1994 S10 Blazer 4dr, 4wd, just over 100K miles.

My son just came home and said his Blazer is making "some noise". Took it around the block and its sounds OK until I put it in 4wd, then a horrible clunking. I get it home, jack it up (hoping for a broken CV) and find that the front yoke is very loose. Anyway its 15 degrees here today and the driveway is snow covered, so I tell him to drive it in 2wd only until I can look at it closer. What would cause this to come loose? What kind of a nightmare am I looking at to fix.
Thanks for any insight.

 

I've had rears come loose before, but not the front. I would just re-torque it and go from there if I were you.

 

I have a bad feeling the whole shaft is loose due to a bad bearing. Any chance the bearing can be replaced from the outside, or do I have to open the TC?