If your planning on pulling it apart with the steering wheel hold down nut, you need to pull the shaft out of the column. The top bearing is held in the column by a screwed in plate and has a spring clip on the top side. Those things set the height of the steering wheel on the outer column. If you don't want tp take the column apart, you need to pull the shaft to extend it at the shear pins from the bottom of the column.

The force required to pull the two shafts apart isn't very high, once the pins have been sheared, but the fit isn't loose, it won't fall out by holding it vertically, you will have to pull it apart. A good thump on the bottom end will shorten the shaft though. The more often it gets pulled and pushed, the easier it moves.

I would not be concerned about locking the shafts into a specific position after they have been moved. There is not enough space in the vehicle for the shafts to come apart without major body damage. Once in place, the lower connection on the steering box is designed to float in and out, the odds of the inner and outer shafts moving isn't very high unless there is compression in a crash.

I recently had the same issue with my 1970 roadrunner. i took column out to do some work on it. when i went to install the steering wheel shaft was too short. it drove me crazy for days. i kept taking it out of car . it fit into coupler fine but something was not right. i finally realized i somehow collapsed the internal steering shaft. i pulled shaft out a little and put everything back. i now have no issues. i would not worry about the nylon shearing off. you will be fine without it



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Exactly: too many people become "fixated" about those "plastic pins"..

the only time i get concerned about the plastic, is when it totally deteriorates and falls out, creating slight play between the two tubing pieces.

Given that the plastic sits in a groove on the inner shaft with about a 1/16" space between the two shafts, that plastic would have to be in really bad shape to "fall out". If it did, a sloppy fit could result in sloppy steering response. That would be a very long shot chance, unless your pulling the inner and outer shafts apart very regularly.

Plastic pins?
BFD.....

Injection holes

Correcto !!! People think there are 2 pins going thru the shafts. There isn't.
Once the 2 shafts are aligned at factory, plastic is injected between the 2 shafts.
What is visible is just the remnants from that injection process.
If the shafts are moved afterwards, those 2 spots shear-away from the underlining plastic
And, may or may not fall out of holes.
That's why measuring overall length is the ONLY true determination.

My point was....If the plastic breaks, so what? I've had it happen on several columns with no ill effects, no vibrations or slop.

Agree completely,

Thanks so much for all the advice and information, very helpful. I also did a lot of other looking around. To cut to the chase - I've now fixed the issue
So basically I removed the column and did a lot of measuring etc, then just separated the key housing (which is attached to the shaft) and pulled that out as far as I could to take a look. I was able to confirm the measurement from the top of the shaft to the first pin was about 2.5" shorter than expected. So I held the bottom of the shaft in my vice (suitably protected), made a bracket for my slide hammer, and pulled on it. To address an earlier comment, this would cause no damage because the rest of the column is not connected to the shaft. you are literally pulling one end of the shaft from the other. I double confirmed this by separating the top of the housing as mentioned.
I needed some pretty serious pounding to move the shaft. I basically had to bite the bullet! I could see that the shaft had moved as a result but had to go back a couple of times to measure and pull again. Eventually I measured and appeared to be at exactly factory length (a bit of judgement and quite a bit of luck). You can see in the 'after' photo the part of the shaft that had collapsed by looking at the surface rust marks.

With it taking so much force I was not worried about securing it further. If I was I would have used Loctite 660 which was basically the factory 'repair' method.
I took it to the shop finishing my car for me to do a trial fit, confirmed it was spot on, then took it home, finished reassembling, and a couple of days ago took the column in , fitted the coupler, and properly fitted the column.
So I'm happy with the result after a bit of an initial shock, still a mystery how the shaft shortened after I removed it and took a lot of care, but it is what it is. It took longer to research it than to actually fix it, but did not want to take any chances.

By the way, I agree with the discussion about the nylon ring and the 'shear pins' really being injection holes, but the factory does use that exact terminology. Regardless I just don't see the 'pins' doing much of anything, and in all probability had already fallen out on mine long ago. It's the nylon rings providing that (considerable) resistance

So thanks for the advice, I thought I should at least provide a conclusion which might help someone in future!

Refitted!!