Driveshaft
 

How do you know if the U-joint is bad in a driveshaft? How do you fix it?

Hold one side still and shake the other side. If the u-joint moves its bad. Hard to explain without having you see what movement is bad. Also, if it binds up or doesn't flex freely, it should be replaced. Or if it breaks(obviously).

So you're saying if I pick it up and it jiggles freely like a limp dick it's probably bad. :)