Here's what I did. First, I didn't have a 450 so mine was a little different but the mechanics should be the same. First, determine if the shaft comes out the front or back. Mine came out the front. I remover the "can" from the motor and then removed the clip from the rear. Next, I found a piece of hard wood (oak in my case). I drilled a small hole the size of the shaft in the block of wood. Next, I took a nail the same size as the shaft (could even be a little smaller but not larger) and cut off the end so I had a flat surface. A Dremel toll works good to give a flat surface. I then inserted the motor shaft into the hardwood so that it was just below the surface of the wood surface. Make sure of the direction. Your are going to drive the shaft out of the wood block. On my motor I inserted the rear of the shaft into the hole in the wood since I was going to drive the shaft out through the front of the motor. I then took the nail and placed it in the hole in the wood so that I was in contact with the shaft. I placed the motor on a vice so that the vice supported only the motor face . A few light taps with a hamber and out came the shaft. To insert the new shaft I just reversed the process.

I hope this makes sense.