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Front Derailleur Question - Which one do I need?

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Front Derailleur Question - Which one do I need?

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Old 04-02-10, 11:33 AM
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JC 911
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Front Derailleur Question - Which one do I need?

I do alot of road biking but also have a mountain bike (2003 Klein Attitude) that I have neglected the past few years. Anyways, I was cleaning up the mountain bike this past weekend and have decided to put some love back into it. I need to change out a couple of components due to some rust showing (cassette and front derailleur). The rest of the bike is in great shape and I surmise that some water was left sitting on the cassette and fd to cause some rust to occur.

In any case, the current FD is a Shimano Deore, clamp on. I am looking to get a Deore XT to replace the old one but noticed that there are different swings (top, bottom).

Probably a stupid question but how do I know which one do I need? Is it as easy as just shifting on the bike to see which way it swings?
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Old 04-02-10, 11:47 AM
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If the cable go to the der. from the top then it's a top pull, if it goes under your bottom bracket to the der. then it's a bottom pull. Most often good der. can do both.
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Old 04-02-10, 01:29 PM
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The OP asked about swing, not pull. There are at least 4 things to look out for:

-Pull: See above.

-Swing: Bottom swing = derailleur body swings BELOW the clamp (like your road bike's FD probably is); Top swing = derailleur body swings ABOVE the clamp. This is not as important as the pull direction; many frames can accommodate either design. To be safe, just get the same design as your current one.

Edit, pics speak better than words:
Bottom swing: http://www.bikemagic.com/news/images...mech_03_hi.jpg
Top swing: http://www.evanscycles.com/product_i...e-type-fit.jpg

-Clamp diameter: The three main sizes are 28.6mm (1-1/8"), 31.8/32mm (1-1/4"), and 34.9/35mm (1-3/8"). Most newer Shimano MTB FDs are 34.9mm and include shims for the smaller sizes.

-Speeds: Front derailleurs work best when their speed matches the speed of the chain. E.g. 9-speed chains are narrower than 8-speed, so the width of the FD's cage is different.

However, before you go and change out the FD and cassette, how bad really is the rust? Often times the light rust on a cassette will come off pretty well with good ol' Tri-flow. Can the FD be cleaned off?

Last edited by JiveTurkey; 04-02-10 at 01:33 PM.
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Old 04-02-10, 03:56 PM
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Thanks for the info. Looks like I have a bottom swing with a 34.9 clamp diameter.

I tried cleaning off the cassette but the light rust spots are still there. As for the FD, I may just buy a new one as they aren't that expensive on ebay.
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Old 04-02-10, 04:55 PM
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Before replacing the cassette, try riding it. Good chance the rust won't affect anything. But if you still can't stand the look of it, that's your prerogative.
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