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Having trouble with the front derailleur - chain rub.

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Having trouble with the front derailleur - chain rub.

Old 11-07-12, 04:49 PM
  #1  
Giga
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Having trouble with the front derailleur - chain rub.

I just bought a brand new Diamondback Trace online. I was able to assemble and adjust everything (through a combination of googling and youtubing) just fine BUT the front derailleur is very fussy.

Right now the main problem I have with it is that the chain is rubbing the outer cage when the rear is on the outermost ring (smallest) and the front is on the middle ring. If I adjust the barrel adjuster I can get it to not rub, but then when I shift it to rear innermost and front middle, it will rub the inner cage. I've already adjusted the cable and the limit screws (and think they should be correct) but it's just the middle that's not working.

Any advice?

Also, I may or may not have stripped one of the limit screws, can they be easily replaced?

Thanks!

EDIT - It's a Shimano Acera with triple chainrings

EDIT 2 - Notice if I have outermost front ring and rear 2-6 (everything but inner and outermost rear) it rubs the innercage.

Last edited by Giga; 11-07-12 at 05:18 PM.
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Old 11-07-12, 05:13 PM
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Back in the day we used a friction shifter , the chain guide cage plates
were re centered over the chain with each shift, to quiet any rubbing.

(BTW this comes up all the time with Shimano 3 big kathunks Indexing ..
search function is your next tool )

Park tool tries a step by step how-to on their web site
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Old 11-07-12, 05:38 PM
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+1

You need to learn to live with that or adjust that to the milimiter, either way shimano stuff is like that all the time, specially the low end triple stuff. Hail to campy tho...
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Old 11-07-12, 05:54 PM
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Does the front shifter allow you to make small movements in the front derailleur, or does it only have three clicks? If the former, get used to "trimming" a little as you move from one side of the cassette to another. Fact of life.
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Old 11-07-12, 06:08 PM
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First make sure the derailleur is positioned correctly - height/rotation - per Park Tool guidelines (google park tool derailleur), as there is no guarantee at all that it's correct from the factory, or that it did not get rotated in shipment. In addition to that and trim adjustment make sure you do not have too much space between innner side of cage and chain when in the small front - larger rear (low gear) position. That would give you more rubbing in the other position.
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Old 11-07-12, 06:20 PM
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+1 on using the Park Tool procedure all the way from the beginning, as if it was a new build, which it really is. And cny-bikeman's suggestion regarding the low limit setting is right on; I always set it so that it just barely stops rubbing in the small/big combo. Any additional clearance here takes directly away from clearance on the other end of the derailleur travel.
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Old 11-07-12, 06:42 PM
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I've followed the Park Tool procedues multiple times (all in all with reset and readjust, probably a dozen times now).

The problematic gears right now (all minor rubbing) from what I can tell is

2-1, 2-7, 3-1, 3-2, 3-3

3-1 i can understand because it's cross-chaining, but the rest, especially 3-3 doesn't even seem close to the extremes.

I did some googling on the Shimano triple derailleurs and read that you should only expect about 4 perfect rear gears per front gear. Is that true? and if so, should I leave it as is right now?
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Old 11-11-12, 03:59 PM
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I've given up on since those gears will probably be my less commonly used ones. Will chain rub cause serious damage to the FD/chain in the long run?
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Old 11-11-12, 05:18 PM
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+1 on that, just avoid the extremes and you should be just fine.
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Old 11-12-12, 01:26 PM
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I just read the techdocs on that front shifter, and I guess it is index-only. So you'll only be able to use a couple of the cogs with each chainring -- that's a bummer.
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Old 11-12-12, 04:50 PM
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Having rub on only 5 out of 21 combinations is pretty typical, if not better than average without a trim option. There is so much overlap in a triple that you likely have a useable combo that is close in gear ratio to the problematic ones. Just Google "bike gear calculator and plug in your chainring and cog sizes. You'll see quite a few that are near duplicates.
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There's no such thing as a routine repair.

Don't tell me what "should" be - either it is, it isn't, or do something about it.

If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

Please respect others by taking the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!

Last edited by cny-bikeman; 11-13-12 at 03:44 PM.
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Old 11-13-12, 12:35 PM
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People think that if the bikes come with 21 combinations they can use them all, besides from the 21 you have many that are almost repeated 2 to 3 times.
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Old 11-13-12, 01:05 PM
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A couple of things you can try: 10 speed (narrower) chain.

Spread FD cage open a little wider.

Make sure FD cage is parallel to chainrings, not rotated.

All my bikes with 3x7 give me all 7 rear on the middle front chainring with no rub.

All 7 in the rear w front @ 1 or 3 is a little harder, but I have done it.

The shorter the wheelbase the harder it is to avoid chain rub.

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