Rear Derailleur Adjustment
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Small Pozi screwdriver |
Notice the two small screws on the body of the rear derailleur. (some Suntour models have three screws ignore the top one for now.) The high gear limit screw stops the derailleur from shifting past high gear (smallest sprocket) and the low gear screw prevents it from going past low gear (largest sprocket). If a limit screw is too loose the chain will fall off. If too tight the system will not engage the gear.
Locations of the adjustment screws will vary on different brands, but they all function the same way.
1. Tighten the high gear screw, the one that hits a cam when you shift to the smallest sprocket, until you can no longer shift into high gear. Put the shifter in high gear position and while turning the pedals, unscrew the high gear screw until the system engages high gear again. Shift between high gear and the second smallest several times, backing the screw out a little more, just until the derailleur shifts smoothly.
2. Tighten the low gear screw until you no longer get first gear. Repeat the process for this low gear limit - back the screw out just until the bike shifts smoothly from the second largest to the largest sprocket.
3. If you cannot engage high or low gear, or if the above technique does not work for high or low gear, the cable may be improperly adjusted.
Shift into high gear and push the shifter all the way to the end of its travel. Loosen the cable inner wire anchor bolt. That's the bolt with a hole through which the derailleur control wire is clamped. Pull the slack out of the wire and retighten the anchor bolt.
If your bike has index shifting you'll find an adjusting barrel either at the derailleur or the shifter. The adjusting barrel is a hollow screw at which the cable outer housing stops but which the inner wire continues through. Fine adjust the cable tension by turning the adjusting barrel until the clicks on the shifter correspond with proper shifting at the derailleur.
If your bicycle does not engage high gear, or is slow to engage high gear, even though properly adjusted the cable is probably the culprit. Replace the sticky or rusted cable and the problem will usually go away.
If you have done everything right but the bicycle does not shift reliably the most common reason is that the chain and freewheel are too worn to work properly. If you replace one you must replace both. A new chain on an old freewheel or vice versa usually skips and the new part wears out very quickly.
Another possibility is a bent derailleur. The guide pulleys, those little wheels that take up the chain slack, must pivot on the same plane as the freewheel sprockets. Derailleurs become bent when the bike falls over on the right-hand side. Whenever you set a bicycle down, or put it in a car, set it on its left side to protect the derailleur. You can sometimes straighten out a bent derailleur by simply bending it back and readjusting the limit screws.
Front Derailleur Adjustment
| Time taken: 10min | Difficulty Rating:  |
| Tools Required | Small Pozi screwdriver |
The front derailleur is adjusted like the rear one - the principles are the same. Look closely to find which limit screw does what since their positions vary on different models of front derailleurs.
1. Make sure the front derailleur cage is parallel to and above the largest front sprocket by only about three millimetres (1/8 inch).
2. With the rear derailleur in high (smallest sprocket) tighten the front derailleur high gear screw until you cannot shift into high gear (large front sprocket). Back out the screw while turning the pedals and operating the shifter until you just get a clean shift every time.
3. Repeat this procedure for shifting down to the smallest front sprocket but with the rear derailleur engaged in low gear.
4. Check all combinations of front and rear gear selection. You may have to compromise the adjustments a little to get a clean shift in all cases.
5. Because the chainwheels (front sprockets) are probably not perfectly flat try all combinations of shifting when the pedals are at varying angles of rotation.
Sometimes front derailleurs will require a little bending to get proper function. If the chain sometimes falls off even though the adjustment seems correct, try bending the front edge of the derailleur cage in a little bit.
If the derailleur is reluctant to engage high or low gear the cable may need adjustment. Shift toward the largest sprocket, pushing the shifter all the way in its travel, loosen the cable inner wire anchor bolt, pull the slack out of the cable and retighten.
If that doesn't work, the cable may be sticky or rusted, and should be cleaned or replaced.
If you have done everything right, but the chain still falls off occasionally or the derailleur is slow to shift, consider the following points:
The chainwheels may be bent. If so you'll see them waver as you turn the pedals. You can simply bend them back into place. Do this carefully with a rubber hammer.
One or more teeth of the chainwheels may be bent. You may be able to straighten a bent tooth by grabbing it with an adjustable wrench.
The chain or the chainwheels may be worn out.
The chain or the chainwheels may be of low quality. This is common, and the usual cures are to ignore the problem, or spend money. Keep in mind that to get the performance we do get with bicycles, the engineering is a compromise between reasonable weight, features and cost. If you want perfection you've got to pay the price. The price isn't always money. Even if you spent a million dollars for the best bicycle money could buy, you'd still find some aspects of your machine which would be less than satisfactory. Hey, it's either settle or walk!
Skipping problems are not related to the derailleurs. If your bike has a skip when pedalling hard, check the skip frequency. If it is once for every revolution of the chain, there is probably a stiff link. Try lubricating and flexing the chain laterally. If the skip is once per each revolution of the front or rear sprockets then look for damage or build up of dirt on the offending sprocket. If the skip frequency is random the chain and freewheel are probably worn out and require to be replaced for best performance.