Checking Your Front Derailleur
What is it and What does it Do?
The front derailleur is the mechanism that shifts your chain from chainring to
chainring. It moves from side to side as you click your front shift lever, carrying
the chain along with it.
What Needs to be Checked?
You should check your front derailleur to make sure it's functioning properly
and that it's free of grime and dirt.
How Often should I Check?
You should check your front derailleur quickly before each ride.
Check Procedure
To check your front derailleur, suspend your rear wheel off the ground. Rotate
your pedals with one hand and shift your front gear lever through its full range
of gear options with the other. If your front derailleur is properly tuned, your
chain will shift crisply from one chainring to the next without hesitating between
rings or overshooting them and jumping off the chainring set.
Common Front Derailleur Problems and Solutions
- Sluggish or Inaccurate Shifting
Front derailleurs typically malfunction because (A) the derailleur body is
not positioned properly, (B) the derailleur limit screws are not adjusted
correctly, (C) the mechanism is dirty or (D) the cable is damaged or improperly
tensioned.
Solution A - Repositioning the front derailleur
To check the position of your front derailleur, shift it so that the derailleur
arm is positioned over the outermost chainring. The derailleur "cage" (the
long, curved section of the derailleur that the chain passes through) should
be approximately 2mm above the teeth of the chainring (when viewed from the
side). The outer plate of the cage should be lined up parallel with the chainring
when viewed from above.
To reposition your front derailleur, loosen the derailleur mounting bolt
that holds it onto your frame. This bolt is typically located on the opposite
side of the seat tube from the derailleur body. Once you've loosened the
bolt, re-position the derailleur by sliding it up/down and/or rotating it
slightly from side to side. (Note: you may have to loosen the derailleur
cable in order to move the derailleur body. To do so, read the section below
titled "Setting the inner stop".) Be sure to retighten the mounting bolt
carefully before riding. If during this procedure you notice that your derailleur
cage is bent or damaged in any way, bring it into a full service REI bike
shop for service.
Solution B - Derailleur readjustment
More often than not, sloppy shifting is caused not by a poorly positioned
front derailleur, but by poorly adjusted limit screws. The derailleur case
swings back and forth from the derailleur body (in response to your shift
commands) to deliver your chain from chainring to chainring. It must move
from side to side within a very specific range to perform well.
Limit screws
The inner and outer boundaries of your derailleur arm's side to side movement
are controlled by limit screws. These small screws are typically located
next to one another on the main front derailleur body, either stacked horizontally
or positioned side by side.
Each screw controls one extreme of the derailleur's movement. The "outer
stop" screw determines the farthest distance that the derailleur will travel
away from the frame. The "inner stop" screw determines how close the derailleur
will travel in toward the frame. If you tune these 2 limit screws correctly,
your derailleur should perform without problems.
Which is which?
Bike manufacturers identify inner and outer limit screws in a variety of
ways. Most label them with an "L" for low gear (which refers to the smallest,
innermost chainring) or "H" for high gear (which refers to the largest, outermost
chainring).
Setting the inner stop
The first step in adjusting your front derailleur is to see how far it swings
in toward your frame. To do this, you must first shift the front derailleur
to the innermost chainring and let the tension out of the front derailleur
cable by loosening the small bolt that anchors the cable to the derailleur
body. Loosening this cable will insure that the arm is free to swing as far
in as it can go.
Next, shift your chain to its furthest inside position -- i.e., the smallest
chainring and the largest rear cog. Use your inner limit screw to position
the inner wall of the front derailleur cage so that there is 2mm of clearance
between it and your chain at the point where they come closest together.
Once you've set your inner stop, pull the derailleur cable taut and re-anchor
it securely. Do this while your chain is still on the smallest chainring.
Setting the outer stop
Once you've set your inner stop, shift your chain to its outermost position
-- the largest chainring and the smallest rear cog. Use your outer limit
screw to position the outside face of the front derailleur cage 2mm away
from the outer surface of your chain (at the point where they come closest).
Keep in mind as you make this adjustment that it's your derailleur cage that
keeps your chain from overshooting the outermost chainring and falling off
your bike. Since some shifting systems (particularly newer ones) do not automatically
shift the derailleur out as far as it can go when they shift it to the largest
chainring, pull outward on the front derailleur cable slightly as you set
and test your outer limit adjustments. The added cable tension will insure
that the derailleur is really in its outermost position and that the chain
cannot be thrown.
Barrel Adjustments
Most modern bicycles have fine-tuning devices called barrel adjusters built
into their derailleur systems. These simple, round adjustment knobs, typically
located along the derailleur cable path at the base of your shift lever or
the derailleur body itself, allow you to fine tune your derailleur adjustments
by increasing or decreasing the tension of your shift cable very slightly.
Not all derailleur systems have barrel adjusters. But most bikes with "indexed" derailleur
systems do. Barrel adjusters are typically used to tune the position of the
rear derailleur more often than the front.
- To fine tune your front derailleur using your barrel adjuster, start
with your chain on the largest chainring and largest rear cog. Shift
your chain down to the next smallest chainring and check to see how close
the inside surface of the chain is to the inside wall of the derailleur
cage. The two surfaces should be as close together as possible (approximately
.5mm) without touching. Turn the barrel adjuster counterclockwise (a
quarter turn at a time) to move the derailleur cage inward, away from
the chain surface. Turn it clockwise to move the cage outward.
NOTE: If shifting difficulties persist despite the adjustments described
above, you may have a more serious shifting problem. Persistent shifting
problems should be addressed by an experienced bicycle mechanic.
Front Derailleur Cleaning Procedure
Many front derailleur problems are caused by dirt, grime or insufficient
lubrication. Even small amounts of grit and grime can cause problems, so
keep your derailleurs as clean as possible at all times. Re-lubricate them
every month or so (depending upon riding conditions) to keep them functioning
properly.
Clean your front derailleur by brushing all exposed parts with a stiff brush
to remove grit or grime. Stubborn grit can be loosened by wiping the derailleur
with a clean rag soaked in solvent. Be sure to clean the derailleur mechanism
carefully, including the hard to reach areas of the main derailleur body
and the derailleur arm.
When re-lubricating, focus on the moving pivots of the derailleur mechanism.
Use a drip lubricant designed specifically for bikes, and be sure to shift
the derailleur back and forth while applying it so you can work the lube
into the tough to reach places. Wipe off excess lubricant carefully when
you're done.
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