I have inherited two g-body differentials, one of which is rust free and has new backing plates, but the side gears have been destroyed. The other is so rusted out that the axle tubes could fracture. My plan is to transfer the side gears of this one to the other. I have removed the pinion shaft bolt on both and it is an 8mm about 1/2" long. The pinion shaft is still locked in place. What am I missing??

 

The rest of the broken bolt that's still in the hole.

The pinion shaft lock bolt is about 1.5" long. This is unfortunately a common problem and there's a kit available to get the rest of it out. Or, do what I did and grind/drill into the end of the shaft until you get to the remains of the lock bolt, at which point you should be able to get it out. New shafts and bolts are readily available at the GM dealer because this is such a common problem.

 

Thanks for the info Joe, they are both out!! I did not use your method but checked out the kits. Cheapest I could find was $25.00. Being of Scottish descent, every penny is a prisoner. I looked at the pix of the kits trying to figure out how they worked and ended up making my own. For anyone else reading this, I took a 5/16-18 bolt 3/4 '' long and drilled it through the center, on the length. Started with 1/8' and went up to 11/64". Turn this bolt into where the pinion shaft lock bolt was and snug it up against the broken piece that is inside. This prevents the broken piece from turning. Remove bearing cap to allow access. Using 12 " long 1/8" drill bit, pass it through the 5/16" bolt and drill about a half inch into the broken bolt. Remove the 5/16" bolt and lightly tap a 9/64" drill bit into the hole you have just made in the broken. On one of mine I was able to simply pull out the bit with broken piece attached. The other I had to turn out, but had to start the turning with the help of a vise grip.
Total time to make thread protecting 5/16" guide bolt and removal of broken locking bolt was about 30 mins. Total cost $10.00 for the 12" drill bit.
Hope this helps someone else.