in order to service and fine-tune the
rear derailleur we first need to
understand how it works
hello Calvin Jones here Park Tool
Company the rear derailleur is the
mechanism that sifts the chains at the
rear sprockets there are many different
models but they all share the same basic
design and functionality derailleur is
are secured to the bike with a mounting
bolt to the frames derailleur hanger the
upper pivot of the derailleur is
connected to the lower pivot by a
linkage system that forms a
parallelogram derailleur is used a cage
fitted with two pulleys the lower pulley
pulls back to give tension to the lower
section of chain it is called tension
pulley or T pulley for short the upper
pulley guides the change of the
sprockets and it is called the guide
pulley or G pulley a mechanical type
derailleurs a cable is secured at the
pinch bolt when the cable is pulled the
cage is moved inward a return spring and
the linkage will move the derailleur in
opposite direction when the cable is
released with electronic shifting
systems an electrical signal triggers a
motor to move the linkage there is no
cable involved in these systems a
derailleur cable passes through the
housing to a shift lever
buycks commonly use an index shifter
that moves the cable in small
predetermined increments with each click
pulling or releasing the cable moves the
guide pulley barrel adjusters can be
located at the derailleur body or the
shift lever they are used to correctly
adjust the shifting between cogs on
threading or turning the barrel adjuster
counterclockwise effectively shortens
the cable moving the G pulley to the
left or inward turning the barrel
adjuster clockwise effectively lengthens
the cable this moves the G pulley to the
right or outward derailers are fitted
with limit screws which are adjusted to
stop the derailleur from shifting too
far inward or too far outward we can
actually see what the limit screws are
doing in this model the end of the limb
screwed strikes the linkage and this
stops the pulley travel
you
the L screw determines the limit of the
innermost caged travel tightening the L
screw will restrict the limit to the
left side
the aide screw determines the limit of
the outermost cage travel tightening the
h limit screw will restrict the limit to
the right side it is common defines
another adjustment screw on the
derailleur body called a B screw this
controls the size of gap between the
guide pulley and the sprockets those are
the basics of the rear derailleur now
that you have an understanding of how it
works watch this video to learn how to
properly adjust your derailleur to see
all a derailleur videos in one place
check out the punc tool guide to
doraleous
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