so i got this bike about 2, maybe 3 years ago. i bought it for $250, pretty nice deal i think...
anyway, it's been acting up lately:
*the back gear sticks on 7
*the brake rubs hard against the rim--its actually been doing this for awhile, just not as bad as now
*and a few other things i cant remember
i've fixed the gear problem before, but my "method"--if you wanna call it that--just hasnt worked the past few times i've tried it. i've also done everything my tiny brain can possibly come up with for the brake.
all the other problems i know i can fix with just new tires and repairs.
If the rim hits the brake pad in the same spot(s), the wheel may be out of true:
If you tighten a spoke nipple, it will pull the rim to that side of the hub, so you want to tighten the nearest spoke or two which goes to the side of the hub opposite the pad that rubs. You can use your brake pads as a guide for minor truing, but if it's way out of whack and/or you don't have a spoke wrench and/or you don't know what you're doing, take it to the shop. If you go w/DIY, don't forget you have to turn the spoke wrench left to tighten and right to loosen.
If it is one side of the rim that constantly rubs on a brake pad, then the brakes probably just need to be centered. I assume your 820 has linear pull (V) brakes. On the side with the rubbing pad, you'll find a little screw on the brake arm near the pivot. Tightening it will pull that pad away from the rim. If it's already in pretty far, try loosening the screw on the other arm.