erratic disc brake rub

[Onno]

I'm generally now a fan of disc brakes on my road bike. Something that's been happening since I bought the bike a year ago, though (and which does not happen on my mountain bike, which also has hydraulic disc brakes) is that the brakes rub (and thus make that annoying bing, bing, bing, noise) rather randomly. They can be perfectly silent, and then I hit a small bump, or go down a hill, or do nothing at all, and the back or front brake will suddenly start rubbing. It usually goes away on its own in a minute or so. Sometimes if I jam on the brakes, it will stop. At first I assumed I'd just picked up a bit of dirt, but that can't be the cause, because then it would go away as soon as I squeezed the brakes once. Is one of the pistons loose, or not seating properly?

Is this a common problem? Any ideas on how to fix it?

Thanks!

[unterhausen]

I have this problem on my gravel bike, but I have bb7 on that and I'm pretty sure it's because the spring died. I would check to see if your discs are securely fastened.

[Onno]

I agree that it's as though the discs themselves are loose, but they are centerlocks and I've tightened the lockrings fairly tightly with a wrench. I'll try again, and put grease on the threads first, perhaps...

[unterhausen]

When I first tightened my centerlock discs, I used a standard Shimano bb socket. But they bottom out on the centerlock lock rings and after a while, the lock ring would come loose. I got a wrench instead. I got a Birzman, but I'm sure Park sells similar http://www.birzman.com/products_2.ph...cID=28&Key=129

[yinzerniner]

Originally Posted by Onno

I'm generally now a fan of disc brakes on my road bike. Something that's been happening since I bought the bike a year ago, though (and which does not happen on my mountain bike, which also has hydraulic disc brakes) is that the brakes rub (and thus make that annoying bing, bing, bing, noise) rather randomly. They can be perfectly silent, and then I hit a small bump, or go down a hill, or do nothing at all, and the back or front brake will suddenly start rubbing. It usually goes away on its own in a minute or so. Sometimes if I jam on the brakes, it will stop. At first I assumed I'd just picked up a bit of dirt, but that can't be the cause, because then it would go away as soon as I squeezed the brakes once. Is one of the pistons loose, or not seating properly?

Is this a common problem? Any ideas on how to fix it?

Thanks!

This sounds more like a piston retraction issue rather than a disc rotor issue.

-First, have you done a visual inspection of rotor trueness after you first notice the rubbing/pinging noise?
-If you're unable to do a rotor trueness inspection immediately after experiencing the noise were you able to do one later on, with the bike in a stand?
-Have you cleaned out your pistons and seals recently?
-Have you done a fluid bleed recently?

One of the possible reasons you're noticing this issue on your road vs MTB brakes is that the caliper piston travel is different due to the leverage and travel afforded by the brake levers. Since you have greater pull and leverage with MTB levers the piston clearance from and travel to the pads can be larger. On road calipers the pistons have to be initially setup closer since the brifter brake levers by design don't alloy the same amount of leverage and travel. So if you have dirty pistons and/or fluid they won't retract fully which could induce the noise you hear. On an MTB the margin for error in rotor rub is larger since the clearance is initially larger.

And even then it might be a difference in caliper designs or even manufacturers. Shimano usually has more clearance than SRAM or Campy for road hydraulic.

[dddd]

Evaluating pad clearance issues is best done outside, over a sun-lit sidewalk.
This way, you can find a line of sight through the gaps, and thus evaluate what changes to the alignment might help matters.
The disc should not move to one side, should not appear to bend and should not twist at all as the pads start to push against the disc.
Even the wear of the pads is visible doing it this way.

Using the above method, I have kept even my mechanical calipers performing at their best for off-road riding. These require slight adjustment after every 3-hour ride in our hilly American River Canyon trail network, but doing it outside in the sun lets me home in on the needed tweak(s) to either/both pads so as to have a hard feel at the lever and to have no rubbing when the brakes are released.

[dddd]

One more thing, with hydraulic calipers, sometimes following pad replacement the pads may not self-retract as they should following the usual forcing of the pads into retraction.
In such cases, I flood the piston area with a spray bottle of rubbing alcohol, which seems to allow the seals to re-seat more fully and evenly. The brakes are then good to go so to speak, ready for any final evaluation/adjustment.