So, I have a ten speed 1979 Schwinn Continental II that I picked up for 25 dollars. The bike started fine with all the gears and components working, but the rear brake was squeeky. I replaced the rear brake, and when I put the wheel on I must have messed something up in the rear derailleur because then it wouldn't go into the lowest sprocket. I read about it a bit online and tried to mess with the rear derailleur. Now, I am stuck being unable to shift below the 3rd sprocket. I was wondering if anyone has any advice on how to fix it. Thanks!