Rear Derailleur Set-Up
This is the task which seems to faze so many cyclists, but unnecessarily, in my opionion. With the derailleur in its relaxed position, the cable can be connected. Typically, the shifter will be set to the highest (small) gear and so the cable is under virtually no tension. (Low-normal, or rapid-rise, mechs will be relaxed in the lowest (large) gear, so the shifter should reflect this).
Start by making sure the barrel adjusters are both (if there are two, as seen in the first two pictures below) turned fully clockwise, then, with the shifter in the highest gear, give the inner cable a little tug to make sure that it’s pulled fully through the outer, then hold it under the retaining bolt, making sure that it’s sat in the little groove on the derailleur and that the clamp part of the bolt is in the correct position (see third and forth pictures below). Tighten the bolt down so that the cable is secure. A work stand is ideal for jobs like gear indexing because it will allow you to lift the rear wheel and get the cranks spinning without having to hold onto the bike. However, you can set your indexing just as easily be flipping the bike upside down and making your adjustments from there. The screws for adjusting the derailleur limits are seen most clearly in the fourth picture. Positioning varies between models and manufacturers, but the limit screws are always found right next to each other and will be marked H for high gears (smallest) and L for low gears. It’s very important – to prevent the bolt-head being rounded out - that you use a suitable screwdriver for adjusting the limit screws; a large enough flathead or the correct size Philips-head. The weigh of the derailleur springs means that you’ll need quite a lot of torque to move the screws into their ideal position, especially the Low limit screw, and a poorly fitting tool will easily slip in the top of the screw, damaging the interface and making further adjustments impossible. Take good care…
Indexing the gears is basically about setting the cable to the correct tension so that the gear selected by the shifter corresponds to the gear that the chain runs on at the cassette. Shift or place the chain onto the second smallest sprocket and rotate the cranks to simulate riding. On Shimano derailleurs (not Shadow), turn the barrel adjust counter-clockwise until you hear the chain begin to catch on the third smallest sprocket, it’ll sound like ‘click…click…click’. When you hear this clicking, the adjuster can then be turned clockwise until the clicking has stopped again; it’s usually a quarter turn or so. (If you were to continue turning the adjuster anti-clockwise the frequency of the clicking will increase until eventually the chain shifted over onto the third sprocket).
SRAM or Shimano Shadow derailleurs are indexed by the same process, but their lack of barrel adjuster means that you must adjust the cable tension from the shifter. It’s good to get used to using the adjuster at the shifter on the normal Shimano derailleurs too, as it’ll allow you to make adjustments while riding, rather than having to stop riding and mess about with the derailleur.
With the initial indexing done, you can now set the high and low gear limits. First, shift onto the smallest sprocket and then use a small screwdriver to tighten the H screw at the back of the derailleur. If you do this slowly you should feel the point where the screw touches the derailleur body. Turn the screw a further half turn, shift back to the second smallest sprocket, then back to the smallest. The chain should drop cleanly onto the gear and rotate without any unusual noise. If it won’t drop onto the gear, loosen the H screw a quarter turn at a time until it will. The High limit can easily be checked visually from behind the derailleur, so take these instructions as merely an indication of the purpose of the limit screws and then take your time to get them dialled in.
The Low limit is set by carefully shifting onto the lowest (largest) gear, then using the same process you just used on the High limit. You should be finding that the chain shifts easily and cleanly onto the sprocket, but then that the lever is impeded, leaving you unable to shift the chain any further.
At home is the place for trial and error when setting your H and L limits. The High limit is not such an issue, but if the Low limit is set too far out you may end up with the chain dropping off the cassette and pulling the derailleur into the wheel spokes. For future reference, the results of this particular set-up failure often spawn threads on the forum which begin “I was just riding along…”. Keep your eye out for them.
For the lower limit, carefully shift all the way down to the largest sprocket, then screw the L screw in until it catches the derailleur body. Shift to the next smallest gear, then shift back down to check that the chain shifts cleanly. The idea is that you can shift easily (without having to put excessive pressure on the shifter lever) into bottom gear, but that the chain is prevented from being pushed up and over the sprocket and into the spokes of the wheel.
The body adjust (B) screw is used, as the name suggests, to enable you to change the position of the derailleur body relative to the sprockets. To make this adjustment, first shift the chain into the lowest (largest) sprocket, then procede by screwing the B screw fully in so that the head is flush with the derailleur. Then, with the back-end of the bike jacked up, turn the cranks slowly and start to loosen the B screw. You’ll notice as you do this that the top jockey wheel begins to get closer to the sprocket; continue to loosen the screw until you hear friction between the top jockey and the sprocket, then tighten the B screw again until everything turns quietly again.
Instead of using a crimp-on cover for the end of your cables, try a little heatshrink tubing. You’ll be able to pick this up in various thicknesses from you hardware or electrical store and it’ll make the job of removing cables much easier. No more cutting cable ends off, or trying to slide a crimp back over, just slide a new piece of heatshrink on to ensure that cable is kept dry and protected from fraying.
The Front Derailleur
This section is on its way when I get enough time with a bike that has a front mech (I run a 1×9 set-up).
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