Disc brake rub - try bending the spring
Moderator: robbosmans
The return spring helps to align the brake pad to the piston. It doesn't push back anything. You could also remove the spring entirely and the piston would still retract like before. But the brake pad would then make a lot of rubbing and also clicking noise while riding since it would vibrate and move around a lot.
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And yet one needs to use a fair bit of finger force to squeeze the pads together when installing them. Are you saying that force does not contribute at all to retraction? That force has to go somewhere.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.
The spring is there to aid in retracting the pads, not the pistons. And to keep the pads in place of course. But the pads have no particular reason to approach the rotor except gravity, and that force is fairly low on such a lightweight and mostly vertically aligned thing as the pads.
As others have said, the main cause of rubbing is usually sticky/unevenly retracting pistons, which will in turn over time make one of the pistons rest closer to the rotor. The other causes I've had are misalignment, flexy fork/hub and warped rotors.
That being said, I've had no issues after changing to a bike with a more rigid fork/hub, the extra clearance of the Ultegra 8100-series calipers, Hope self-truing rotors, as well as cleaning the pistons every few hundred km.
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I can’t stress the bolded bit enough. This is so often overlooked and also one of the reasons why pad gaps shouldn’t necessarily be symmetrical. Forks and hubs flex more in one direction than the other. Aero bike forks have more lateral flex than others.
My DT hubs pretty much eliminated any slight chance of rotor rub and my White Industries hub needed the correct amount of preload to completely eliminate rub.
So I guess it is pretty amazing that my fork and hub are stiff enough when the piston is fully retracted, and then suddenly not stiff enough when the piston is a bit sticky. Seriously, indeed the more that every part of the bike resists twisting forces, the better - no argument on that.
All I know is I bent a spring and the rubbing stopped (despite the fact that apparently the spring only presses on the pad and magically applies no force to the piston behind it. )
Well, the groupset will be on a new bike tomorrow so perhaps I can do this all over again.
All I know is I bent a spring and the rubbing stopped (despite the fact that apparently the spring only presses on the pad and magically applies no force to the piston behind it. )
Well, the groupset will be on a new bike tomorrow so perhaps I can do this all over again.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.
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Mr.Gib wrote: ↑Thu Sep 29, 2022 3:53 amSo I guess it is pretty amazing that my fork and hub are stiff enough when the piston is fully retracted, and then suddenly not stiff enough when the piston is a bit sticky. Seriously, indeed the more that every part of the bike resists twisting forces, the better - no argument on that.
All I know is I bent a spring and the rubbing stopped (despite the fact that apparently the spring only presses on the pad and magically applies no force to the piston behind it. )
Well, the groupset will be on a new bike tomorrow so perhaps I can do this all over again.
I mean yes, the pad spring is applying a tiny bit of additional force against the piston, so in an extremely marginal situation it might help a little.
But you shouldn't have to resort to this. A proper diagnosis and appropriate fix is in order.
100% agree and would add that a better design and execution from the manufacturer is also in order.TobinHatesYou wrote: ↑Thu Sep 29, 2022 4:03 amI mean yes, the pad spring is applying a tiny bit of additional force against the piston, so in an extremely marginal situation it might help a little.
But you shouldn't have to resort to this. A proper diagnosis and appropriate fix is in order.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.