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Old 07-02-11, 01:26 PM   #1
thyway
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An unusually sinister front derailleur chain rub

I'm about to set off on a touring trip in a foreign country, and have bought a cheap but capable bike for the adventure at hand. Unfortunately, when I received the assembled bike, the FD couldn't even manage to move the chain to the highest chain ring. However, after reading up on Sheldon's, Park tools and various youtube guides, I did the following;

I have...
-aligned the FD properly
-Adjusted the height of the FD relative to the high ring wheel
-released the FD wire anchor bolt and tightened the slack as much as possible.
-further tightened the wire through the barrel adjuster
-Maxed out the H&L limit stops
+(I began by adjusting the RD which works like a charm)

This helped me reach the 3rd chain ring, but some problems still remain; while avoiding any cross-shifting, it is still impossible to shift to either lowest or highest cogs without the chain rubbing against the FD. (If I'm running on the 1st chain I can only go up to the 2nd cog, and if I'm running on the 3rd chain ring, I can only go to the 6th cog). I've found that this is the "ideal point" and that any further adjustment of the inner wire tension only leads to a trade off on either high/low rub.
It seems as if the "cage" isn't moving enough sideways to accompany both the extremes at any given setting.

Is there anything else I could do, or should I just accept that I wont be able to use the full potential of this bike?
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Old 07-02-11, 01:39 PM   #2
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OK, if I reading you correctly the chain still rubs on the outside of the cage, on the outer chainring and outermost rear sprocket. If so, your cage needs to be trimmed outboard a bit more. The issue could be either the outer limit or cable adjustment.

Eliminate the outer limit by drawing the bare wire away from the frame at the downtube (or toptube) like a bow string and seeing if the cage moves out more.

If yes, then you need to shorten (tighten) the wire a bit hopefully using an adjuster either on the frame stop, lever, or inline on the housing. (if you don't have an adjuster, I suggest buying and adding an inline one to make future setup and adjustment easier).

If you cannot move the cage out more by the bowstring method, then backing off the limit a hair will help, but be aware that doing so doesn't actually move the cage out, it only allows it to move out. You'll now (probably) need to adjust the cable length to take advantage of the change.
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Old 07-02-11, 02:19 PM   #3
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Quote:
Originally Posted by thyway View Post
I'm about to set off on a touring trip in a foreign country, and have bought a cheap but capable bike for the adventure at hand. Unfortunately, when I received the assembled bike, the FD couldn't even manage to move the chain to the highest chain ring. However, after reading up on Sheldon's, Park tools and various youtube guides, I did the following;

I have...
-aligned the FD properly
-Adjusted the height of the FD relative to the high ring wheel
-released the FD wire anchor bolt and tightened the slack as much as possible.
-further tightened the wire through the barrel adjuster
-Maxed out the H&L limit stops
+(I began by adjusting the RD which works like a charm)

This helped me reach the 3rd chain ring, but some problems still remain; while avoiding any cross-shifting, it is still impossible to shift to either lowest or highest cogs without the chain rubbing against the FD. (If I'm running on the 1st chain I can only go up to the 2nd cog, and if I'm running on the 3rd chain ring, I can only go to the 6th cog). I've found that this is the "ideal point" and that any further adjustment of the inner wire tension only leads to a trade off on either high/low rub.
It seems as if the "cage" isn't moving enough sideways to accompany both the extremes at any given setting.

Is there anything else I could do, or should I just accept that I wont be able to use the full potential of this bike?
1. That's normal if you're talking about the cross-chained combinations (biggest ring and biggest cog, smallest ring and smallest cog - people don't really refer to them as 1, 2, and 3 to avoid the ambiguity)
2. Some shifters allow the front derailleur to be trimmed to intermediate positions to avoid it (although you still want to avoid cross-chained combinations due to increased noise and chain wear)
3. You might be able to do a little better without trim by rotating the cage a bit.
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Old 07-02-11, 05:17 PM   #4
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Be sure it's the chain rubbing on the derailleur cage and not the inner plate of the derailleur cage rubbing on the middle chainring.
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Old 07-02-11, 07:25 PM   #5
thyway
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Thanks for the quick replies! I will clarify the issue a bit:
-I'm not running on cross chained gears, it rubs against the inside (left) of the cage when I run on the innermost ring + innermost cog AND the outside (right) of the cage when I run on the outermost ring + outermost cog.
Therefore I assume that tightening the wire to remove the rub when on the outermost ring and cog would only worsen the rub when running on the innermost ring and cog (and the opposite I when loosening the wire).

-I can visually confirm the chain rubbing against the cage in both cases, but I will take a look on the middle ring to make sure that the cage is not rubbing against it.

+In case anyone has particular experience of this derailleur, it's a 3x7=21 speed setup with a Shimano Tourney FD and Shimano TZ BD.
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Old 07-02-11, 09:00 PM   #6
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I had a bike with the same FD and RD and two bike shops were not
able to resolve the problem. They decided the shifters were not
moving the derailleurs properly. The notches were wrong.

I returned the bike.

On the FD, if you loosen both limit screws a little and tighen
the cable some more it will work but you won't be able to
use but five cogs on the center chaining and three on each
end with the large and small chaining.

I rode the bike a few days and gave it back to them.
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Old 07-02-11, 09:59 PM   #7
thyway
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Oh, that's bad news! But I'm really grateful to know that there's a real underlying problem and not just me screwing some settings up. No wonder I've been pulling my hair over this.
As I ordered the bike from a Korean internet mall who then probably sent the parts to a separate shop for assembly before delivering it to me, I fear that returning the bike might not be an option.

Does anyone have any other ideas or experiences that can turn this unfortunate situation around?
If not, is it worth looking into replacing the derailleurs/shifters? (apart from the stated problem, the bike feels nice). The bike cost me roughly $150, which is very cheap compared to what I'm used to, would it be madness to invest in a new set for it?
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Old 07-03-11, 08:50 AM   #8
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Check the width of the FD, I thought about trying to spread it out a little,
but since it was a new bike I didn't. Can you go to a bike shop and check
the width of a new, or different one maybe??
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