Bike didn't shift into all gears
I was trying to fix my sister's bike, which could only switch between 4 gears in the rear. I read in Zinn and the Art of Mountain Bike Maintenance to tighten the rear shifter cable, which I did. This only changed the 4 gears between which I could shift. I ended up taking it to my LBS, but he didn't want to share his secrets. How did he fix it?