Does the pedal present any resistance at all or just go easily to the floor? No rsistance sounds like a master cylinder problem, a hard pedal with little assist may be a booster. You are on the right track. With the wheels off the ground, spin a wheel and have someone press the brake, continue to try and push the wheel if it stops and have them release the pedal to make sure the brakes release and the wheel spins immediately. Does the right wheel stop at all now, or has nothing changed?