parts must be perfectly adjusted. One bolt just
half a turn out of line can disable the whole
system. So while modern derailleurs are easy to
use, a sensitive awareness of their mechanical
needs is necessary to keep them well-tuned.
Most minor adjustments are easily made and
most derailleurs follow the same_principles as
the ones illustrated below.
.1911(01 174 - A1(01 :-)11 ■ 1 I
TRANSMISSION MAINTENANCE I
GEAR RATIOS
Triple chainrings and an extra long
cage arm on the rear derailleur are common features of mountain and
touring bicycles. The arlditional chainring, long cage, and widely spaced cogs provide a much greater range of gear ratios than on a racing bike. Wide ratio gears require a longer chain and do not shift as quickly and crisply as close ratio gears on a racing bike.
GROUP SETS
Most transmissions are complete systems
of components, from shift levers through
to freewheel and hub, expressly designed to work together. Manufacturers usually
advise that substituting one component (such as a chain or freewheel) from a different brand may result in a poorer performance. Equally, a substitution
may be an improvement. Ask your
bike shop for advice.
tb-
Mounting holt.
ltri*
=Cable wire cap (Cable Cable wire
• Adjustable bolts Chain guide Cable guides *10 mor Crank holt dust cap holt .-160-F
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106
Cable anchor bolt4(0
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Chaining 175CYCLE MAINTENANCE
THE FRONT DERAILLEUR To position a front derailleur correctly use the shift lever to place the outer plate of the cage above the large chainring. Use the front derailleur mounting bolt to position the outer plate parallel to the large chainring, and 1-3 mm above it. A tighter clearance is required for the closely-spaced double chainrings, and a wider clearance for the broadly-spaced triple chainrings. Note: If your bike is fitted with Biopace rings, make your adjustments with the crank pointed downward in line with the seat tube, so that the high portion of the chainring is next to the cage plates.
FRONT DERAILLEUR ADJUSTMENT
Turn cranks by hand and run chain to the small chainring and
large rear cog. With triple chainrings, use the low adjusting bolt to set a clearance of 1-1 .5 mm between the inner cage plate and chain. With double chainrings, position the inner cage plate as close as possible to chain without touching it. Test cable for slack and if neccesary, adjust cable anchor bolt. Run chain to large
chainring and small rear cog. Use the top adjusting bolt to set the
outer cage plate as close as possible to the chain without touching
it. For a Shimano STI system, run the chain to the middle chainring and large rear cog, and use the cable adjusting bolt on the shift lever housing to position the inner cage plate as close as possible to the chain without touching it.
1
Mount the bike on a workstand orother device to raise the rear wheel off the ground. Turn the cable adjusting screw on the shift lever all the way in and
then reverse it two turns. Place the shift
lever in friction mode, turn the cranks by hand and run the chain to the small front
chainring and large rear cog. Turn the
low adjusting bolt in or out, so that the guide pulley is in line with the large cog.
2
Run the chain to the large front 2 chainring and small rear cog. Turn the top adjusting bolt in or out so that the guide pulley is in line with the small cog. Place the shift lever in SIS mode, turn cranks, and shift the chain from top cog to second cog. If it won't go, turn the cable adjusting bolt anti-clockwise to increase cable tension. If it goes too far,
turn the cable adjusting bolt clockwise.
3
rotate the cranks and increase cableWith the chain on the second cog, tension by turning cable adjusting bolt anti-clockwise. Stop just before the chain makes a noise by rubbing against the third cog. Check shifting operation on all cogs. If shifts to large cogs are slow, increase cable tension by half a turn. If shifts to small cogs are slow, decrease the cable tension by half a turn.TRANSMISSION MAINTENANCE I
TENSION ADJUSTING BOLT
Run the chain to the small chainring and the large cog. Turn
the cranks backward and adjust the tension bolt so that the guide pulley is as close to the large cog as possible, but not touching it. Turn the cranks, run the chain to the large
chainring and small cog and check that the guide pulley does not
touch the cog. Adjust if necessary.
REAR DERAILLEUR REMOVAL
If the chain is on the bike, you can mount or remove a rear derailleur by undoing the tension pulley bolt with an alien key (above) and removing the tension pulley. It may be necessary to loosen the guide pulley so that the cage sides can be moved far enough apart for the chain to clear the chain guard tab.
REAR DERAILLEUR MOUNTING In order for most modem rear derailleurs to work well, the rear wheel drop outs must be aligned with each other, and the derailleur hanger must be parallel with the centre line of the hike. Frame alignment requires specific equipment and a high degree of skill, and should be done by a bike shop. Field test: stand behind the bike and visually check that a line through the guide and tension pulleys is parallel with (in same plane as) the rear wheel.
Rear Derailleur Disassembly
Derailleurs are fun to play with. They need only a few tools for disassembly, and are small enough so that you can sit down comfortably in a chair while you strip one down, learn how it works, clean and lubricate it, and then put it back together in the
right order. Dismount a rear derailleur via the mounting bolt, first disconnecting the cable anchor bolt, and if the chain is on the bike, the tension and guide pulleys. From this point onward the technique for disassembly varies from model to model. The common feature is the cage stop screw which
prevents the cage from unwinding. Hold the cage and body firmly, undo the cage stop screw and unwind the cage, carefully noting how many turns it rotates. Similarly, when you separate the cage and arm, by undoing whatever obviously holds them together, make a careful note of the position of the spring. Most derailleurs are designed so that the spring tension, for example, can be easily adjusted by placing the end of the spring in one or another of a series of holes. If your transmission has wide-range gears, the spring tension should be taut. If the gearing is close-range, you may be able to use a softer spring setting for faster shifting.
Chain Length
Short-arm derailleur and double chainrings: you need a length of chain to pass over a large chainring and large cog, without going through the derailleur arm, plus two links extra. Long-arm derailleur and triple chainrings: with the chain through the derailleur arm and over the large chainring and small cog, the derailleur arm should point straight at the ground.
Lubrication
Periodically lubricate the pivot pins on the derailleur body, and clean and re-grease the guide and tension pulleys. Remove the pulleys by undoing the pulley bolts, clean in a biodegradable solvent, and re-grease with a light, fast grease (see pp.184-85).
Teeth
Pawl
RATCHET ACTION
One end of each pawl is pinned to
the inside part, the other end is held by spring tension against a series of indentations or teeth,
positioned inside the outer body. When the chain starts to drive the outer body clockwise, the pawls lock in to the teeth and the inner part of the freewheel then moves, driving the wheel.
Pedal drives chain causing outer wheel to rotate
COASTING
When you cease pedalling
so that the wheel and inner freewheel are moving, but the chain is not, the pawls ride over the indentations or teeth in the outer body. This is the fast clicking sound
you hear when coasting.
CASSETTE ANATOMY
Inner wheel continues to rotate after you cease to pedal
21-tooth (T) cog
Lockring
REPLACEMENT TECHNIQUES
Place the freewheel remover in the vice with the wheel flat down (it's side-on in the photo so you can see it), and turn the wheel anti-clockwise. Stop turning it as soon as the freewheel breaks free, and loosen the quick-release skewer or axle
nut, to prevent damage to the threads on
the hub. Turn the freewheel remover a little more and loosen the axle nut slightly, and spin the freewheel off the hub. Grease the threads on the hub before installing a freewheel. Work carefully, as misaligning and crossing the freewheel and hub threads will damage the hub.
CYCLE MAINTENANCE