Rear Derailers
Rear Derailer
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Rear derailers sometimes wear out, but usually if they are bad it's because they're missing parts. Check for these parts, and if they're there, you can say it's OK.
In the lower left is the barrel adjuster where the cable housing stops. Some derailleurs don't have this part, but will instead have a hollow area where the housing fits. If there is a hole with threads on the inside, and nothing screwed into it, the derailleur is missing something.
The two similar screws limit the derailleur's travel, and the other circled screw holds the cable in place.
Also very important, although it isn't circled, is that the derailleur must have both of its pulley wheels.
There are also some rear derailleurs which have removable bolts to attach them to the frame. The bolt in this picture is at the upper left corner of the derailleur. If this part of the derailleur is hollow instead of having a bolt, the derailleur is missing a part.
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