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#1
04-07-2020, 10:57 AM
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Rear derailleur movement when clamping
Working on a friend's Steven's Cyclocross Team bike (with canti brakes) and noticed that when clamping the rear wheel quick release, there is some movement of the rear derailleur. It's more pronounced toward the bottom of the cage so something is angling it inward toward the wheel when clamped.
The hanger is secured with two allen bolts. Both are tightened. I feel nothing loose in the whole area. RD is brand new. Wonder if this is contributing to the inconsistent shifting in the 3 small cogs. The hanger doesn't look bent but I don't have anything like a Park DAG tool to be certain either. Any insight on what else to look for or how to check without a DAG tool? All shops are currently in lock down so no LBS trips possible. 
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#3
04-07-2020, 11:30 AM
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Yeah, a hanger alignment tool would be invaluable. I would check hub width (and axle end alignment), dropout spacing (again alignment tools would be handy), and the interface between the hanger and the dropout plate.
__________________
You always have a plan on the bus... Last edited by Hindmost; 04-07-2020 at 12:00 PM.
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#4
04-07-2020, 12:34 PM
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Seen that a few times already, you clamp the QRs and the darn RD moves.
You can make yourself a RD tool and get that sucker aligned or non aligned 
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#5
04-07-2020, 01:29 PM
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Taking a closer look, I am wondering if it's some compression, deformation of the hanger. The pics may not do justice but the open part of the dropout has a bit more compressed metal than the upper part. This would be in line with the direction of movement the RD shows when clamping the QR.
The hanger was not secured in with screws in these pics.
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#7
04-07-2020, 01:38 PM
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Do you mean you have a frame showing similar compression of the metal at the dropout/ hanger?
Quote:
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#8
04-07-2020, 02:44 PM
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IN the hanger the only piece that pretty much will deform is the hanger itself, and thats the problem you are having right now. You close the quick release and the hanger shifts itself to the side.
Do as DJ says, put the wheel in there, tight the quick release and then align the hanger. Doesnt need to be super perfect tho. There's other bikes that the bolts fixing the hanger to the drop out are the problem, they touch the hub of can even touch the quick release creating the problem but looks like you dont have that issue. Not that the bike is bad, just does that... good is an easy fix, just take it easy.
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#9
04-07-2020, 03:23 PM
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Looks like you're onto a likely cause. The surface of the dropout that mates with the axle end looks unevenly worn resulting in misalignment when clamped. Easy fix is to simply bend the hanger to compensate.
__________________
You always have a plan on the bus...
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#10
04-07-2020, 03:33 PM
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This is very common with frame with replaceable hangers. The interface between the parts is never what it should be and only when the QR is tight is everything pressed together firmly.
The practical advice given by others is the ticket......put the wheel in and tighten down the QR and then align the hanger. This will assure it's functionally aligned. It will come out of alignment when you remove the wheel but that won't matter...as long as it lined up when the wheel's in place you should be good. dave
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#14
04-08-2020, 09:09 AM
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Quote:
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#15
04-08-2020, 09:27 AM
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Pull the hanger off and look for globs of paint or resin in the recess of the frame. This is usually the root cause. Or the dropout itself isn't square with the non-drive side and when you clamp the wheel in, it pulls it into square. One thing to check, is it just the hanger that's moving or is it the whole dropout?
Like others have said, aligning the hanger as it is will yield respectable results.
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