Mountain bike thinks 3rd gear is 1st
Yesterday, I bought a Diamondback Apex secondhand for $75. The man I bought it from said that it might need new tires and the gears could use some oiling, but that the bike was in good condition other than that. Seemed like a good deal, so I took it.
The tires just needed to be aired up, and the chain definitely needs to be lubricated or possibly replaced (kind of rusty). I decided to ride it a bit, and discovered that the gear shifter seemed to treat the third gear as first. Shifting higher than 5th gear causes the chain to come off. I played with the derailer and derailer cable a bit, but the best I could get it to was second gear. I have considered taking it to a bike shop for a tune up, but the nearest one is over an hour away. I've also heard that the problem could be inside the shifter itself, but I haven't tried taking it apart yet. Any ideas?