Keeping hub gears adjusted correctly is the single most important piece of maintenance you can do to them. You’ll most likely feel it if the adjustment starts to drift out and your bike may even take it upon itself to start shifting randomly when you least expect it. Be alert for any changes in the quality of your shifting and re-adjust sooner rather than later. Badly adjusted hubs will wear very quickly, requiring the replacement of expensive internals.
If these simple adjustments fail, it almost always indicates that some of the internal workings of the hub are already badly worn and will need to be replaced. This is the kind of fiddly job it’s worth having your bike shop do – mainly because the range of different hubs has grown to such an extent that ordering exactly the right spare parts can be a bit trial and error.
These instructions are for the 2006 Shimano eight-speed hub, but the general principles apply across all their hubs. All Shimano hubs have one common method of adjustment. The cable starts at the shifter on the handlebar and ends at a cassette joint on the righthand side of the hub. Shifting gear pulls the cassette joint around the hub in distinct steps, corresponding to the number of gears. One of the gears is always marked differently on the shifter. The number may be written in a different colour or have a circle around it. Set the shifter in this gear to adjust the cable tension.
The cable is the correct tension in this gear when the two halves of the cassette joint – the odd-shaped collection of plates that sits in the middle of the back wheel, between the sprockets and the frame – line up. They’re made with coloured tabs, so that you can get the alignment right.
These tabs can sometimes take a little bit of finding as they’re quite small and can be covered in road dirt. They may simply be short fingers of metal marked by a red stripe or they may be concealed beneath a tiny plastic window on the cassette joint. Once you’ve found the tabs, lining them up is simple. There will usually be a barrel-adjuster on the shifter – turn this and experiment to find out which way brings the tabs further apart and which way brings them closer. The alignment needs to be precise, with the two coloured tabs in as straight a line as possible, so you’ll find yourself making quarter- and even eighth-of-a-turn adjustments to find the right place. There are two possible locations for the barrel-adjuster. It may be on the shifter, where the cable emerges, or on the other end of the cable near the rear wheel. You may even have one at either end. It doesn’t make any difference which one you use, but if you’ve got a choice, use the one near the rear wheel, since it’s easier to see the adjustment tabs from there.
Step 1: Here you can see the number 4 on the shifter is written in red. This indicates that the hub should be adjusted with the shifter set to this position. This is the most common way to pick out the right gear to do the adjustment in, but another possibility is that the chosen gear may have a circle around it. Twistshifters work in exactly the same way – just set the shifter so that it’s lined up with the differentiated number.
Step 2: This view is looking down from above into the gap between the rear hub and the frame. In this case the tabs are underneath a clear plastic window – you’ll have to wipe the window clean of road dirt before you can see the tabs clearly. Older hubs have two small exposed fingers of metal with a red stripe painted on each. You can see here that the two stripes are not in line – the right one is slightly lower.
Step 3: If you look at where the cable emerges from the shifter, you’ll see the barrel-adjuster, which alters the tension in the cable. Turn the barrel-adjuster gently, while looking down into the gap and watching the tabs. You’ll see them move relative to each other. It’s not worth trying to remember which one has what effect – just turn so that they get closer, rather than further apart. When they’re exactly lined up, stop.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
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