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Figuring out the correct front derailleur

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furicle Offline
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Posts: 2
Joined: Sep 2012
Post: #1
Figuring out the correct front derailleur
Hi All

First post, be gentle please :-)

I've got a 'yard sale special' Raleigh mountain bike I'm trying to fix up.
I've pretty much got it road worthy, except for the front derailleur. It's 3x5 gearing, but I cannot get this derailleur to use the highest gear regardless of adjustment. I originally replaced the shifter thinking that was the issue, but it's not. I'm pretty sure it's been 'frakenbiked' and it's a 2 range derailleur put on it in error.

So,
  1. How do I figure out the right one for it? What do I look for?
  2. Does anyone have a favourite online Canadian supplier?

I'm trying to be thrifty - not restoring a classic...
Sep 11, 2012 10:54 AM
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DaveM Offline
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Posts: 1,296
Joined: Aug 2008
Post: #2
RE: Figuring out the correct front derailleur
On derailleurs for 2 chainrings, the inner and outer plate of the deraileur usually both have a smooth curve that matches the curve of the chainrings with the inner sitting slightly below the outer.

On derailleurs for 3 chainrings, the inner plate will sweep down a lot lower and will have step in in where it goes from curved to horizontal.

I'm assuming that you have already tried letting out the outer limit screw which will keep the der from going as far as it could to the outside.

For a new der, if you don't have indexed (click into place) shifting, you can use almost anything, as long as:
- it is made for triple (3) chainrings
- has the same "clamp diameter" (the diameter of the frame tube it clamps on to)
- matches which direction the cable comes out. ("bottom pull" or "top pull"). I'm guessing you have bottom pull where the cable goes down under the bottom bracket before going back up to the shifter.

Note that another source of the problem could be that the bottom bracket spindle (the axle that holds the cranks) is too long. This pushes the carnks out away from the bike past where the der can get the chain to. Look at the gap between the teeth of the chainrings and the frame tube that runs back to the center of the rear wheel. If that gap is more than a cm or two, this COULD be the problem and a new der won't help.

Pics will help.
Sep 11, 2012 02:52 PM
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nfmisso Offline
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San Jose, CA
Posts: 2,047
Joined: Jul 2010
Post: #3
RE: Figuring out the correct front derailleur
After you cover everything Dave mentions; I like the Shimano M413 a great deal. I have purchased many items from Crosslake Sales on ebay (and Amazon) over the past few years, always great to deal with.

Nigel
Sep 11, 2012 03:06 PM
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furicle Offline
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Posts: 2
Joined: Sep 2012
Post: #4
RE: Figuring out the correct front derailleur
Thanks - good things to look at. I'll let you all know what I find.

I did check the set screws - it's one of the reasons I'm pretty sure it's wrong as the inside stop was all the way in and the outside stop was all the way out just to make it possible for it to cover all three gears.

If I make sure they are both backed off as far as possible I can make it move far enough with my fingers, but there's no way I can it with the cable without a ridiculous amount of pull. Yet it'll shift between the lower two rings pretty easy.

(Sep 11, 2012 02:52 PM)DaveM Wrote:  Pics will help.
Sep 11, 2012 06:44 PM
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Bill Offline
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NY,USA
Posts: 2,765
Joined: Sep 2009
Post: #5
RE: Figuring out the correct front derailleur
Try lubing the pivot points (screws that hold it together) and work it back forth a few times to see if it is gummed up.

Good maintenance to your Bike, can make it like the wheels are, true and smooth!
Sep 11, 2012 10:06 PM
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Bob R Offline
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Posts: 1
Joined: Sep 2012
Post: #6
RE: Figuring out the correct front derailleur
(Sep 11, 2012 03:06 PM)nfmisso Wrote:  After you cover everything Dave mentions; I like the Shimano M413 a great deal. I have purchased many items from Crosslake Sales on ebay (and Amazon) over the past few years, always great to deal with.

I am interested in buying a Shimano M413. One question regarding installing the FD M413 -- can the cage be opened to insert the chain? I do not have tools to remove and insert a chain pin and would like to open the cage. I read that some cages have a screw in the tail that allows one to open the cage. Does M413 open up at the tail end or is it riveted? Also, looking at photos it appears that there is a space in the front (head) of the cage between the outer wall and what appears to be a flange in the inner wall -- is the space sufficient to let one push the chain through the gap?. Appreciate your valuable opinion. Many thanks!
Sep 13, 2012 04:23 PM
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nfmisso Offline
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San Jose, CA
Posts: 2,047
Joined: Jul 2010
Post: #7
RE: Figuring out the correct front derailleur
(Sep 13, 2012 04:23 PM)Bob R Wrote:  ......
I am interested in buying a Shimano M413. One question regarding installing the FD M413 -- can the cage be opened to insert the chain? I do not have tools to remove and insert a chain pin and would like to open the cage. I read that some cages have a screw in the tail that allows one to open the cage. Does M413 open up at the tail end or is it riveted? Also, looking at photos it appears that there is a space in the front (head) of the cage between the outer wall and what appears to be a flange in the inner wall -- is the space sufficient to let one push the chain through the gap?. Appreciate your valuable opinion. Many thanks!

Sorry Bob, I don't recall, I am in China for another week+. I installed it on a frame up build, so I did not join the chain until after I threaded it through.

Nigel
Sep 13, 2012 04:34 PM
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Bill Offline
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NY,USA
Posts: 2,765
Joined: Sep 2009
Post: #8
RE: Figuring out the correct front derailleur

Good maintenance to your Bike, can make it like the wheels are, true and smooth!
Sep 13, 2012 04:48 PM
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