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Problem with front deraileur

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alexwang32 Offline
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Posts: 5
Joined: May 2014
Post: #1
Problem with front deraileur
Hello, I have a mountain bike with three chain rings in the front. The chain rubs on the derailleur's inner cage when I am using the lowest gear ( smallest front, largest back gear), and rubs on the outer cage when I am using the highest gear ( largest front, smallest back gear).

Now, I've tried loosening both limit screws, but when I loosen them I feel no resistance at all, in fact even if I completely unscrew them out the chain is still rubbing. I tried the barrel adjuster but that didn't work, besides even if it did it would only be able to fix one side of the chain ring.

It's a new bike and the derailleur seems to be parallel to the big chain ring. I really need to use the lowest gear a lot so if I have to sacrifice the highest gear I would do so. Please help!
May 11, 2014 09:42 AM
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nfmisso Offline
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San Jose, CA
Posts: 2,332
Joined: Jul 2010
Post: #2
RE: Problem with front deraileur
Small-Small and Large-Large are NOT recommended, these combinations are called cross-chaining which leads to excessive wear on the chain, derailleurs freewheel (or cassette) and cranks. Neither small-small or large-large offer unique gear ratios. And the chain will always rub in small-small, if not the front derailleur, then the large chain ring.

The lowest gear on the bike is small at the front, large at the rear. The lowest gear is the one in which pedaling is the easiest, and you go the least distance per crank rotation. The highest gear on the bike is larger front, small rear; it is the hardest to pedal and provides the most distance per revolution of the crank.

Typically, on the small chain ring at the front, you should use the only the largest three or four cogs at the back, on the largest chain ring at the front only the smallest four or five cogs, and the middle ring all of the cogs at the back.

Your messing with the adjustments without understanding what they do has probably caused problems. You will need to find someone with skill to fix the damage.

Nigel
May 11, 2014 12:41 PM
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DaveM Offline
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Posts: 1,398
Joined: Aug 2008
Post: #3
RE: Problem with front deraileur
I suspect the cable tension is too high. That would explain the rubbing in lowest gear even when you back out the limit screw. If the tension is high enough, you may not be getting the shifter all the way up to the highest click when you're trying to get into the high gear.

Sounds like you checked the alignment of the der. Also check to make sure it isn't too high above the chainrings. You don't want more than a couple mm gap. It could cause rubbing if it's very high.

Unfortunately, hard to diagnose this for sure remotely. You need to step through the full adjustment process and you should find what is causing the issue. Good luck.
May 11, 2014 06:38 PM
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cny-man Offline
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Syracuse, NY
Posts: 393
Joined: Jul 2012
Post: #4
RE: Problem with front deraileur
FIRST step is to make sure the front derailleur is correctly positioned, then set limit screws - inner with no cable tension or with it disconnected, outer by pulling on the cable like a bow string after shifting to the largest chainwheel to make sure it clears without going too far. Google "adjust front derailleur" go first to parktool.com/blog and Sheldonbrown.com. Only after you study those should you rely on videos, which often leave out important info.
May 12, 2014 10:31 AM
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alexwang32 Offline
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Posts: 5
Joined: May 2014
Post: #5
RE: Problem with front deraileur
(May 11, 2014 06:38 PM)DaveM Wrote:  I suspect the cable tension is too high. That would explain the rubbing in lowest gear even when you back out the limit screw. If the tension is high enough, you may not be getting the shifter all the way up to the highest click when you're trying to get into the high gear.

Sounds like you checked the alignment of the der. Also check to make sure it isn't too high above the chainrings. You don't want more than a couple mm gap. It could cause rubbing if it's very high.

Unfortunately, hard to diagnose this for sure remotely. You need to step through the full adjustment process and you should find what is causing the issue. Good luck.

I suspected the height of the front derailleur may need adjustment. It's currently more than 1.5mm above the big chain ring. Perhaps I should lower it.

The cable tension seems to be fine... there is some slack when it's on the small chain ring as far as I can see, but maybe if I loosen the cable a bit more it would help. But then, already I find it hard to shift to the upper chain rings ( I need to pedal really fast and let the pedals spins freely in order to get the chain to shift up a gear ), if I loosen the cable even more I probably will have more problem. Perhaps I'll try adjusting the derailleur height first.
May 16, 2014 08:09 AM
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cny-man Offline
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Syracuse, NY
Posts: 393
Joined: Jul 2012
Post: #6
RE: Problem with front deraileur
(May 16, 2014 08:09 AM)alexwang32 Wrote:  I suspected the height of the front derailleur may need adjustment. It's currently more than 1.5mm above the big chain ring. Perhaps I should lower it.

The cable tension seems to be fine... there is some slack when it's on the small chain ring as far as I can see, but maybe if I loosen the cable a bit more it would help. But then, already I find it hard to shift to the upper chain rings ( I need to pedal really fast and let the pedals spins freely in order to get the chain to shift up a gear ), if I loosen the cable even more I probably will have more problem. Perhaps I'll try adjusting the derailleur height first.

Not "perhaps" on the height - as I noted the derailleur needs to be properly positioned before adjusting. Also no "maybe" on cable tension - it does not affect inner adjustment, and reducing tension would worsen the problem rubbing on the outer cage. One needs to observe carefully, think logically, and proceed carefully when working on a bike. Again, position it, adjust the limits, then cable tension. If the problem remains there is something more than adjustment in play, and you may need in-person assistance.

Also, I neglected to mention before that if a new bike and purchased from a local store you should take it back for free adjustment.
May 16, 2014 08:52 AM
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alexwang32 Offline
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Posts: 5
Joined: May 2014
Post: #7
RE: Problem with front deraileur
I thought when adjusting bikes you have to go with try and error. I really want to DIY this. I've watched plenty of videos and read a couple of pages of a bike assembly manual ( I found it at the library ), so I think I can nail it.

I took my bike in the store for adjustments once, the front disk break was rubbing on the caliber pad, but now I've taken my bike to our cottage 200km away so... I want to ride this summer and not let it sit in the garage.

Thanks for the help.
May 18, 2014 08:59 AM
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nfmisso Offline
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San Jose, CA
Posts: 2,332
Joined: Jul 2010
Post: #8
RE: Problem with front deraileur
(May 18, 2014 08:59 AM)alexwang32 Wrote:  I thought when adjusting bikes you have to go with try and error. ......

NEVER !!! Bicycles require a systematic approach, as our friend from NY outlined. Trial and error will not work.

Nigel
May 18, 2014 09:26 AM
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alexwang32 Offline
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Posts: 5
Joined: May 2014
Post: #9
RE: Problem with front deraileur
I am following instructions I got from different sources, therefore I'm not blindly adjusting this and that. I have already fixed my rear wheel rubbing problem by watching a youtube video. The reason I'm asking you guys is that the front derailleur is relatively complex, it's hard to find a correct remedy.
May 18, 2014 07:03 PM
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cny-man Offline
Senior Member

Syracuse, NY
Posts: 393
Joined: Jul 2012
Post: #10
RE: Problem with front deraileur
You asked for help, and we're trying to give it. Videos often give incomplete info, which is why I suggested parktool.com and sheldonbrown.com as the first references. If you are unable to take the bike back to where you bought it you needed to read and follow the full procedure on one of those sites.

If you position the derailleur correctly and properly adjust the inner and outer limits so that the chain clears the cage when the cable is not involved, and you get rubbing when using the cable and levers, then there's a problem with one of those. If you are unable to eliminate the rubbing by adjusting the limits then there is a problem other than routine adjustment, and you need some in-person help. Perhaps a more knowledgeable friend. If that option is not available either then we need some clear pics of the derailleur in the inner and/or outer adjustment positions from the side, top and back.

It's a logical process, and although it involves several adjustments it's not trial and error or luck that determines whether the derailleur can be adjusted.
May 18, 2014 08:35 PM
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alexwang32 Offline
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Posts: 5
Joined: May 2014
Post: #11
RE: Problem with front deraileur
(May 18, 2014 08:35 PM)cny-man Wrote:  You asked for help, and we're trying to give it. Videos often give incomplete info, which is why I suggested parktool.com and sheldonbrown.com as the first references. If you are unable to take the bike back to where you bought it you needed to read and follow the full procedure on one of those sites.

If you position the derailleur correctly and properly adjust the inner and outer limits so that the chain clears the cage when the cable is not involved, and you get rubbing when using the cable and levers, then there's a problem with one of those. If you are unable to eliminate the rubbing by adjusting the limits then there is a problem other than routine adjustment, and you need some in-person help. Perhaps a more knowledgeable friend. If that option is not available either then we need some clear pics of the derailleur in the inner and/or outer adjustment positions from the side, top and back.

It's a logical process, and although it involves several adjustments it's not trial and error or luck that determines whether the derailleur can be adjusted.

Ok thanks I'll do what you said and post back the results.
May 20, 2014 04:28 AM
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