| Replacing the Front Derailleur |
Replacing the front derailleur is one of those jobs that seems impossibly
complicated. But once you've done it, it seems ridiculously easy. The hardest
part is buying the correct derailleur for your bike.
How do you know you need a new front derailleur? (1) The cage won't hold its
shape. (2) The cage can be moved and forth more than a whisker when you wiggle
it with your fingers. (3) The mechanism sticks or catches despite cleaning and
lube.
How do you order a new front derailleur? You need the correct
"clamp size" (the clamp is the ring that anchors the derailleur to the
bottom of your seat tube). Clamps come in 1-1/8", 1-1/4", and
1-3/8". Most bikes will use the 1-1/4" size. If you're holding a ruler
against the bottom of the seat tube to see what size you need, you'll probably
underestimate the size. For example, if the outline of the tube falls exactly on
1-1/8 on your ruler, you probably need the 1-1/4 size. Front derailleurs can be
activated from top or bottom. You need to get a "bottom pull" (if the
cable comes into the derailleur from underneath the bike) or a "top
pull" derailleur if the cable comes down to the derailleur from above.
| First, you need to get the chain out of the way. (Unless you
have a rivet tool and the correct rivet to reassemble the derailleur
cage.)
If you have a "Quick Link" connector in the chain, that's
easy. Otherwise, use your chain-breaking tool to push out a pin. See
our chain repair section. |
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Remove the old derailleur.
Loosen the cable-clamp bolt with a hex wrench until the cable comes
free of the derailleur. |
| Unscrew the hex bolt that tightens the clamp onto the seat
post.
Remove the clamp from the seat post.
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Now put the new derailleur into position, right where the
old one was. Tighten the bolt on the clamp lightly -- only enough to keep
it from slopping around.
Check to make sure the cage of the derailleur will clear the large
chain-ring when the the hinge extends.
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| Take up the slack on the shifter cable and tighten down the
bolt on the retaining clamp.
Set the limit screws so the inner wall of the derailleur cage is 2 mm
(just less than 1/8 inch) away from the chain while in the small chainring
and the biggest biggest cassette cog, and the outer wall is 2 mm from the
chain while in big ring - smallest cog.
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Check the position of the derailleur cage. Shift the
derailleur over to the largest chainwheel. The derailleur cage (the long
thin "box" that moves with the chain) should be exactly parallel
to the chainwheel.
If necessary, loosen the clamp and turn the derailleur so it's parallel
to the chainwheel. |
| Check the height of the derailleur cage. It should barely
clear the teeth of the large chainwheel when sitting directly over the large
chainring. There should be about 1 to 2 mm or clearance. Adjust the height by loosening the clamp and pushing
the entire derailleur up or down, then tightening again. |
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