I've seen this one time (in my life) and one time only and it was a freak failure. The year was 1981 and I was going to auto tech school. We were allowed to work on cars owned by John Q. Public.
A guy had his car towed to the school one Monday Morning for us students to fix. I remember (for some reason) that this was a full-sized GM car. I suspect your Chevelle probably uses the same gear box.
Anyway, at church parking lot the previous day, his steering gear had a a catastrophic failure. The end of his steering gear blew out the side and his steering wheel quickly jerked as far left (or right, don't remember) and he couldn't hold it.
The steering gear assembly was literally in several pieces. We fixed it by putting on a junk yard donor part.
Just one of those freak failures that was lucky to happen in a church parking lot and not traveling down the highway at 60 mph.
Not to scare you or anything and the odds of this happening are nil, just thought I'd pass this on.