The pully & fan has come loose on my car.. How the heck do you tighten it back on? it has a nut and what appears to be either Torqux or an allen socket on the shaft. Any idea what size the center is?

Dont worry about the center of the shaft, put a socket on the nut and give her a crank. I've changed countless pulleys this way.

Tried that.. all it does is turn the shaft.. how do you stop the shaft from turning, in order to tighten the nut. Both the fan and pulley spin freely.. I thought there would be some teeth or something to grip the pulley.

I've always been able to clamp some vice grips on a fan blade, and turn the nut with a socket. Worked the last 100 times I did it.

well closer inspection revieled either a damaged spacer on the shaft or damaged pulley center. it whobbles up and down on the shaft. 'toast'. so I'll need to pull it out and replace the pulley and or alternator.. on thing is at least.. I'm pulling it off the road for the winter.. granted I could drive it for much longer becuase it'll be a while till snow arrives.. but oh well.

Well thanks for the quick help on the matter anyways.

Hmm, sounds a little different. Wish I could have helped you a little more.