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Chain rubbing on deraileur cage

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Chain rubbing on deraileur cage

Old 09-01-11, 09:05 AM
  #1  
yannisg
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Chain rubbing on deraileur cage

I recently upgraded my crank on by mountain bike. Replaced the BB with Hollow tec II, and the old Deore LX with the new SLX M660. I used the two washers on the right side and one on the left as stated by the tec doc for the 68 mm housing. I retained the same Deore LX front derailleur.
However, when riding in the middle ring and the largest sprocket of the freewheel the chain rubs on the left side of the derailleur cage. If I adjust the derailleur so it does not rub, when I down shift to 3rd smallest sprocket (8-sprocket freewheel) the chain rubs on the right surface of the derailleur cage. I cannot make an adjustment to avoid rubbing of the cage in both these cases. Is there anyway to avoid this situation or is this normal?
Any recommendations appreciated.
Thanks,
YannisG
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Old 09-01-11, 10:06 AM
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Homebrew01
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Normally, you just shift the FD a tiny bit ("trim") as needed while riding to stop the rubbing.
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Old 09-01-11, 02:54 PM
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yannisg
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Homebrew01,
Thanks for yr response.
The only way to "trim" the FD on the go is to adjust the shifter cable adjuster nut. So if you adjust it for one situation it will be off for the other, and you will have to re-adjust again, unless I am missing something.
Pls clarify.
Thanks
YannisG
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Old 09-01-11, 05:08 PM
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CACycling
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MTB shifters don't typically have trim capabilities. You might eliminate it by swapping the FD to a modern one. Aside from that, all you can do is have the FD centered on the middle ring and live with a bit of rub on the largest and smallest cogs.
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Old 09-01-11, 05:32 PM
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Are you sure your bb is 68?
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Old 09-01-11, 08:40 PM
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Originally Posted by CACycling View Post
MTB shifters don't typically have trim capabilities. You might eliminate it by swapping the FD to a modern one. Aside from that, all you can do is have the FD centered on the middle ring and live with a bit of rub on the largest and smallest cogs.
Really ? That's dumb. All fronts shifters should have trim. My mtb is an antique with friction front and indexed rear.
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Old 09-02-11, 12:22 AM
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All the grip shifters I've used on my mountain bikes have been "microshift" for the front, which basically means 3 or 4 clicks between chainrings, allowing a single click to be used to trim. However, I have seen full-index front shifters advertised.

yg - since you've got a new crankset with probably slightly different positioning, I'd make sure to follow the parktool.com FD installation instructions from scratch, doing every step.
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Old 09-02-11, 06:01 AM
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Have you moved your derailleur up or down at all? Many derailleurs are shaped inside their cage. There are ramps and bulges. Just the other day I had to raise a derailler on my seatpost so that the chain would "duck under" one of those bulges and not rub. Watch closely where the chain is going while it rubs. Pay attention to exactly what part of the cage the chain is rubbing against. Sometimes that's not so easy to see. Having the bike in a workstand helps a lot.
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Old 09-02-11, 06:22 AM
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YannisG, If the FD is correctly aligned (worth a double check) try inserting a washer between the inner and outer halves of the FD's cage. Remove the screw at the rear of the cage, install the washer to widen the cage and reinstall the screw.

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Old 09-02-11, 09:00 AM
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yannisg
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Thanks all for responding.
My Shimano FD shift does not have any micro-adjustment. It indexes into small, middle and large chain ring.
My BB housing length is 68 mm which quite standard.
I did have to adjust the height of the FD when I installed the new crank.
I'll try the option of widening the cage with a washer or looking to avoid the cage internal bulges to gain a little more adjustment leeway.
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Old 09-02-11, 11:51 AM
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yannisg
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Bradtx,
I installed a small washer and widened the FD cage. On the workstand, not under load, it looks good.
Thanks,
YannisG
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