Hi! I bought my first real bike (a 1980's Miyata Road Bike, pic at bottom) second-hand off some older gentleman. Been commuting daily since June. It has "Sora 7 speed" STI shifters, seem a few years old. So here comes the problem. It's kind of hard to explain, so let me just do an example of shifting into top gear.
Start in the highest gear, click once, chain sometimes decides to go into second, sometimes doesnt. Second click always gets into second. Third click, third gear. Fourth click, fourth gear. Fifth click, *clack clack* noise deciding between 5th 6th and 7th. I never know which one it'll hop on. Now everytime I upshift from say 4th to 3rd, I have to trim it each time, it never goes on perfectly.
When I switch into the larger chain ring in the front, it makes the chain/whatever scream, making a grinding noise.
So, which component is at fault? Is the derailer bent? Does it just need to be adjusted? Are my shifters and detailer not compatible? Is my chain not long enough? Is the rear cog's teeth too worn down/damaged? What components would be a good upgrade to buy to make riding smoother and more enjoyable?
Sorry for so many question, appreciate any answers!