December 17, 2013 1:28 am
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Adjusting derailleur cable tension, perhaps the most often required maintenance, is one of the most easily learned. Setting the tension usually requires no tools and setting the limits only requires a common screw driver.

Modern shifters common on multi speed bicycles require that the tension on the cables be set precisely so that they line up properly with each gear.

rear_derailleur

While out on the road, you may find that your rear derailleur cable has stretched slightly. This can usually be easily fixed by winding out the adjusting barrel (counter clockwise) on the rear of the derailleur a single “stop.” The adjusting barrel will stick on indentations as you unwind it. Begin by moving just one stop at a time until shifting improves. Pay attention to the orientation of the pulley wheels to the gears. They should be centered directly under a gear. If your shifting is further out of adjustment than an entire gear you may need to use a more thorough method of adjustment.

The best way to begin the more thorough method is to shift into the highest gear. This will be the one with the fewest teeth, furthest away from the rear wheel spokes. Make sure that you have clicked your shift levers to the last click, even if the derailleur does not move on the last click.

If you have paid close attention to your bicycle and any odd noises it makes, you are likely to only need to turn an adjusting barrel one or two “clicks.” The barrels snap into place every quarter turn to keep them from vibrating loose while riding.

Now shift down exactly one click while pedaling the bike. The chain should move on to the next cog but do not shift again if it does not. Begin winding out the adjusting barrel to the point where you are in the next gear and beginning to jump as the chain reaches the third highest gear. Wind the barrel back in until chain movement quiets down again. Shift through all the gears now, winding the barrel in or out more if necessary to make all shifts smooth and all gear combinations quiet.

The limit screws prevent the derailleur from shifting into the spokes or into the frame. While they are less likely to go out of adjustment, a bump to the derailleur during a crash can cause the hanger to bend. This can change the limits as well as cable tension adjustments and cause the derailleur to shift into the spokes. This can cause severe damage to both the bicycle and the rider.

After a suspected impact to the derailleur, the limits should be checked before continuing to ride. Assure that cable tension is correct then shift into the highest gear and adjust the upper limit screw (marked with an H) in or out so that the upper pulley wheel is directly under the highest gear.

rear_rear_der

Ideally the limit screw should be wound in as far as it will go until the pulley wheel begins to move away from the center of the gear. Shifting into the highest gear should stay smooth. If there is a delay, back out the adjustment about one quarter turn.

Shift into the lower gear now to adjust the lower limit. If cable tension has been set correctly, there should be no extra play. You can push the derailleur over with your hand to see if you can feel additional movement. Wind the adjusting screw (marked with an L) in until the derailleur only moves far enough to shift into the gear. Wind the screw in just to the point where shifting to the low gear is no long smooth and then back it out a quarter turn at a time until shifting is smooth again. ?

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This post was written by Tom

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