How do you adjust the rear derailleur of a bike, so that the bike will change gears?

I have a used bike, and before I got it, it sat out in the rain, and now the rear deralleur will not shift. I can shift it manually, just by pushing the derailleur back and forth with my bare hand, but when I try to shift with the shifter on the handlebars, the shifter will not move. I already adjusted the extera slack off the cable (there was quite a lot of that), and i also coated the thing with silicone lubricant spray, but it still will not shift.How do you adjust the rear derailleur of a bike, so that the bike will change gears?
Here is a diagnostic. It is a little long, but if you go through it you should be able to find your problem.



1) Attempt to shift the bike to high gear... that is the smallest gear in the back. Remember, you must pedal FORWARD as you shift;

2) If it goes into gear, great. If not, pull on the cable at a bare area. There should be no tension AND no slack. If there is tension on it and pulling it makes it slack, pedal the bike forward and it should drop into high gear.

3) If it DOESN'T go into high gear there are one of 2 things wrong... either someone messed with the ';H'; adjuster screw on the derailleur or the derailleur is broken/frozen. Back the ';H'; screw out a little and see if it makes any difference. If it does, turn the screw out as you are pedalling until the pulleys on the unit line up with the smallest rear cog.

4) If it DOES go into gear then your cable or shifter is bad. My guess it is probably the cable. You will need to remove cable AND housing and replace it. Just slathering with lube usually won't do it.



My guess, based on your explanation, is that the cable or shifter requires REPLACEMENT, and it is most likely the cable.How do you adjust the rear derailleur of a bike, so that the bike will change gears?
That cable is corroded internally most likely, or the shifter's rusted up.



One other possibility is that the cable has become disconnected at the shifter end (I wonder where all the extra slack came from?)



If you disconnect it from the derailleur, does the cable move freely when you change gear?
Agree with above, replace cables AND housings to trust it.

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