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Derailleur failure

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Derailleur failure

Old 05-04-17, 07:38 PM
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justtrying
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Derailleur failure

I have a Giant CypressDX that I got new last June. Great Entry level bike for a 60+ year old. I have had no problems until riding home from work today. I heard a slight clicking noise from the back wheel. Less then a 1/4 mile later I started to pull I over to check the problem and the back wheel stopped rolling. The derailleur was laying loose on the rear hub. Upon further inspection it look like it just separated from the frame. I never dropped the bike and ride conservately. Any idea what could have caused this. While at work it's kept in a small office with limited access
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Old 05-04-17, 07:59 PM
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RonH
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Sorry to hear this.
Lots of causes but if the hanger is a replaceable type then any Giant dealer can replace and adjust everything for you.
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Old 05-04-17, 08:16 PM
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Do you think you were shifted to the largest cog in the back?

The derailleur arm (the "cage"), with the two pulleys, got too close to the spokes. That was likely the ticking noise. Finally, the cage catches on a spoke, and the wheel rips the derailleur off the bike frame.

That's why many bikes have replaceable "derailleur hangers", a softer aluminum piece that bolts onto the frame and has a threaded hole for the derailleur. It's designed to break before the frame does, but the broken derailleur can still mangle the frame.

The spacing is quite close, there's not much gap between the cage and the spokes. On my bike, I measure slightly less than a 4mm gap! (using a 4mm hex wrench to check the gap.)

There's two main reasons for this cage hooking a spoke:
1. The "low limit" screw on the rear derailleur should have been adjusted to keep the derailleur from going too far inward when it's on the largest ("low gear") cog. This is a critical part of adjusting the gears by the mechanic when the bike was new.

Or
2. The derailleur hanger got bent inward a little, from laying the bike down on the drive side or hitting the rear derailleur body against something.

Way less likely:
3. I'd guess that a stick could get bounced up from the road and catch in the spokes and chain. But this would be very unusual. (And it wouldn't click first.)

Last edited by rm -rf; 05-04-17 at 08:33 PM.
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Old 05-05-17, 04:57 PM
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Thanks to both of you for a timely reply. My wife and son dropped the bike off today at the LBS. No wheels for about a week😤& some money out of my pocket.
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