they work fine on their own. they're called inline or interruptor levers, and people say that they push the housing instead of pulling the cable. that's confusing for me to think of them that way, because any lever does both (it depends on your frame of reference--think back to high school physics class). pulling the cable IS pushing the housing. it's a hinge and either the side of the hinge holding the housing moves, or the side holding the cable moves; it moves the end of the cable away from the end of the housing, and so the cable is pulled up again, down by the brake.

if the explanation was totally unnecessary, forgive me. it's good for me to spell it out, because i didn't really understand how or why they worked at first. but i'm a visual/tactile learner and need to explain things to myself in order to understand...