Best rear derailleur for a Schwinn ranger? A few days ago the cog on my Schwinn Ranger rear bike derailleur broke in half after changing gears.

I examined the cog and it was made of flimsy plastic. Was wondering if I could put a new/different rear derailleur on there for this same make and model but of higher quality, with metal cogs.

The bike derailleur that was on there before was a Shimano tourney tx which go for about $6 online. Want to upgrade but not sure how to go about it or what is the correct ratios and such for it.

I know with car parts everything has to be in accordance with the brand and specs. What rear bike derailleurs would be the best fit for a Schwinn Ranger? 21-speed.
Any Shimano rear derailleur designed for 7 speed (3 front x 7 rear gears =  21 speed) drivetrains and mountain bike gearing will work.

For your practical purposes, the compatibility chart from Shimano below gives part numbers for the available rear derailleurs which will work with a 7 speed MTB drivetrain: 



Those part numbers can be specifically matched for each derailleur.

To break down the part number I will use RD-M360 as an example.

"RD" = Rear Derailleur - "M" = Mountain Bike - "360" = model ID number
"RD" = Rear Derailleur - "TX" = Touring Bike - "800" = model ID number


Typically, the higher the model ID number, the better quality the part.