Trouble with chain & rear derailleur pulleys

[generic_cyclist]

Hi,

While fixing a broken chain, the chain came completely off of my rear derailleur. I fed it back through (in a way I thought was right) and fixed the chain. When I tried riding the bike again, it pedaled smoothly at first but gradually became choppier and then became so slack that pedaling was ineffective.

In trying to figure out what went wrong, I noticed that the arrangement of the rear derailleur pulleys had changed. The first two attached photos show what they look like now. They basically do nothing to support the chain. If I hold the lower pulley back, as shown in the third attachment, the chain appears to feed through everything properly, but when I let go, the pulley springs back to the position in the other photos. The upper pulley can also be pushed forward (so that the part in the photo that says "GOLDEN-SUN" would be horizontal), which is how every photo of normal derailleurs I can find looks.

Can anyone tell me what I did wrong? My understanding is that the purpose of those pulleys is to take up slack in the chain. When I fixed my chain, I did end up shortening it, but it still looked like there was plenty of slack. Can a short chain cause this problem?

Any help you can give me would be greatly appreciated.

[nfmisso]

My GUESS is that the spring stop inside the RD or the spring broke.

I would replace the RD with this:
http://www.amazon.com/Shimano-Tourney-TX35-Derailleur-Speed/dp/B003ZMH69S/

And replace the chain and freewheel at the same time - that freewheel looks questionable.

Chains need to be properly sized; the instructions for the TX35 show you how; or search on the 'net for proper determination of chain length.

[DaveM]

Some of these derailleurs don't have a stop on them to prevent the whole pulley cage from rotating around and allowing the main spring to unwind. You might try removing the chain, then try to rotate the pulley cage counter clockwise one revolution before re-installing the chain. If I'm right, it should develop enough tension to keep the chain tight, but not so much that you blow the derailleur apart.

Otherwise, I think nfmisso is probably right and the spring either broke or popped out of one of its seats. May have to replace.

[nfmisso]

(04-07-2014, 01:03 PM)DaveM Wrote:  Some of these derailleurs don't have a stop on them to prevent the whole pulley cage from rotating around and allowing the main spring to unwind. You might try removing the chain, then try to rotate the pulley cage counter clockwise one revolution before re-installing the chain. If .....

Hi Dave; Great suggestion; I have not seen that one before, and it makes a great deal of sense. Hopefully this will be the case, and save the OP some cash.

[generic_cyclist]

Thanks for the ideas! I'll try them out this evening and see how it goes.

[generic_cyclist]

Update:

I know it's been several days, but I just wanted to say that rotating the pulley cage worked like a charm!

Thanks to both of you who replied. I can't tell you how happy I am that this was an easy fix!