Has the op face the mounts. This is something often overlooked.

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Calnago
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by Calnago

bm0p700f wrote:Has the op face the mounts. This is something often overlooked.
It’s kinda like the first thing that should be done when installing discs, just like aligning a derailleur hanger before slapping the drivetrain on, or facing BB shells etc. Yet, it seems to be one of those things that often gets ignored, even by shops. Then, only if there’s a problem does it get looked at. Makes me wonder how many discs are out there where the mounts weren’t faced, yet the brakes are working ok, kinda sorta, but could be so much better if the mounts they’re sitting on were properly faced.
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backdoor
Posts: 39
Joined: Tue May 21, 2019 9:54 pm

by backdoor

Have you swapped rotors front/back?

Sometimes centerlock rotors don't perfectly true depending on the quality of the rotor and how its attached to the centerlock mechanism.

Same can happen with 6 bolt when the bolts are not properly torqued upon install.


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by Weenie


adilosnave
Posts: 25
Joined: Sat Dec 23, 2017 2:10 pm

by adilosnave

Just going to throw this out there as an idea because I've found it to be the cure for 50% of the slight rotor rub on my wife's mountain bike. Now granted, her fork doesn't feature thru-axle but I've even seen this particular phenomenon on my thru-axle equipped steed.

The fork legs might not be perfectly aligned. I just flip the bike upside-down and sit the front wheel in place while carefully applying slight pressure to the right leg (QR in left.) Wait until I don't hear anything while spinning the wheel and close the lever. Generally works.

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