I had the unfortunate luck of being the owner who gets to figure out what to do when the pedal crank on my old Peugeot road bike snapped in half while riding. After some luck in finding the right part, I've set about getting the rest of the bike back in more suitable condition.
The first step is figuring out what was the issue with the rear derailleur. For a short while before the pedal had its moment, the derailleur really only worked when pedalling forward and would jam the chain mechanism when trying to pedal backwards. This made me suspect the spring, but to find out I needed to do a little disassembly.
Removing the shift assembly¶
Accessing the pulleys¶
As part of the process, I found an ingenious little hack for not losing pulley parts: The inner diameter of the pulley mechanism exactly matches the outer diameter of a Presta valve from an inner tube that I'd popped (but kept around just in case it was useful, isn't that handy).
Here's a better picture of the mechanism now that it's a little more exposed (although all it seems to be exposing is dirt and some rust)
Found the Problem¶
Videos coming soon!
After a little wrenching, it was easy to see why things weren't working. The spring that keeps the mechanism aligned with the frame had snapped at one of the legs.
Cleaning¶
The first round of cleaning the derailleur involved a heavy use of degreaser and a scrub brush (and making a mess). It's a little hard to see in the photos, but there was gobs of grease and junk coming off the derailleur as I was disassembling, but there was still plenty more ready to scrub off. The end result looks fairly nice and cleaned up; however, it revealed some rust that I'm going to clear out in round 2.
Onwards!¶
In the next few days I'm going to take a pass at cleaning up the rust and finding the right spring to replace the broken one now that I can match it to parts easily. In addition, I'm thinking I may replace some of the rusty screws with new ones while I have the mechanism apart. One thing I'm not sure on is the bushings for the pulleys. It seems like they're in acceptable condition, but if I can find some drop-in replacements I may swap them out as well.