yep just make sure the pullys line up correctly, after of course replacing the harmonic balancer ( good luck if you havent done it yet air tools will help ) might as well check the seals while your down there and if you can afforde it just replace them before they start leaking. oh and to why the car ran with a slipping pully, is pretty simple the pressure applied by the belts and the speed at which the main shaft turns actually will turn it, not very well but it will, eventually youll get no pull at all on it and it will fall right off.