I have a 18 speed bike with shimano derailures and grip shifts. I know the back derailure is out of whack.. Meaning the cable is out of adjustment, and it is slightly bent.. Should I try to un-bend and adjust? Or just buy a new one?? And could some one explain the proper way to adjust gears?? I have never been taught the proper way to do it. Thanks again!
Adjusting the rear derailleur of a bicycle can be a mystery to say the least, and there are many variables that come into play. If the rear hanger tab (This is were the derailleur connects to the bicycle) is out of alignment and/or the derailleur is bent, you could drive yourself crazy trying to make a perfect adjustment. It just won't happen. There are specialized tools to check the alignment of and to realign the rear hanger tab. However, an experienced mechanic can use an adjustable wrench and a good eye to bring things back to an acceptable tolerance. As for a bent derailleur, if it is not damaged it could be bent back simple by grasping it firmly and pulling it back into alignment. I have no way of telling what type of derailleur you have and whether or not your derailleur is connected to your bicycle via a hanger tab or directly to the rear drop out, but either way proper alignment of the derailleur with the center line of the drive train is critical in order to properly adjust the rear gear shifter (Derailleur).
Normally, when the derailleur needs adjustment it is not actually the derailleur that is the culprit. The outer limit screws once adjusted properly should remain in their fixed positions indefinitely. It is a combination of the outer cable casing that has compressed and the inner cable stretching. All you need to do in most cases is to turn the cable adjustment barrel on the rear derailleur a half turn counter clockwise (as you are looking at it from the rear) and go for a test ride. If the shifting seems to be better or not as bad then you are on the right track. If it got worse, then turn back the other way. Trial and error will usually get you dialed in. Normally this would be done while the bicycle is secured in a stand as you turn the cranks by hand. Just remember that cable tension is usually the culprit, but not always. There is also a cable tension barrel at the gearshift mechanism on the handlebars. It will do the same exact thing except at a different location. Also keep in mind that all derailleurs are not created equal and the lower priced models, although shifted fine when new will soon come out of alignment and not stay in adjustment if ridden beyond casual riding.
As for the outer limit screws on the derailleur, the proper way to adjust them is to disconnect the cable and allow the derailleur to float back and forth without being restricted by the cable. You would use your hand to through the derailleur from one extreme to the other making adjustments with a screw driver.
This info was contributed by DoItYourself Community member Woodrow.