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Old 05-21-09, 11:03 AM   #1
fadetoblack6902 
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weird front derailleur issue

I have a Fuji Finest with sora components, triple crank. When in the small or middle chainring and the smallest 2 or 3 cogs, the chain rubs on the front derailleurs outer cage plate. Also when in those gear combinations if you spin backwards the chain jumps badly. In any other gear combination it runs perfectly. It shifts perfect. Obvious solution is more cable tension, but it is already at its limit. If you put any more tension on it it tries to jump to the next gear.

The derailleur is set up correctly. Outer plate is parallel with chain, tension is correct, limit screws are correct, outer cage is 2mm above chainring.

any ideas?

Thanks in advance
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Old 05-21-09, 11:25 AM   #2
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Solution:

Don't crosschain.
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Old 05-21-09, 11:44 AM   #3
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Solution:

Don't crosschain.
this
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Old 05-21-09, 11:44 AM   #4
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Yes I know not to crosschain, but the 3rd smallest cog in the middle chainring isnt exactly cross chaining. Most bikes when in good adjustment won't have this problem in the middle ring until the smallest cog or maybe 2nd smallest.
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Old 05-21-09, 11:50 AM   #5
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Middle chainring to small cog is not cross-chaining, you dopes.

The only way I've found to troubleshoot triple front derailleurs successfully and without too much profanity is to completely reinstall. It's the quickest way; beats the crap out of twiddling with barrel adjusters and limit screws until you throw a wrench through the window. Use Park's instructions.
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Old 05-21-09, 01:14 PM   #6
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Middle chainring to small cog is not cross-chaining, you dopes.
Before you start calling people names, try reading the opening post, son. The OP uses very ambiguous language like "When I'm in the small or middle chainring" or "the smallest two or three cogs"... so it's diffucult to be exact with a diagnosis. But the overall description sounds like a classic case of a rider who isn't familiar with the sound of an untrimmed derailleur. Back in the friction shifter days, it's the kind of sound that prompted us to yell at newbies to "TRIM IT UP!"

And crosschaining is not a quantifiable measure... crosschaining is a matter of degrees. Anytime you're riding with a gear combination that results in a less than perfect chainline... you're crosschained. It only matters when it gets extreme enough to make noise or wear on the chain. So the gear combinations that the OP described can result in ticking or rubbing due to crosschaining. Dope.
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Old 05-21-09, 02:05 PM   #7
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The name calling is unneccessary, I'm just trying to diagnose a problem. Unhelpful responses can be ignored.

I am familiar with bike mechanics, and gave a very specific description. In either the small or middle rings and the smallest, second to smallest, and 3rd smallest the chain is rubbing on the outer plate. This is not due to cross chaining or trim, and this is not normal.

It doesnt look like it, but could it be a bent derailleur cage? The only other thing I see off is the chain is maybe a link too long. To my knowledge this wouldn't cause that problem though.
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Old 05-21-09, 02:11 PM   #8
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The only other thing I see off is the chain is maybe a link too long. To my knowledge this wouldn't cause that problem though.
You are correct... chain length wouldn't cause the symptoms that you describe.

If it's not bent or damaged, I'd try completely adjusting the derailleur again... high/low limits... tension... alignment.

After that... I dunno.
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Old 05-21-09, 02:48 PM   #9
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A bit more tinkering and turns out it's a chainline/shift pin issue, not a derailleur issue. The chain is catching on the shift pins when the derailleur's tension is properly set and the chain is not touching either cage plate. The chainrings say "cyclone" on them, and I can't tell what kind of crank it is though I would have to guess suntour from the cyclone name. The pins don't seem to be any larger than most cranks, and the chain rings are straight. What could cause this? I'm stumped now.
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Old 05-21-09, 03:27 PM   #10
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have you change the chain lately ?, let say you put on a 7spds chain and your bike need a 9 spds. the 7 spds will be a little to wider for your chainrings and yes you will get the rubbing/catching you describe. have you taken the crankrings apart ? maybe you put one or two on backward. have you check your chainline ? if it off in any way this can happen.you do not said anything about any service to the bike.like removing for cleaning or up grading. these are some ideas to check on.
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Old 05-21-09, 03:30 PM   #11
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Originally Posted by tellyho View Post
Middle chainring to small cog is not cross-chaining, you dopes.
Just a bit of friendly advice, telly: A certain member we're well acquainted with has been banned for 7 days for treating members like pond-scum for asking questions and offering advice - which is what we are all here for. With the pro-mechanics here to teach people - for free. Let's not follow this one, particular member down the rabbit-hole of insults and innuendo. It was a failed methodology that serves no purpose to pursue.

And that goes for rest of you moron's too! Der..........
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Old 05-21-09, 03:37 PM   #12
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Bikeman, good ideas! I actually just acquired this bike, so I don't know it's service history. I'll be sure to look at the chain to make sure it's a 9 speed chain. What's the best way to check a chainline on a geared bike?
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Old 05-21-09, 03:58 PM   #13
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check out sheldonbrown.com he have great info. about chainline and all.

Last edited by bikeman715; 05-21-09 at 04:12 PM.
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Old 05-21-09, 04:29 PM   #14
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check out sheldonbrown.com he have great info. about chainline and all.
Specifically.....

http://www.sheldonbrown.com/chainline.html

RIP, Sheldon. The legend ... lives on.
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Old 05-21-09, 05:13 PM   #15
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The derailleur is set up correctly. Outer plate is parallel with chain, tension is correct, limit screws are correct, outer cage is 2mm above chainring.
There's your problem right there! Bike-shops tend to teach their employees to adjust the FD so that the outer-cage is parallel with the chain. This gives consistent results, but consistently mediocre results. You actually want the cage to be parallel with the chain in the tallest gear. For most bikes, this rotates the rear of the FD outwards a little.

So on your bike, put it in the middle chainring and 3rd smallest cog and look at the chain. It's rubbing the FD right? Now imagine what would happen if you rotated the rear of the FD outwards? More clearance on the outside and no more rubbing!!!

Here's a good guide to FD adjustments: http://www.parktool.com/repair/readhowto.asp?id=75
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Old 05-21-09, 07:35 PM   #16
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The chain doesnt have a model number on it, just says KCM Narrow. It seems like ive seen some 7/8 speed chains that say narrow as well. I'll have to wait til tomorrow when I have a better ruler to try and measure it.

The chainline looks fine to me. It is the stock crank, though I can only assume on the BB.

All the chainrings are installed correctly.
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Old 05-22-09, 08:28 AM   #17
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try a shimano chain and the advise from DannoXYZ. he also right.
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Old 05-22-09, 11:24 AM   #18
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BTW, don't pedal backwards. It's a waste of energy and doesn't do anything to push the bike forwards. Unless you've got gears selected to have a perfect chainline (small-chainring+big cogs, middle-chainring+middle cogs, big-chainring small-cogs), pedaling backwards will ALWAYS cause the chain to want to climb or fall down the cluster on the top-run of the chain. No amount of derailleur adjustments will fix that. Unless you want to mount a 2nd rear-deraileur on top of the cogs as well.

As for chainline, you have to measure it. What is the distance from the middle-chainring to the centre of the seat-tube?
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Old 05-22-09, 11:36 AM   #19
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KMC Narrow is what I see on the 6-7-8 speed chains I use frequently. I have no idea if it's on their 9 or 10 speed models, but I'd be inclined to guess not.
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Old 05-22-09, 03:38 PM   #20
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I'll be putting on a shimano 9 speed chain tonight or tomorrow morning, I'll let you guys know if it works out!
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Old 05-23-09, 10:24 AM   #21
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I just installed a shimano 9 speed chain and made the suggested derailleur adjustment. It may have gotten a litttle better, but not much. The chainline measures 43-44 mm, inside surface of the middle chainring teeth to the middle of the seat tube.
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Old 05-23-09, 11:48 AM   #22
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try raising the dérailleur, no more than 4 MM and the chain doesn't bump into the tail of the dérailleur. the only other thing would be change the chain line by using a shorter bb unit.does the chain drop off the rear dérailleur's lower pulley ? if it does yes we have a chainline problem. does it do this pedaling backward and /or forward ?if it backward don't worry about.if it does forward it need work on the chainline.

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Old 05-23-09, 12:22 PM   #23
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I just talked to a friend and he suggested putting a spacer behind the drive side lockring on the BB. I tried it and it helped a bit, but didn't completely fix it. I might try finding a bigger spacer.

Bikeman, wouldnt using a shorter bb move the chainrings closer to the chain, thus making the problem worse?
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Old 05-23-09, 12:30 PM   #24
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The obvious adjustment is to increase cable-tension a couple clicks. And also use the trim positions.
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Old 05-23-09, 12:44 PM   #25
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yes,you'll need to move outward.it hard to tell you what to do without seeing the bike. sound like you are on the right track. if the spacer work then you might want to go with a longer bb axle which will also move out the crank & chainrings.
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