Chain rubbing on front derailler when on high rear gear
#1
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Chain rubbing on front derailler when on high rear gear
Hello all, I'm sorry for what is probably a really simple problem but I'm new to bikes in general and cannot find any answers online or get my head around a lot of the terms.
I've just bought an old Fuji Suncrest with Deore gears. The guy I bought it from replaced the rear gear cable as it was old apparently, but I'm having some issues with the front gear. Sometimes I cannot shift onto the largest front cog (which I suspect has something to do with which rear gear I am in), and after experimenting a bit at home I've found that when the rear gears are on the smallest cogs, and when I do have the chain on the largest front cog, the chain rubs on the outer edge of the front derailleur.
I've tried adjusting the two screws (L and H?) but I notice no noticeable movement of the derailleur either way. I'm wondering if this means something is wrong with the gear, the cable is loose, old, or if the entire thing needs a tune-up (I can't bring it to a shop until the weekend as I need it to commute).
Any help would be much appreciated, and if anyone can suggest some things to try I would be happy to. Thanks.
I've just bought an old Fuji Suncrest with Deore gears. The guy I bought it from replaced the rear gear cable as it was old apparently, but I'm having some issues with the front gear. Sometimes I cannot shift onto the largest front cog (which I suspect has something to do with which rear gear I am in), and after experimenting a bit at home I've found that when the rear gears are on the smallest cogs, and when I do have the chain on the largest front cog, the chain rubs on the outer edge of the front derailleur.
I've tried adjusting the two screws (L and H?) but I notice no noticeable movement of the derailleur either way. I'm wondering if this means something is wrong with the gear, the cable is loose, old, or if the entire thing needs a tune-up (I can't bring it to a shop until the weekend as I need it to commute).
Any help would be much appreciated, and if anyone can suggest some things to try I would be happy to. Thanks.
#2
Mechanic/Tourist
If you can't get your head around the terms that may be a problem, as we will use the same terms, but here goes.
First Google adjust front derailleur and go first to the sheldonbrown.com and parktool.com/blog results. Study those, then use Youtube to see the process. Note that the first step is to position the derailleur properly (rotation and height above large chainwheel, so do not skip that.
Secondly, it is the H screw (HIGH) you need to adjust, but you need to pull on the lever/cable to get changes you've made to the H/L limit screws - they have no effect until the derailleur contacts them. You will see what I mean once you check the instructions and video.
Finally, the cable needs to be in good shape to shift properly, so that could be part of your problem. A bent derailleur or worn pivots will complicate things.
It's best to get in-person help when you are this new to things, especially with a bike that may have other needs, including safety related ones. Check locally (helps to know what city you are in) for bike co-ops or shops that offer repair clinics, or simply for a knowledgeable friend.
First Google adjust front derailleur and go first to the sheldonbrown.com and parktool.com/blog results. Study those, then use Youtube to see the process. Note that the first step is to position the derailleur properly (rotation and height above large chainwheel, so do not skip that.
Secondly, it is the H screw (HIGH) you need to adjust, but you need to pull on the lever/cable to get changes you've made to the H/L limit screws - they have no effect until the derailleur contacts them. You will see what I mean once you check the instructions and video.
Finally, the cable needs to be in good shape to shift properly, so that could be part of your problem. A bent derailleur or worn pivots will complicate things.
It's best to get in-person help when you are this new to things, especially with a bike that may have other needs, including safety related ones. Check locally (helps to know what city you are in) for bike co-ops or shops that offer repair clinics, or simply for a knowledgeable friend.
Last edited by cny-bikeman; 10-15-13 at 01:33 PM.
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It sounds like the front shift cable has stretched, that's all. It's not pulling fully onto the top crank position.
You should probably replace the cable. But, you should totally be able to tighten it up a smidge and keep riding it.
1) shift the front derailer to the smallest crank.
2) adjust the L screw until the front derailer cage is visibly centered over the small crank
3) loosen the cable clamp bolt on the front derailer
4) pull the cable taut and re-tighten the cable clamp
5) shift through the cranks. warning: the derailer may now travel enough to drive the chain right off the top crank.
6) shift to the biggest crank and smallest rear cog
7) adjust the H screw until the front derailer cage rubs on the chain. Then back it off a half turn or so.
8) RIDE, RIDE, RIDE!
Park Tool's website has all the info you need: https://www.parktool.com/blog/repair-...ur-adjustments
You should probably replace the cable. But, you should totally be able to tighten it up a smidge and keep riding it.
1) shift the front derailer to the smallest crank.
2) adjust the L screw until the front derailer cage is visibly centered over the small crank
3) loosen the cable clamp bolt on the front derailer
4) pull the cable taut and re-tighten the cable clamp
5) shift through the cranks. warning: the derailer may now travel enough to drive the chain right off the top crank.
6) shift to the biggest crank and smallest rear cog
7) adjust the H screw until the front derailer cage rubs on the chain. Then back it off a half turn or so.
8) RIDE, RIDE, RIDE!
Park Tool's website has all the info you need: https://www.parktool.com/blog/repair-...ur-adjustments
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Thanks to both of you. I tried what you suggested cny_bikeman, and simply pulled a bit on the cable/gear lever, I noticed that the derailler moved outward a bit and was in a much more logical progression, so I imagine it's exactly what tim said, a stretched cable (just the reason the guy replaced the rear gear cable too). This weekend I'll diligently go through the texts you guys gave and try adjusting it myself. Thanks again!
Edit: A massive thanks! I just followed your steps Tim and on the second try managed to tighten the cable enough and adjust the screws well enough to fix the entire problem. The bike changes gears perfectly now, I'm very happy!
Edit: A massive thanks! I just followed your steps Tim and on the second try managed to tighten the cable enough and adjust the screws well enough to fix the entire problem. The bike changes gears perfectly now, I'm very happy!
Last edited by JPeters; 10-15-13 at 02:41 PM.
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Knowing that you got an old bike back on the road--and got a smile on your face by doing so--is thanks enough. Many old bikes have great components, and just need a good tune up.
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harisund
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