Bicycle Mechanics - Chain is rubbing the guide ONLY in 1st gear. Please help! (Pics!)
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03-27-08, 08:39 PM
First off, I'm a rookie at bike repair, so please forgive my lack of proper part names. I have a 9spd double that only rubs the inner chain guide while in 1st gear ONLY. The pictures below show what cog and ring the chain is on when it rubs the guide. My question:
What can I adjust to correct this rub? I tried taking pics of the front derailer to hopefully allow you guys to point out the nut that needs adjusting. I would GREATLY appreciate your help. Thank you in advance!
03-27-08, 08:43 PM
Cross chain combo. Normal. You can try unscrewing the low limit screw a bit more at the risk of dropping your chain - you'll need to reset the cable at the anchor point if you do this.
03-27-08, 08:47 PM
It's one of the two travel limit screws in this shot of the upper side of your front derraileur. One of them will let your cage move in a hair so the chain doesn't rub anymore. Sorry I can't say which it is specifically. But if you can find a 105 parts manual it'll say. Or you can look down inside the arms to see which screw is touching an arm and just back that one out a little. Or just pick a screw and turn it 1/2 turn. If nothing happens then turn it back to where it started and turn the other a half turn. If it moves then that's the one. Turn it so the cage moves inward just barely far enough so the chain doesn't rub.
03-27-08, 08:55 PM
Unless its rubbing really badly, I'd leave it alone. If you let out the limit screw further, you risk dropping the chain off the ring when you shift down to the 39
03-27-08, 10:41 PM
Um, from the picture that's *not* the cross-chain combo. He seems to be having trouble with small front/large rear, and that combo should be usable.
Easy to fix, just adjust the indexing for the front derailer. The indexing adjuster is usually a barrel knob near the shifter. To properly adjust it, you may need to back off on the lower limit screw if it's been set particularly zealously, but that may not be necessary.
Now if you get rub with the big/big or small/small combo, that is cross chaining and is a combo that shouldn't generally be used.
03-27-08, 10:53 PM
The small ring is the cable slack position so I'd have to respectfully say that it'll be due more to the limit screw than the cable adjuster. But it's worth checking both to be sure.
03-28-08, 12:20 AM
I'd say limit screw, and maybe too much cable tension (that can be solved by turning the barrel adjuster clockwise)
03-28-08, 04:18 AM
Can too much cable tension cause rubbing? I have something of a similar problem on my bike and my cable is as tight as it can go.
03-28-08, 05:21 AM
there are many pages that discuss der.adjustment.Do a search and find the easiest one to try.You really cant screw anything up.
03-28-08, 06:01 AM
Loosen the low limit screw a quarter turn.
Small/big isn't a cross chain position.
03-28-08, 06:13 AM
Thank you all. I really appreciate the explanations. I tinkered with it last night, but still have to make some more adjustments to make.
03-28-08, 07:47 AM
Good luck. It's not too tough, you just need to put the bike in that small/big combo and adjust the FD until it just barely doesn't rub that plate. As mentioned before, it's either the barrel adjuster or the limit screw. Try the park tool site for a good explanation.
As others have said, that is not a cross-chain combination. As you've said it is 1st gear (or low gear).
When in this gear combination if the cable has much tension then try adjust the cable to have less tension and see if this moves the derailleur toward the frame enough to eliminate the chainrub. The cable adjustment is probably a barrel adjuster found on the left side of the downtube.
If relaxing the tension does not move the derailleur in then try adjusting the low limit screw.
Good instructions for adjusting derailleurs can be found at http://www.parktool.com. Do each step in proper sequence leaving nothing out.
Good looking bike.
Check with a local LBS to see if they offer the Park Tool Mechanics course. It's a 3 session course that will cover exactly this sort of stuff. Well worth the cost.
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