I bought a Trek 820 off craigslist. I paid $65 and it's barley been used. It's a few years old. It's the first "real"/not Walmart bike I've ever owned. Also the shifting is different can someone explain to me how the shifting mechanism works? It feels like I can gear up, but not down. It's not a 2014 model. I know it's at least 5 years old and I can't find this information anywhere. Pictures will be attached below:
There is an identical mechanism on the left side
^ That is back side of the mechanism.