My rear brake isn't functioning right. There is proper tension in the brake line and I replaced the pads, so I think that there is grease/oil on the metal where the pad hits. What is the best way to clean it? Or have I misdiagnosed?
The primary question is whether the adjustment was done right. If that's the case, did you "rough up" the pad surface with sandpaper? It would be good to double-check your work.
If you did get grease or chain oil on the rim surface, a simple degreaser works well.
Why is it that they make adult bikes that'll generally work for 5'9" or above, yet when you pedal these same bikes they only work for someone who is 5'4" or so?
I like to clean the braking surface of my rims with rubbing alcohol and superfine (0000) steel wool. Dampen a small pad of superfine steel wool with alcohol and clean any brake pad or other residue off the rim. Wipe the rim dry with a cloth. Make sure to use superfine steel wool -- it won't scratch or score the rim but more coarse steel wool may.