Bicycle Mechanics - Rear derailleur arm is too high up

Hello,

I recently attempted to do some maintenance on my bicycle which resulted in an unexpected problem. I tried to remove the chain for cleaning by pulling on the rear
derailleur arm to reduce the tension on the chain and make it easier to remove. I eventually had to use a chain tool to remove the pin to get the chain off of the bike. After cleaning the chain and putting it back on the gears, I notice there was a lot of slack in the chain, and that the rear derailleur arm was very high up. It has to swing down (counter clockwise) about 150 degrees or so.

I am not sure how to adjust the position of the derailleur arm so that I can get the correct chain tension again. Does any one have any useful links or suggestions for me?

Thanks a lot

greese_monkey: A picture would help but from your description it sounds like you re-threaded the chain improperly. From the top of the front chainwheel it should run over the back of the cogs, over and in front of the upper jockey wheel and behind the lower one before heading to the bottom of the front chainwheel. Google "thread chain trough derailleur image" for some pictures. Here's one way to do it: http://www.livestrong.com/article/487240-how-to-run-a-chain-through-the-derailleur/

Based on the description, I'm guessing the arm got past its stop and is now in the part of the swing it would never ordinarily be able to reach. Some people just brute-force the arm back past the stop the other way, but if you want to be kind to your derailleur, you can also do it the "official" way. Park Tool has some helpful pictures here: http://www.parktool.com/blog/repair-help/rear-derailleur-overhaul Scroll down to Shimano derailleur overhaul and look at photo #4 for the stop I'm talking about.

Hi dsbrantjr,

thanks for you quick response. I have added a picture of the rear derailleur as an attachment on my original post. From reading through the webpage that you sent me, it sounds like that is the problem. I'll try that and let you know if it works.

Thanks a lot.

greese_monkey: Yes, it is definitely threaded incorrectly. The chain is going onto the cog from the wrong pulley in the wrong direction. Follow one of the online procedures and you should be OK. Keep in mind that the upper pulley does the shifting by guiding the chain onto the correct cog and the lower pulley takes up the slack in the chain. Best of luck.