Am working on a friend's BMX brake. I believe it to be what is termed a U-brake. There is a small, maybe six-inch loop of cable that goes through a shoe of some sort that is pulled by a longer cable from the lever.
When I disconnect all cables from the caliper, one arm pulls away from the rim and the other arm towards the rim. I cannot fathom how that can be correct behavior. Basically, one arm's natural position seems to be in the very same direction that the cable must pull it in order for the bike to stop.
So am looking for a clue, so that I can get the kid's bike back together.
not sure about these ubrakes/990s, but often they have a washer with wrench flats through which goes the mounting bolt to the stud on the frame. This washer can be turned either way to set spring preload for each arm. Try rotating those to set the spring preload (and later balance)- the left one goes clockwise as seen in the pic below to add spring tension and the right, counter-clockwise. I have a feeling this kid had "righty tighty" stuck into his head and turned both the same way.