MOPED ARMY

i am having clutch problems on a tomos w/ a-3 engine. what i was wondering is how do you tell when the clutch goes bad, and i know you can tell by it not shifting, i mean are there visible signs. the pads look fine and the spring as well. however when i took a working clutch out of another a-3 and put it in when i started it all it did was shake and almost jump from under me. any help would be appreciated. thanks