BICYCLE REPAIR
Front Derailleur Adjustment
Round up the following:
Gripping each crankarm with one hand, push and pull laterally to check
for play in the bottom bracket (photo). If necessary, use the appropriate
bottom bracket (BB) tools to remove play. Depending on what type of BB you
have, you may need to remove the crankarm first. Any play in the BB bearings
makes it impossible to properly adjust the front derailleur. While you’re
working on the crankset, check each crankbolt with the 5-mm allen wrench
to make sure they’re tight.
Lift the chain off the smallest chainring and place it on the bottom bracket
of the frame. Turn the crank by hand while looking at the chainrings from
above. Using one side of the front derailleur cage as a reference, observe
the trueness of each ring. If they wobble, true them by prying gently with
the adjustable wrench (set the jaws just wide enough to slip over the ring).
Another way to do this is to tap on the wobble with a plastic mallet. This
takes a little practice, but it works nicely when you get the hang of it.Place the chain back on the ring. Next remove the cable end cap, loosen the anchor bolt with a wrench, and remove the cable from the housing (if applicable). Replace a rusted or frayed cable and cracked or corroded housing. Run the new cable through the lever, housing (or BB guide), and stops to the anchor bolt (photo). Don’t tighten it yet. Apply spray lube to the derailleur pivot points and wipe off the excess. Check the tightness of the cage bolt with a screwdriver.
When viewed from above, an imaginary line through the center of the derailleur
cage should be parallel to the chainrings. Next, look at the derailleur
and rings from the side. Pull the cage outward with your hand. It should
clear the large ring by 1/16 inch (photo). If necessary, loosen the
frame clamp with an allen wrench and adjust the derailleur position. 
Shift
to the largest freewheel cog and smallest chainring. Adjust the low-gear
(inboard) limit screw so there is 1/32-inch clearance between the inside
of the inner cage plate and the chain (photo). Clockwise turns
limit derailleur travel, and counterclockwise turns increase it.
Make sure the front shift lever is in its starting position (shift the
chain onto the smallest chainring by hand). Also, make sure that the cable
housing is seated inside the lever and the cable stop(s) because otherwise
when it pops into place, it’ll create slack ruining your cable adjustment.
When the cable and housing is seated correctly, pull lightly on the cable
with pliers to remove slack and tighten the anchor bolt with a wrench
(photo).
Shift
to the largest ring/smallest cog combination. Adjust the high-gear (outboard)
limit screw so there is at least 1/32-inch clearance between the inside
of the outer cage plate and the chain. Also, the cage shouldn’t travel
outward so far that it strikes the crankarm (photo).
Test your work by shifting repeatedly. Move the lever forcefully to stretch
the cable, then shift to the smallest ring and check cable slack (photo).
Remove slack if necessary as described in step 5. Go for a neighborhood
test ride. If overshifting occurs (the chain falls off), tighten the appropriate
limit screw half a turn at a time and test. If shifts are hesitant, looosen
the appropriate limit screw half a turn at a time.
This article
is based on one I wrote for the April 1991 issue of Bicycling Magazine.
The photos are by Mel Lindstrom. I set up the shots and appear in them.
The photos are by Mel Lindstrom. I set up the shots and appear in them.
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