tony,
Sounds like a bag of worms. In the Chevrolet, that "pin" I believe is actually a long hex headed screw. Could someone have broken the screw off, and in an attempt to maybe drill it out, broken a bit off in the hole?
If you put bearings and seals on, it means you must have removed the "pinion gear shaft" (looks like a king pin) to access the clips in order to pull the axles....right!
So now I'm not sure what's going on. Unless GMC uses a pin, this should be a small bolt. It really sounds like this has been broken, and then attacked with a drill. Clean the hole with brak-kleen, grab your trouble light and magnifiers and see what's going on.
My picture shows this as a blind hole...not somewhere you usually drive a pin into! I don't know the size, but I will bet someone on this site does..maybe wrenchbender...keep your fingers crossed.
Stuart
