So another question has come to mind. I've ordered the 5603 shifter, will that be compatible with my current derailer, which is an fd-5504? Or will I need to replace that with a 5600 series derailer? Thanks again for any help! I've never serviced a bike before, other than changing tires, so I'm learning as I go here. I know I could just take it to a local bike shop, but I'd much prefer to learn how to work on them myself.