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Chain rubbing front derailleur cage issue
#1
It seems like I can spend hours working the front shifter trim control and still not completely avoid chain rubbing problems. Specifically, my issue seems to be with the middle chainring.

Here's a quick rundown of my drivetrain:

Chainwheels -- SR Suntour XCT-V2, 48/38/28T
Front derailleur -- Shimano FD-C051
Rear freewhee; -- Shimano MF-TZ31, 14/16/18/20/22/24/34T 7-speed
Rear derailleur -- Shimano RD-M310

I know to avoid small chainring/small sprocket combinations such as 1/5, 1/6, 1/7, and large/large combinations such as 3/1, 3/2, and 3/3. That's not an issue. I would like to be able to use all rear sprockets with the middle chainring, but no matter where I set the trim, it seems I'm always getting a rub on one side or the other.

I can trim it outward enough so that 2/7 doesn't rub, but then 2/1 will definitely rub, and usually so does 2/2. If I then move the trim control the other way, just enough to stop 2/2 from rubbing, 2/7 seems to cause a rub. I'm not so worried about 2/1, as my 2/1 and 1/2 gear ratios are reasonably close and I probably should hit the granny chainring if 2/2 isn't enough to climb, but I'm annoyed that I can't seem to get the whole range from 2/2 to 2/7 without the chain rubbing the front derailleur somewhere.

Since trimming and cable adjustments don't seem to be helping this, do you all suppose it could be a position issue (derailleur height/angle)? It doesn't look that bad, honestly; I can say for sure that the cage clears the large chainring by probably 2-3mm, and the angle looks like it's parallel to the frame.

Or would I be better off with a front derailleur with a wider cage?
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#2
I'm still somewhat new at this whole cycling thing, BUT... I had a similar issue with my set up (triple front, 7-speed rear, 2010 specialized road bike). The height was my first issue, and once that was figured out, the cable tension had to be readjusted from scratch. I'd recommend you investigate the height thing further than just my advice. If others confirm, lower the front derailleur height by like (literally) 1/16th to 1/8th of an inch. Then go through the process of setting your cable tension. There is a video on bicycletutor for this.

Ryan
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#3
I have that problem too!! It's driving me nuts!!!
I thought about a wider mech. But why supply a bike with 7 gears and a mech that doesn't work with it!!!!
But then a wider cage might mean it doesn't change cogs as easy????
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#4
Height of the front derailleur should be 2mm over the biggest chainring...
  Reply
#5
(08-30-2010, 07:46 AM)Larry H Wrote:  It seems like I can spend hours working the front shifter trim control and still not completely avoid chain rubbing problems. Specifically, my issue seems to be with the middle chainring.

Here's a quick rundown of my drivetrain:

Chainwheels -- SR Suntour XCT-V2, 48/38/28T
Front derailleur -- Shimano FD-C051
Rear freewhee; -- Shimano MF-TZ31, 14/16/18/20/22/24/34T 7-speed
Rear derailleur -- Shimano RD-M310

I know to avoid small chainring/small sprocket combinations such as 1/5, 1/6, 1/7, and large/large combinations such as 3/1, 3/2, and 3/3. That's not an issue. I would like to be able to use all rear sprockets with the middle chainring, but no matter where I set the trim, it seems I'm always getting a rub on one side or the other.

I can trim it outward enough so that 2/7 doesn't rub, but then 2/1 will definitely rub, and usually so does 2/2. If I then move the trim control the other way, just enough to stop 2/2 from rubbing, 2/7 seems to cause a rub. I'm not so worried about 2/1, as my 2/1 and 1/2 gear ratios are reasonably close and I probably should hit the granny chainring if 2/2 isn't enough to climb, but I'm annoyed that I can't seem to get the whole range from 2/2 to 2/7 without the chain rubbing the front derailleur somewhere.

Since trimming and cable adjustments don't seem to be helping this, do you all suppose it could be a position issue (derailleur height/angle)? It doesn't look that bad, honestly; I can say for sure that the cage clears the large chainring by probably 2-3mm, and the angle looks like it's parallel to the frame.

Or would I be better off with a front derailleur with a wider cage?

You absolutely have to adjust the front derailleur to different positions for even using just the center chainring. For example (using your nomenclature) 2/1-2/3 will be one shifter adjustment point, 2/3-2/5 will be another and 2/5-2/7 a third. This is the nature of front derailleurs.
Nigel
  Reply
#6
sounds like height and /or alignment, this is the set up guide for your FD, but are you sure the inner or outer plate is not bent.

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Tourney/FrontDriveSystem/SI_6DK0B/SI_6DK0A/SI_6DK0B_En_v1_m56577569830607106.pdf

another thought, are you using a compatible shifter?
  Reply


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