I'm not a big expert, so forgive me if I use some terms wrong (especially because I'm not a native English speaker).
I have a MTB with V-brakes. I wanted to tune the rear brake because it looked like the pad were working asymmetrically (with the right pad being closer to the wheel). What I noticed, though, is that the whole brake tends to "move" to the left, where the noodle is. If I pull the whole brake to the right with my hand then pull the lever, the right arm gets pulled while the left one stays almost in place; when I release the lever, the right arm stays in place and the left one gets away from the rim. After that, pulling and releasing the lever seems to affect only the left arm - with the right pad staying quite close to the rim, to the point that the wheel is always braking.
In short, if I understand it correctly, the brake arms should look like a V ( \ / ) and become parallel when pulled ( | | ); instead mine look like this ( \ | ) when released.
The bike has fourteen years and a couple of accidents on its shoulders (one affected the rear wheel, but I had it repaired at a shop, and AFAIK the rear brake was unaffected). Is this problem due to bad tuning? How could I fix it? Or should I forget about it and get a new brake?