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Discussion Starter · #1 · (Edited)
from the back tires when I lift up the rear and spin the tire. I was gonna ride to work today but a block from home I heard this scraping sound. I got off and checked the brake pads--nope, not rubbing. I then rode around and played with the shifter...still heard the sound. I rode back home and checked the skewer and the rear tire is on securely. The sound is like a scraping sound that happens at a certain point in the tire revolution (it's not a constant sound). I was looking for a stray wire that may be brushing against the spokes or rotor, but I didn't find any. I don't know if it's coming from the brake side or the cassette side. I know nothing about wheel hubs, but methinks it may be the hub. This rear tire is a mavic 117 with Shimano disc hub, and it's practically brand new! Grrrrr. Please help!

Bike nerds--activate!

edit to add: bike is a 2000 Specialized FSR Enduro
 

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There is nothing wrong with your bike. It is just a FS bike trying to stop you from riding it on the road, it has a mind of its own!
 

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Discussion Starter · #5 ·
hey, guys. okay, I'm sure the scraping sound is coming from the disc/caliper area. I noticed that when I move the outer pad farther away from the rotor, the metallic sound comes, but when I move the pad closer to the rotor (almost touching it), the metallic scraping sound disappears, though I still can hear some sound (but it's not that metallic sound). Looking from the back, I can see the pads are not touching the rotor; there is a space on either side of the rotor. But I still hear the scraping sound when I lift the rear tire and spin it! How do I get rid of this sound? I don't think my rotors are warped because they are still very brand new, and I haven't done any extreme biking or put a lot of stress on the bike since getting rear disc. Is this normal? Can I just ride my bike with this sound?
 

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djork said:
hey, guys. okay, I'm sure the scraping sound is coming from the disc/caliper area. I noticed that when I move the outer pad farther away from the rotor, the metallic sound comes, but when I move the pad closer to the rotor (almost touching it), the metallic scraping sound disappears, though I still can hear some sound (but it's not that metallic sound). Looking from the back, I can see the pads are not touching the rotor; there is a space on either side of the rotor. But I still hear the scraping sound when I lift the rear tire and spin it! How do I get rid of this sound? I don't think my rotors are warped because they are still very brand new, and I haven't done any extreme biking or put a lot of stress on the bike since getting rear disc. Is this normal? Can I just ride my bike with this sound?
have you removed the rear wheel lately? if so loosen the skewer and make sure the axle is all the way into the frame on both sides. if it still makes noise check to see if the rotor got wacked and bent, usually you can bend it back. If everything above is ok
loosen the bolts holding the brake caliper to the frame, apply brakes, while appling brakes re tighten bolts.
that should do it
 

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Big ring = No chainsuck
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Even if the disc is rubbing lightly, you can still ride the bike. I don't think that the hub would make a suond like that if the bike is fairly new. However, to check it, take the wheel off, and spin the hubs in your fingers. The axle should spin silently and smoothly, with just a little bit of drag.
 

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If all else fails, the rotor itself could be out of round, and rubbing not on the pads, but on the caliper itself.
 

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Discussion Starter · #9 ·
If all else fails, the rotor itself could be out of round, and rubbing not on the pads, but on the caliper itself.

Bingo, that's what it was. I went to my LBS where I got the disc brake the other day. The bike mech. was really helpful and looked at my bike. He tweaked it a bit and then said something about the pads rubbing, but I wasn't too satisfied with that answer because the pads weren't rubbing! I know there was clearance on either side of the rotor! The noise was gone for the time being, and I was just happy. However, before I rode back home, I tested the rear wheel again for any weird metallic scraping sound. It was back. And so I went back, feeling a bit bad about having to bother him again. He put the bike on the stand again and after spinning the rear wheel, he found out the problem was that the rotor is not completely round! I asked if this was a manufacturer defect, and he said no...or something to that effect. What? How common is this? He said the problem can be fixed by raising the caliper up just a mm up from the black brake mount using two washers. He can do this for $12. I decided to do this myself. Two questions:

1. I got the disc from them and had it mounted by them about two and a half months ago. Should they fix the problem free of charge?

2. Is riding with a rotor that is not truly round bad for the brake unit? Does it pose a safety issue? If yes, should they replace the rotor free of charge? Or is this a negligible problem?

I went home and fixed the problem myself gratis. Thanks y'all.
 

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There will be some warping. No bike rotor is truly flat, especially after a few miles of weed-whacking. Bend it back.

But, it sounds like you are describing radial runout as the problem. The outer edge of the disk was rubbing on the throat of the caliper, right? If the $12 was just for labor on a disk that they sold or installed, then I'd take my business elsewhere. That's so ticky-tack for a shim they should have installed in the first place.
 

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If they installed the thing in the first place, they should fix it no charge. Might require you bringing the receipt for the install work to prove your point. Rotors don't just go out of round during the course of normal, or even abusive, riding. Warping, yes...but this is not a result of that. No rotor is perfectly round...there will always be imperfections. The less expensive the rotors, the more variance you will find. I'm not entirely sure how much variance would constitute a manufacturer's defect...it depends on the manufacturer's quality control standards, I suppose.

However, since your particular model uses a post mount style caliper and a couple of shims solves the problem, then I wouldn't be too terribly worried. My disc brakes are Maguras with the international standard-type mount. Shims allow me to adjust my calipers laterally. I have no adjustment vertically. For me, an out of round rotor would result in a phone call to the manufacturer (where they'd probably tell me to take a file to the portion of the rotor that is doing the rubbing).

I'm not sure how much damage it would cause to your caliper if you just let the rotor be. If it's a cable-actuated disc brake, it's pretty unlikely that any damage would result in a problem. However, if you have a dual piston hydraulic brake, I could see the potential for the grinding rotor to compromise the caliper and cause a fluid leak. Since you caught this problem and got it fixed fairly soon, I wouldn't worry.
 

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Old man on a bike
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So the shop only on the third try noticed the rotor rubbing, then wanted to charge you $12 to shim it? Find another shop...
 

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Bikinfoolferlife said:
So the shop only on the third try noticed the rotor rubbing, then wanted to charge you $12 to shim it? Find another shop...
I'll say!

This shop sold you a BRAND NEW 2000 FSR??????????????? WTF is up with THAT?!?!?!?!! A 5 year old bike, brand new? Is it a bike shop, or one of those... ah, nevermind. :rolleyes:

Seriously, find another shop. If they're telling you it's not a manufacturer's defect then they have no clue about how the business works. They're just yammering BS to get your cash. It take's them 3 tries to find the problem? Doesn't sound too thorough if you ask me (and nevermind the "it takes a few tries" crap from the mech's!).

What kind of brake's are these, Djork??? Avid? Hayes? I bet if you talk with the manufacturer you'll get some help. ;)
 
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