To clarify the information in the above posts, the steering column itself is not collapsible. The intermediate shaft is collapsible. The thread linked below provides more info. Also, as noted above, this was a safety feature to reduce the risk of the column spearing the driver in a frontend collision, and the intermediate shafts in the 67s and 68s were one piece.
http://67-72chevytrucks.com/vboard/s...d.php?t=309895