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Discussion Starter · #1 ·
Been reading Zinn and the Art of Mountain Bike Maintenance and trying to learn how to adjust my own derailleurs.

I am having a problem now when I am riding in my middle ring up front and largest (or next to largest) cog in the back. My chain randomly drops from the middle ring to the little ring. I know I probably shouldn't be riding in this combination anyway, but ...

How do you keep the chain from dropping down to the the little ring up front? I am not shifiting or anything it just drops by itself.

I followed the instructions for setting the limit screws on the front derailleur. This seemed to help keep the chain from dropping off the little ring onto the frame. I don't see any suggestions though for the chain dropping from middle to the little ring.

Thanks
 

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You should be making the same adjustments to keep the chain from droppingfrom the middle ring to the small ring as you would keeping it dropping off the small ring. Read up at the Park website and see if that helps.
 

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You may want to try increasing the cable tension a little bit, that would pull your fd outwards and it may work. Just turn the barrel adjuster on the shifter about 1/4 of a turn at a time, and see if it helps. With the limit screws, you should set the fd so the chain doesn't rub on the cage when in the little ring (about a mm of clearance) and then that it doesn't rub on the big ring (again a mm clearance) the rest you should adjust with cable tension. Also, check to make sure that the fd cage is aligned properly with the chainrings (you can eyeball it from the top and see if it is way off line) and while you are at it, check for vertical alignment, the bottom of the cage should be about 2mm from the top of the rings. The Park site has very clear instructions.
And since you say that it happens randomly, I would recommend that you make sure your midle ring is not bent.
 

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Sounds like chainline or bent ring

You should be able to access all of your rear cassette from your middle ring without any front derailleur rub. If your chainline is off a little it might pull the chain off the middle ring down to the small ring, chainline is controlled by the spindle length on your bottom bracket. A bent ring might cause the chain to fall to the inside also. Or you might have the front derailleur adjusted too far toward the small ring, does the chain rub the front derailleur when you are in the smaller cogs, and maybe a little when you are in the middle cogs?
 

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Discussion Starter · #5 ·
StormShadow said:
You should be making the same adjustments to keep the chain from droppingfrom the middle ring to the small ring as you would keeping it dropping off the small ring. Read up at the Park website and see if that helps.
I will print this out and give these directions a try. Thanks for your help.
 

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Discussion Starter · #6 ·
FrozenK said:
You may want to try increasing the cable tension a little bit, that would pull your fd outwards and it may work. Just turn the barrel adjuster on the shifter about 1/4 of a turn at a time, and see if it helps. With the limit screws, you should set the fd so the chain doesn't rub on the cage when in the little ring (about a mm of clearance) and then that it doesn't rub on the big ring (again a mm clearance) the rest you should adjust with cable tension. Also, check to make sure that the fd cage is aligned properly with the chainrings (you can eyeball it from the top and see if it is way off line) and while you are at it, check for vertical alignment, the bottom of the cage should be about 2mm from the top of the rings. The Park site has very clear instructions.
And since you say that it happens randomly, I would recommend that you make sure your midle ring is not bent.
I will check the clearances, and play around with the cable tension some more. The last time I adjusted the derailleur, I tried to put the maximum amount of tension on the cable that would still allow me to shift between the rings.

Any good way to make sure the middle ring is not bent? I was thinking I could take it off then lay it on something flat.
 

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Discussion Starter · #7 ·
liatdraH said:
You should be able to access all of your rear cassette from your middle ring without any front derailleur rub. If your chainline is off a little it might pull the chain off the middle ring down to the small ring, chainline is controlled by the spindle length on your bottom bracket. A bent ring might cause the chain to fall to the inside also. Or you might have the front derailleur adjusted too far toward the small ring, does the chain rub the front derailleur when you are in the smaller cogs, and maybe a little when you are in the middle cogs?
I have heard people talking about chainline but I never understood what is was or how to determine if it is off. I will do some more research on that. Thanks.

I think it only rubs when I am on the big ring and big cog or the little ring and little cog.
 

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FrozenK said:
You may want to try increasing the cable tension a little bit, that would pull your fd outwards and it may work. Just turn the barrel adjuster on the shifter about 1/4 of a turn at a time, and see if it helps. With the limit screws, you should set the fd so the chain doesn't rub on the cage when in the little ring (about a mm of clearance) and then that it doesn't rub on the big ring (again a mm clearance) the rest you should adjust with cable tension. Also, check to make sure that the fd cage is aligned properly with the chainrings (you can eyeball it from the top and see if it is way off line) and while you are at it, check for vertical alignment, the bottom of the cage should be about 2mm from the top of the rings. The Park site has very clear instructions.
And since you say that it happens randomly, I would recommend that you make sure your midle ring is not bent.
This one is good advice. What has worked for me is setting the high and low while the chain is in its maximum high or low position. big ring up front on small ring back for high stop and small front with large back for low stop. Then shift to the middle and use your barrel adjuster to fine tune the middle ring. Also I am no expert but I like to ride with the rear casset in a mid range gear say 4 or 5 and then just do my gear selections with the front chainring. That way I almost always have an exceptable chainline without haveing to think about it to much. http://www.parktool.com
 
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