Steering Column Repair: ignition lock cylnder, model gm, lock cylinder

Question
i have a 1972 chevelle and can not get the lock cylinder out i do not have keys to it and have a new cylinder tryed every thing so far still in coloum

Answer

There is a groove in t Hi David:

The early model GM lock cylinders a re a little different than the 80's and 90's.  If you have a replacement lock, you will see a small black spring loaded bar on the side of the cylinder housing.  that is what holds the lock in place.  
to remove it, most times you need to punch through the cast housing in the correct spot to depress that bar.  Once you press the bar correctly, the lock simply slides out.  the new one will slide in and lock in place by itself.
Here are the instructions and a picture to help you accomplish that.
Let me know if you have any more trouble.

Good Luck
Doug