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Is disc brake rub normal during break-in period?

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Is disc brake rub normal during break-in period?

Old 06-08-10, 01:41 PM
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xfimpg
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Is disc brake rub normal during break-in period?

My ride is a Giant Anthem X4 with Shimano Deore disc brakes.

I tend to get slight rubbing in the front and the back, even after the "unscrew-brake-clamp-screw-brake" adjustment to line up the pads.

Is it possible that the rubbing will go away after the break-in period?

If so, how many miles does a typical break-in period last?

Last edited by xfimpg; 06-08-10 at 02:09 PM.
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Old 06-08-10, 04:31 PM
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rubbing is not normal
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Old 06-08-10, 05:12 PM
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Originally Posted by reptilezs View Post
rubbing is not normal
That depends on how much it's rubbing.

If it's dragging and preventing the wheel from spinning freely, then no, it's not normal.

If it's a slight scrape or ping once every rotation, which has no effect on speed or resistance, it's perfectly normal. Brake rotors, by nature, are almost never perfectly true, therefore they have a wobble back and forth as they spin. Add this to fresh pads with plenty of meat on them, which would mean very little clearance between the pads, and you get the rotor brushing against the pads.

As I said before, if it's just a slight rub which isn't causing any extra resistance, then it's fine. Just leave it, and it will eventually go away as the pads begin to wear down through regular use.
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Old 06-08-10, 05:18 PM
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Originally Posted by Luke52 View Post
If it's a slight scrape or ping once every rotation, which has no effect on speed or resistance, it's perfectly normal.
This pretty much describes it. There is a slight slowdown with wheelspin, but I don't think i'd notice it affecting my speed.

Thanks
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Old 06-08-10, 05:31 PM
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Are these one sided calipers with one fixed pad or do both sides have pistons?

If one sided it's normal for the fixed pad to lightly skim the rotor. You can carefully flex the worst spots so they just barely kiss the pad but for proper operation the single sided calipers have to have the fixed pad within a thou or so of the rotor. And at that point it's all but impossible to avoid the odd skim sound. If you give it some clearance then the rotor needs to flex too much when putting the brakes on and you don't see the best performance.

If they are two piston calipers then it may be that the screws are kicking the caliper slightly as you tighten them. Watch for movement.

Finally there's a good chance that the calipers are not sitting totally in line with the rotor due to paint on the frame mount points. Scrape off the paint where the adapters mount and see if that helps. If this is an issue careful sighting along the pad to rotor gap can often show an angle is involved. With luck removing the paint from the mounting pad points will fix this and your alignment will be spot on. When spot on the slight retraction of the pads is enough to avoid most scuffing. But at that point you would want to flex the rotor to gently bend it so that the swept surface runs dead on true.
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Old 06-08-10, 05:32 PM
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Originally Posted by Luke52 View Post
That depends on how much it's rubbing.

If it's dragging and preventing the wheel from spinning freely, then no, it's not normal.

If it's a slight scrape or ping once every rotation, which has no effect on speed or resistance, it's perfectly normal. Brake rotors, by nature, are almost never perfectly true, therefore they have a wobble back and forth as they spin. Add this to fresh pads with plenty of meat on them, which would mean very little clearance between the pads, and you get the rotor brushing against the pads.

As I said before, if it's just a slight rub which isn't causing any extra resistance, then it's fine. Just leave it, and it will eventually go away as the pads begin to wear down through regular use.
rotors must be trued, rubbing is not normal
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Old 06-08-10, 06:15 PM
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Originally Posted by BCRider View Post
Are these one sided calipers with one fixed pad or do both sides have pistons?

If one sided it's normal for the fixed pad to lightly skim the rotor. You can carefully flex the worst spots so they just barely kiss the pad but for proper operation the single sided calipers have to have the fixed pad within a thou or so of the rotor. And at that point it's all but impossible to avoid the odd skim sound. If you give it some clearance then the rotor needs to flex too much when putting the brakes on and you don't see the best performance.

If they are two piston calipers then it may be that the screws are kicking the caliper slightly as you tighten them. Watch for movement.

Finally there's a good chance that the calipers are not sitting totally in line with the rotor due to paint on the frame mount points. Scrape off the paint where the adapters mount and see if that helps. If this is an issue careful sighting along the pad to rotor gap can often show an angle is involved. With luck removing the paint from the mounting pad points will fix this and your alignment will be spot on. When spot on the slight retraction of the pads is enough to avoid most scuffing. But at that point you would want to flex the rotor to gently bend it so that the swept surface runs dead on true.
These are the two piston model (Shimano Deore 2010). I checked the rotors and they are straight.
I noticed that the pistons don't retract back in their place as well as they used to.
Even if I push the pads in and separate them using a flat screwdriver, the moment I apply the brakes they clamp the rotor and then don't retract enough and the rubbing starts.
So what I did is open up the metal clip that houses the two pads, thinking that it would create a wider gap between pads. No such luck.

Edit: Just wanted to add that I have about 200 miles on this bike, purchased this spring.

Edit 2: I have two different wheelsets (Mavic 117's and 317's), both have Shimano 160 rotors and I have the same rubbing problem on both. The rubbing is pretty identical on front and back wheels.

Last edited by xfimpg; 06-08-10 at 06:20 PM.
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Old 06-08-10, 06:18 PM
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Originally Posted by reptilezs View Post
rotors must be trued, rubbing is not normal
I did check the rotors and they are straight.
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Old 06-08-10, 07:36 PM
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Originally Posted by reptilezs View Post
rotors must be trued, rubbing is not normal
I don't believe in truing rotors unless they are hugely out of shape.

Seriously, I don't think I've ever seen a brake with perfectly true rotors. Just by their nature, and the nature of the work they do, it's quite normal and acceptable to have a few millimetres of wobble in the rotation.
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Old 06-09-10, 08:22 AM
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Originally Posted by Luke52 View Post
I don't believe in truing rotors unless they are hugely out of shape.

Seriously, I don't think I've ever seen a brake with perfectly true rotors. Just by their nature, and the nature of the work they do, it's quite normal and acceptable to have a few millimetres of wobble in the rotation.
I would agree on principle with you, makes sense. 1.6mm rotors are pretty thin.

Does anyone know if there is a specific adjustment for getting the pistons to retract farther in?
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Old 06-09-10, 01:57 PM
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you should be able to adjust it with the barrel adjuster on the brake lever. at least for mechanical discs, the anthem uses hydros but i still think those adjusters are there.

maybe the lines need to be bled?
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Old 06-09-10, 02:03 PM
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Disk brakes are zero clearance brakes. When you release a hydraulic brake it should just come off the rotor. If there is a huge gap between the pads and the rotors then the rotors are truly warped. There isn't anything to force the pads away with hydraulic disk brakes. No springs, the hydraulic fluid doesn't suck the brake cylinders back, the pressure is just released.
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Old 06-09-10, 03:34 PM
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Originally Posted by DavyC412 View Post
you should be able to adjust it with the barrel adjuster on the brake lever. at least for mechanical discs, the anthem uses hydros but i still think those adjusters are there.

maybe the lines need to be bled?
Hydraulic brakes don't have barrel adjusters....

There are some brakes with reach adjustment on the lever, but this is only reach adjustment and doesn't have an impact on the braking power as such.

Plus there is no reason at all to bleed the brakes here. If there is very slight rubbing, but the brakes still function well and stop with power, and the lever feels firm, there is no need to bleed. On top of that, the fact that this thread is about the break-in period leaves me to think that the bike is pretty new, therefore the brakes would not need bleeding.
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Old 06-09-10, 03:41 PM
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On motorcycles disc brakes are zero clearance. But all the MTB fluid brakes I've seen have retractor springs to open up a small gap. The gap should be somewhere in the range of from the thickness of a buisiness card to about 0.7 mm depending on the system and state of the pads.

Since these have been used for a few months I'm going to guess that some dirt and muck has gotten into the calipers and that they are making the pistons stick on the seals. So it's time to clean them. Soap and water is one option and an aerosol can of brake cleaner solvent is another. I've used the brake cleaner with good results. To do this I drop the wheels and then put a popsicle stick between the pads and pull the lever. This extends the pistons out a little but won't risk popping them out. Spray the areas around the pistons vigoursly. Wear safety glasses 'cause the solvent is going to splatter all over and it stings like heck if you get any in your eyes. Once sprayed down hold the lever for a little longer for the cleaner to drip off and evaporate. Try the brakes again. If they are still not moving evenly then use the popsicle stick or whatever you have to mush the pistons in and out. By now they should be moving equally and retracting nicely.

If you use soap and water then do not use a hard jet of water to try to blast away anything The hose produces enough pressure to shoot water in past the seal if you hit it just right. The brake cleaner solvent doesn't have that much pressure but even then I would not stick the end of the spray tube right by the skirt of the piston either.
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Old 06-09-10, 05:02 PM
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I have a pair of Shimano XTR hydraulic brakes model BR-M965. After 5 years of use, I've learned a few tricks. First, I noticed that one piston retracts more than the other and if I recall correctly, it's the one closer to the brake line port. I've used various combinations of shims to center the rotor in the pad gap. The other thing that seems to help a little is a Q-tip soaked with alcohol. I use it to clean the gunk around the pistons. I might try Magura next time around. Good luck.
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Old 06-09-10, 09:12 PM
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First question is how is the rotor hitting? When the rub occurs, is it on one side with extra room on the other side? Does it only do it at certain points? Does your caliper have tilting ability along with the side to side adjustment?

I have found the "pull brake and tighten down" tactic to be hit or miss fix which I have found mostly miss. What you can do (more easily if the caliper doesn't doing do a vertical tilt) is slightly loosen both screws, use your eye sight down the caliper through a few angles to put the rotor directly centered on one end of the pad. When you have done this, tighten down the corresponding screw just enough to hold it in place but still allowing the other side to more slightly. Then, adjust the other side the same way and tighten that down slightly. you may want to go back and forth a few times to make sure nothing has shifted. Now go back and forth, tightening the bolts little by little, while making sure the caliper doesn't move. if this works right and the rotor isn't bent, the brake should be adjusted as long as there isnt a bigger issue.
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Old 06-09-10, 09:37 PM
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Originally Posted by Luke52 View Post
I don't believe in truing rotors unless they are hugely out of shape.

Seriously, I don't think I've ever seen a brake with perfectly true rotors. Just by their nature, and the nature of the work they do, it's quite normal and acceptable to have a few millimetres of wobble in the rotation.
There's no reason why a disc should ever have a few millemetres of wobble. That's pretty bad for a rim brake, let alone a disc. Personally, I can't stand a brake that makes noise.

Like zjk says, the "pull brake and tighten down" doesn't always work, but I've found it to be worth a try. I use a toe strap to clamp the lever in place while I'm tightening the caliper bolts. If you get that intermittent "zing......zing..." noise of rotor rub when you release the lever and spin the wheel, you're probably close enough, just give the rotor a slight truing and you're good. It's when the disc rubs the whole way round that you know it didn't work.

Find the part of the disc that's hitting the pads, look through the calipers to see which side it's hitting and bend it gently in the opposite direction. The proper tool is basically a chunk of metal with a slot in it, but an adjustable wrench works fine. You'll get the feel for how much you have to bend it to make the adjustment, it's like truing a wheel except much easier.
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Old 06-10-10, 02:01 AM
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Once again, as I said, I don't believe in truing rotors. They're never going to stay perfectly true, and having one or two millimetres of wobble in their rotation will not affect their performance at all, which is why I believe it to be a pointless, unneccessary process.
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Old 06-10-10, 12:48 PM
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Folks, you've pointed me to the problem. If you look at the middle clip, it isnt centered, which means that one of pads is closer to the rotor, and rubbing.
I'll fix this tonite and report back.





EDIT: By the way, does anyone know what the plastic clip around the left screw is used for?
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Old 06-10-10, 03:25 PM
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Originally Posted by xfimpg View Post
Folks, you've pointed me to the problem. If you look at the middle clip, it isnt centered, which means that one of pads is closer to the rotor, and rubbing.
I'll fix this tonite and report back.





EDIT: By the way, does anyone know what the plastic clip around the left screw is used for?
That plastic clip is supposed to prevent the bolt from loosening or undoing itself over time. I don't use them, and I've never had an issue.

From your first post, it's clear you know how to align it. Just loosen those two bolts which hold the caliper on to the mount, wiggle the caliper around a bit, squeeze the brake lever a few times, hold the brake on, and tighten.

To make it easier...

https://www.bv.com.au/forums/viewtopic.php?f=22&t=18848

Happy tinkering.
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