# Chain rubs inner front derailleur cage when on lowest gear.



## WK95 (Feb 4, 2014)

I recently replaced my bottom bracket and crankset and while tuning my bike up, I noticed that when the chain is on the lowest possible gear (biggest cog and smallest chainring), the chain rubs the inner part of the front derailleur.

The chain line for the crankset is 45mm and the front derailleur is also for 45 mm. The front derialleur

Both the front derailleur and the crankset are Shimano Soras but the front derailleur is front the last gen. one. However, seeing as the chainline is the same at 45 mm, they should both be compatible.

As for the limit screw, I've loosened it all the way but the problem still persists.

I'm thinking that I might possibly need bottom bracket spacers.

I'll try to measure my chainline later.


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## cxwrench (Nov 9, 2004)

Have you bothered undoing the cable so the derailleur can move when you adjust the limit screw? You should definitely not need any spacers.


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## WK95 (Feb 4, 2014)

I loosened the cable when adjusting the limit screw which is practically at its loosest.

Also, this is teh same front derailleur that came with my bike. I just noticed that with the lower limit screw at it's lowest, the front derailleur will hit the frame when I shift down.

I always heard this metal-on-metal sound of the front derailleur hitting the frame but never noticed that it came from the front derailleur until recently. I;m pretty sure this is abnormal.

So now I have two problems
1) when the chain is in lowest possible gear, it rubs the inside (the part side closest to the frame) of the front derailleur cage
2) when I shift down and the low limit screw is at it's loosest, the front derailleur makes an audible clank when it hits the frame shifting down.


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## Camilo (Jun 23, 2007)

Start from scratch and install and adjust the front derailleur exactly according to Shimano's instructions. Each and every step, carefully, don't skip any step even though you think you can.


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## Roland44 (Mar 21, 2013)

Camilo said:


> Start from scratch and install and adjust the front derailleur exactly according to Shimano's instructions. Each and every step, carefully, don't skip any step even though you think you can.


Great advice here. Follow the instractions to the letter OP and I am sure everything will work just fine. Shimano has some pretty detailed instruction documentation, check it out.


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## Peter P. (Dec 30, 2006)

Following the installation instructions on the Shimano web site is a good start. Your derailleur's model number can be found on the back of the inner cage or on the inside of the clamp.

I've found raising the cage 1-3mm higher above the teeth than even the Shimano tech docs recommend can sometimes cure your problem. Aligning the face of the outer cage plate with the plane of the large ring usually gives the best shifting performance and is easy to set. But sometimes, angling the tail end of the derailleur cage just a smidge inward will cure your problem.

Are you sure you haven't mixed a triple length BB with a double crank? Is the front derailleur compatible with the crank i.e., compact vs. standard?

Lastly, sometimes I've cured the problem by gently bending the inner cage so it clears the chain at the rub spot. This was common practice with pre-index shifting era front derailleurs. Today's indexed shifting front derailleurs are fussier, but I've had luck with this approach, too.

Alternatively, you can angle the tail of the cage toward the rear wheel just until the inner cage clears the large cog. Then bend the outer cage as needed to provide clearance on the large ring. I've done this as well. You basically place a screwdriver between the outside of the large ring and the inside of the outer cage plate and flex the outer cage plate until it bulges out slightly. If you don't like your tweeks, you can always return the cage shape to it's former straight-it's steel so it can take a lot of bending.


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## cxwrench (Nov 9, 2004)

Is the derailleur a 'top swing' meaning the cage pivots above the clamp that holds it on the seat tube rather than pivoting below it? If so, that's part of the problem. On many inexpensive bikes the top swing derailleur cannot physically move far enough to clear the chain in low gear. The only real fix is to replace that derailleur w/ a bottom swing derailleur.


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## WK95 (Feb 4, 2014)

I'm not sure about top or bottom swing but my front derailleur is bottom pull and I assume that's related.

Specifically, my FD is a Shimano FD-2303. I found the instructions so I'll try to "reinstall" it tomorrow.
Here is an image









Please disregard the second image. I cant remove it.


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## WK95 (Feb 4, 2014)

Peter P. said:


> Following the installation instructions on the Shimano web site is a good start. Your derailleur's model number can be found on the back of the inner cage or on the inside of the clamp.
> 
> I've found raising the cage 1-3mm higher above the teeth than even the Shimano tech docs recommend can sometimes cure your problem. Aligning the face of the outer cage plate with the plane of the large ring usually gives the best shifting performance and is easy to set. But sometimes, angling the tail end of the derailleur cage just a smidge inward will cure your problem.
> 
> ...


My original and current crank were both triples.


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## Camilo (Jun 23, 2007)

Camilo said:


> Start from scratch and install and adjust the front derailleur exactly according to Shimano's instructions. Each and every step, carefully, don't skip any step even though you think you can.





Roland44 said:


> Great advice here. Follow the instractions to the letter OP and I am sure everything will work just fine. Shimano has some pretty detailed instruction documentation, check it out.





Peter P. said:


> Following the installation instructions on the Shimano web site is a good start. Your derailleur's model number can be found on the back of the inner cage or on the inside of the clamp.
> 
> I've found raising the cage 1-3mm higher above the teeth than even the Shimano tech docs recommend can sometimes cure your problem. Aligning the face of the outer cage plate with the plane of the large ring usually gives the best shifting performance and is easy to set. *But sometimes, angling the tail end of the derailleur cage just a smidge inward will cure your problem.*....


I wanted to emphasize the advice to not be afraid to tweak the angle a little. I still hold to following the steps from A to Z exactly without skipping steps. There's a lot of interaction among the steps and there's logic (that you might not understand off hand) to the order of the steps.

One of the steps commonly directs you to align the derailleur cage parallel to the chain ring. This makes sense in theory, but in my personal experience, it is tough in practice. Lighting, eyesight, the contours of the derailleur cage all make it impossible for me to state with certainty that I have aligned it perfectly. So, After I do the best I can, I get the shifting as good as I can and then carefully analyze what is not exactly right. Most of the time, it's the angle of the cage. I've either misaligned it by eye, or it just needs to be tweaked. It doesn't matter what the reason, the solution is the same, usually just angling it a tiny bit inward (either inward from parallel or inward from the non-parallel position I _thought_ was parallel.. again it doesn't matter!).


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