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What front mech to get?

Old 09-13-13, 02:36 AM
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JT101
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What front mech to get?

I've got a 26" folding commuter bike, with 7 speed cassette (11-32T) on the rear.

Crankset is Shimano FC-M341: 28/38/48

I just cannot get my FD-511 Front mech to shift properly. Played with limiting screws but it jumps off top chainring if I hold lever too long. If I adjust limiting screws to stop this, it then has problems with the smaller chainring.

From this site: http://velospec.com/components/shimano/fdm511
Total Top-low Max. Capacity 22T
Top-middle Min. Capacity: 12T
Top Gear Teeth: 44/48T


So it seems ok. However, the radius of the largest chainring and the mech are completely different. Could this be the problem?

Recommended mechs for this crankset is FD-310, and FD-311. Not sure what the difference is between these two, or why they're particularly suited?

If mine is already suited for a 48T ring, seems no benefit to change it.


Any thoughts appreciated


Cheers
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Old 09-13-13, 05:19 AM
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dsbrantjr
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"it jumps off top chainring if I hold lever too long. If I adjust limiting screws to stop this, it then has problems with the smaller chainring."
The high limit screw which would keep the chain from overshifting past the large ring has no influence on the behavior regarding the smaller ring and vice versa.
Your derailleur looks way too high above the large ring and may not be correctly sized for your 48-38 large-middle ring; these may be related. The 12T minimum top-middle rating means that you need at LEAST that difference so that the cage does not strike the middle ring on its way down; this may be why the derailleur is mounted so high. The FD-310/311 are rated for a 10T large/middle ring difference so may be better suited for your setup.

"Playing" with screws without a systematic approach may not be productive. Try following this procedure from start to finish without skipping any steps: http://www.parktool.com/blog/repair-...ur-adjustments
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Old 09-13-13, 07:25 AM
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Shimano disagrees about the 48T large ring-
http://techdocs.shimano.com/media/te...9830612824.pdf

I'm using a FDER designed for 22-32-44 on my Globe that I have 22-32-36.
I have a gawdawful gap on the large ring and I had to really tweek things to get it to shift.
The FDER cage just BARELY clears the middle ring. Else I won't get all 3 gears.
My other bike has the same set up except a 38T large ring. It shifts fine, but I had to do the same tweeks.
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Old 09-13-13, 07:31 AM
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Is this a new build or did it just suddenly start having problems. Front derailers can be very touchy to get right the first time.
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Old 09-13-13, 09:15 AM
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For starters, you appear to have the front derailler set way too high. You want it to barely clear the large chainring. Yours appears to clear it by a significant amount. Also make sure it is aligned to the chainring properly (parallel to the outer ring). Once that is done, then follow the Park Tool instructions for setting the limit screws.
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Old 09-13-13, 09:17 AM
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Oh, and replace that derailler cable (and probably the housing too given what appears to be a well-used bike). With so much fraying, I wouldn't be surprised if it snapped tomorrow.
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Old 09-13-13, 10:05 AM
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Wouldn't be a bad idea to start wiping off the chain after lubing it, too.
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Old 09-13-13, 10:44 AM
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Originally Posted by joejack951 View Post
For starters, you appear to have the front derailler set way too high. You want it to barely clear the large chainring. Yours appears to clear it by a significant amount. Also make sure it is aligned to the chainring properly (parallel to the outer ring). Once that is done, then follow the Park Tool instructions for setting the limit screws.
The suggested distance from Shimano is 3 mm. This is, conveniently, the thickness of a nickel. I keep on my work stand for just that purpose. I would suggest resetting the height as have others, JT101.

As for your other problems, you have two of them. The outer limit screw should be set so that you can shift up into the outer ring, not have the chain rubbing on the derailer in the highest gear and it shouldn't let the chain jump off. That should be easy enough to do.

Your other problem of not being able to shift into the lowest gear is related to cable tension. You cable is too tight so it won't let the chain drop on to the lower gear. While off the bike, shift all the way down on the front. Get the chain to drop into the lowest gear and pull at the cable like you were plucking a guitar string. The cable should be taut but not tight. If it is tight, back the adjustment barrel on the shifter off a little bit. A half turn may be a lot. You may also need to adjust the inner limit screw a little to get the derailer over far enough to drop the chain.

So, the order of business is to lower the derailer using a nickel as a gauge, adjust the outer limit screw, replace the cable, adjust the inner limit screw and adjust the cable tension. Enjoy playing with the limit screw now because you shouldn't touch them ever again...unless someone screws around with them.
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Old 09-15-13, 12:34 PM
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Solved it! Found an old FD-MC17 front mech. No tech specs available online, but seeing as the FD-MC18 has Top-middle Min. Capacity: 10T, I assumed my FD-MC17 also had. And now it works. The radius matches the chainring closer. So I think the middle ring capacity was the problem.


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Old 10-06-14, 04:48 AM
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Hi everyone again. So now I'm having problems with this derailleur. I did all the things suggested above for my old mech with this FD-MC17 but the problem I have now is that mech can shift from small to middle to large, but when I try to shift down it drops straight to the small ring. Won't stop at the middle one. I've played several times with the limiting screws and tension on the cable but to no avail. I took it to a big chain bike shop, but they said it was just worn out.
It seems to me the mech is stretched to the outmost limits. It feels like it's very temperamental. As soon as I adjust the screws a fraction one way or the other it stops working at the top or the bottom.

My large chainring is very big for a MTB/commuter setup: 48T. The front mech radius still looks far too small

The
FD-310/311 are too difficult to get hold of here in the UK, and I don't want to try a FD-MC17 again

I'm wondering if there is a more up to date front mech that will meet the specs

So to reiterate, I have a BB of 113mm,
Crankset is Shimano FC-M341: 28/38/48, and 7 speed cassette (11-32T)

Need a top pull, top swing mech

Thanks
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