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Old 06-24-10, 03:57 AM   #1
JustinHorne
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Grinding sound when freewheeling (<100 mile Trek 7.3, video included.)

Hey guys. She's due for her 100 mile tuneup this weekend, but I've recently noticed this. Honestly, I Can't remember if it was always there, and I just noticed it, or if it developed. Regardless, when freewheeling, this nasty grinding sound persists. It's not the fenders, they have 100% clearance. I think it has something to do with the hub, as you can hear it when I'm backpeddling at the start of the video. The audio quality isn't amazing, it's really a smooth grinding sound in real life...

Thoughts?
I assume it's not normal, of course. Really just didn't want to sound like an idiot when going into the LBS for the tuneup, and wanted to know what this really is first.

http://www.youtube.com/watch?v=_R817dLgBmI

In the audio, it almost sounds like rubber // the tire is rubbing, but that's not the case. Besides, obviously then it would persist when pedaling, as well as wouldn't exist when just reverse pedaling.

Thoughts?
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Old 06-24-10, 06:05 AM   #2
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Sounds like a little adjustment should take care of the problem. I also noticed a little ghost peddling. Not a big deal. When you take the bike back for the 100 mile checkup let the shop know what you have experienced. They should be able to fix in short order.
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Old 06-24-10, 07:47 AM   #3
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Could be improper alignment of the rear shifter.
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Old 06-24-10, 08:16 AM   #4
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That pulsating rushing sounds looks to be in perfect timing with the rear wheel reflector. You say the noise is a constant rushing sound? Its not a rear derailleur problem if you are not pedaling. If you are just coasting, its got to be the rear wheel or freehub.
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Old 06-24-10, 03:27 PM   #5
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Check to see if the plastic disc behind the cassette is straight. It may be slightly bent, and brushing against the lowest sprocket every revolution.

This occurs when backpedalling because the wheel is not moving, but the cassette is, hence brushing every revolution.
It doesn't occur when pedalling, because both are moving at the same pace.
It would then re-occur when you begin to freewheel/coast, because the cassette is stationary, and the wheel and disc are spinning.

I had a similar thing happen on my step-dad's bike a while ago.
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Old 06-25-10, 02:40 AM   #6
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Quote:
Originally Posted by Luke52 View Post
Check to see if the plastic disc behind the cassette is straight. It may be slightly bent, and brushing against the lowest sprocket every revolution.

This occurs when backpedalling because the wheel is not moving, but the cassette is, hence brushing every revolution.
It doesn't occur when pedalling, because both are moving at the same pace.
It would then re-occur when you begin to freewheel/coast, because the cassette is stationary, and the wheel and disc are spinning.

I had a similar thing happen on my step-dad's bike a while ago.
It's straight, and doesn't appear to be rubbing anything.

Quote:
Originally Posted by tj90 View Post
That pulsating rushing sounds looks to be in perfect timing with the rear wheel reflector. You say the noise is a constant rushing sound? Its not a rear derailleur problem if you are not pedaling. If you are just coasting, its got to be the rear wheel or freehub.
Yeah, seems like it's coming from the actual hub itself. Hard to tell though, don't have someone to hold the bike while I move my head around...

I will take it in either tomorrow or Saturday, see what they say I guess.
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Old 06-25-10, 03:00 PM   #7
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Damn.

Always try to cover the simple solutions first, though
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Old 06-28-10, 07:46 AM   #8
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Can't access YouTube at work so I didn't get to view your video, but what you describe sounds exactly like an issue that I had with my 2009 7.3FX when it had similar milage on it. Turned out the rear axle was bent. My LBS replaced the axle under warranty, and since the repair I've put about 1500 miles on that bike with no further issues.
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