I'm new to the cycling world. I currently have a 2004 trek 1000 with a 3x8 setup. It is a solid bike and I'm looking to upgrade to a set of shimano sora 9 speed shifters because my shifters are old and need replacing. I believe I've done my homework on what I need but I'm looking for some extra input. I Am all set to buy shimano sora 9x3 shifters and 9 speed cassette. From what I can gather spacing will not be an issue. I just had the rear derailleur replaced after the original one broke. It is a shimano sora, and my question is will that derailleur work with a 9 speed cassette or do I need to purchase a new one? Thank you for any input. (Yes I know many may say "just buy a new bike" I intend to later on but money is not plentiful enough to do that right now)