take care when removing them not to let the little springs go flying! the gears separate and the top one fits into a little groove on the bottom one. it is possible to put them back together upside down, but not likely if you actually look at it closely.
now you are left with the center stem and spindle which lifts out after removing a small plastic crescent-shaped part. i am not sure what the correct term for this is, but again a fingernail or a small screwdriver will do to pry it loose from either end. this is the only plastic part, and care should be taken not to clean 