today I bought a remaned vaccum pump. Pulled the old pump and was going to install the pulley on the new pump. The pulley falls onto the new pump! I have changed several vaccum pumps on GM and Ford trucks. All the shafts I've seen were the same size, till today. Anyone got a clue? The OReilly part number is 64-1009, supposed to fit an 89 GMC G25 Ralley STX A/C with a 6.2. What AC has to do with it is a mystery to me also. The worst part is, no other OReilly in the area has one. It sure ruined my day. It is 55 degrees here, perfect for working outside. Thanks. Mike