i used to have a 91 legacy with a 2.2 liter, (i think), the harmonic balancer came apart when i changed the timing belt. when i went to get a new one i was asked if it was and automatic or a manual is there a difference in weight? i put one off of a manual because it felt lighter or was it just the pepsi talking?

Yes there are different weights. Auto trans typically uses a heavier balancer to help smooth out engine vibration at idle. If the car has more than about 100k miles on it you won't notice the difference.