First of all, I have a lot of information on Corvette steering systems of the same vintage as your Chevelle. Saginaw Steering Gear made all the steering columns for GM in that era. Saginaw did a great job of standardizing components. A Corvette tilt and telescoping column is just a glorified tilt column. Standard (non-adjustable) columns had a lot of common parts. So a lot of Corvette parts probably fit a Chevelle.
Here is my best analysis of your problem. When you rotate your ignition key, you rotate a small plastic gear inside the steering column head. That small gear engages a small die cast rack. That rack slides up and down pushing and pulling on the rod that actuates your ignition switch.
I think that your rod is disengaged from the rack because the die cast rack probably broke. The bad news is that you will have to tear your column apart in order to get at the rack and take a look at it. There are complete instructions on disassembling your steering column posted at
Download all of the instructions (either the Std Column or the Tilt Column). You will need all of the instructions under the appropriate type steering column. They will assist your in pulling the column out of the car for a teardown.
Standard (non-adjustable) columns are very different from tilt columns. So here are two approaches depending upon your type of column.
If you have a standard (non-adjustable) column and you determine that the rack is broken:
I don't have any Chevelle supplier brochures so I can only give you some ideas on Corvette parts that might work. Hopefully, you have some sources for equivalent Chevelle parts.
There is a Corvette supplier by the name of Dr.Rebuild. He has a ton of old parts. Just don't **** him off. He won't sell to you if he doesn't like you. (Again, assuming that the rack is broken). Looking at his websight I find that there is a rack & rod assembly for standard Corvette steering columns:
rod & rack 2187440
The problem is that there were different length rods depending upon the GM car lines. I don't know if the Corvette rod & rack is the same length as the Chevelle or not. (I am equally sure that Dr.Rebuild won't know either). If you have a standard column there should be an equivalent Chevelle rod & rack assembly. Hopefully a Chevelle supplier can get you the correct part. Otherwise, you might have to take a stab at the Corvette part. Or find a junk Chevelle standard column and tear it apart.
If you have a tilt column and you determine that the rack is broken.
The Corvette T&T rack is available from Dr.Rebuild
Ignition Switch Actuator (toothed rack only) 2187426
This rack I am pretty confident will work in a Chevelle tilt column.
Tilt columns had a actuator rod with a small casting with a pin on it to engage the rack. If the problem is that part, you will have to find a Chevelle tilt column part to fix it because I just don't know if the equivalent Corvette part is the correct length.
Continue posting on your problem and I will see what I can do to help.