Fine-Tuning Index Shifting
Check that the derailleur limit screws, 'H' and 'L' are adjusted correctly.
should not come off of the cassette when shifting. The 'H'
screw limits the rear derailleur travel towards your smallest cog while
the 'L' screw limits how far the rear derailleur can travel to the largest cog.
Once you have the travel of the derailleur correctly set using the'H' and 'L'
screws, the only problems that you should ever run into should be a function
of cable stretch or derailleur damage.
Pre-stretching Your Cables
After replacing any cable (brake or derailleur), the cable will stretch. This
will cause the shifting to become sloppy and slow and the brakes to feel loose.
Both brake and derailleur cables will require continual adjustment as cables stretch gradually during usage.
Pre-stretching the cable is a good way to avoid a readjustment of your controls
after an overhaul. With brakes, it's simple. After cable replacement, squeeze
the levers as hard as you can, bringing the levers as close to the handlebar as
possible. This brute force will stretch the cable more than normal braking ever
could. Afterwards, loosen the brake cable anchor bolt and remove the added
Removing derailleur cable stretch is a bit more complicated than brakes.
Shift the derailleurs to the position closest to the center, from left to right,
of the bike. Without turning the cranks or moving the wheels, shift the
shifters to release all of the cable. Grab hold of the bare cables where they
are exposed along the frame and pull as hard as you can, away from the
bike. This will pre-stretch the cables harder than any shifting could.
Remove slack at the anchor bolts or by using the barrel adjusters.
Knowing your limitations. There are two limit screws, which are labeled with a tiny H and L. In the rear, the high limit screw can be screwed in to prevent the chain from falling off into the frame. If it's screwed in too far, the chain won't move into the easier gears.
The low limit screw prevents the chain form falling off the large cog into the spokes. The high limit screw prevents the chain from falling off the smallest cog into the frame. The chain should be free to reach the largest and the smallest cogs without falling off in either direction.
There are two types of shifters found on road bikes and mountain bikes, FRICTION and INDEX. Both types of shifters require the rider to change gears by moving a lever of some type. Index shifting has distinctive clicks for each gear. Friction shifting requires the user to 'find' the correct gear by sound and feel.
Friction shifting is easier to maintain but less user friendly. To identify which type of shifter you have, just move the lever one way or another. Friction shifters are quite, and index shifters have clicks that can be heard.
Maintenance of friction shifters is very simple, but it is up to the rider to adjust the shift lever until the bike is solidly in a gear. The rider will hear a rattle until the chain is aligned on a specific cog.
Most bikes made in the last thirty years will have index shifting, where one click of the shifter equals one shift of the derailleur. It is easier to shift but can be tougher to maintain. Maintaining index shifting involves adjusting the tension of the shifter cable so that one click of the shifter moves exactly one gear.
To tighten or loosen cable tension you must turn the barrel adjusters. There is usually one located at both ends of the shifter cable.
There are single speed bikes, internally geared bikes and derailleur bikes. Children's bikes are most often single speeds with a coaster brake. These don't often require service, but when they do, it's time to visit the bike shop.
Internally geared hubs most often come in three and seven speed types. All the mechanism is inside the hub, protected from dirt and damage. The hub itself is a complex mechanism and if it breaks, only a bike shop will be able to make repairs.
Internally geared hubs require lubrication from time to time and often have a port on the top in which oil can be added. Make sure to find the correct type of oil for your hub!
Internal hubs are cable operated, allowing riders to select gears from a shifter on the handlebar. Cables stretch over time and the shifter may not reach all of its gears. Tightening the cable, most often with a barrel adjuster, will compensate for a stretched cable. Barrel adjusters will either be located on the shifter or where the cable connects to the hub. Internal hubs don't offer the same gearing range as derailleur-equipped bikes, but will give years of trouble free riding with little or no maintenance.
Cables and cable housings are important to the operation of shifters. If they're rusted or dirty, the bike won't shift well, and you should consider buying a new cable and re-threading it. Bike shops can sell you cables, housing and cable cutters (standard wire cutters will often crush bike cables, instead of giving a clean cut). There are different kinds of housing for shifter cables and brake cables.
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