Technical Spindle snapped this weekend.

Did the lady have any good stuff to look at in the late husbands pile

 

Wow! Very close to a really bad accident. Low speed failure, close by, you have parts and ability.
You were very blessed!

 

Your 1964 ElCamino did not originally have front disc brakes. Many of the common disk brake upgrades require either machining the upper boss of the drum brake spindle for the caliper bracket or changing to an aftermarket spindle made for the caliper bracket. I suspect the quality of these aftermarket spindles may not be as good as the OEM spindles. As others have said, that is a classic fatigue crack, probably starting at a sharp notch, and probably influenced by poor metallurgy and heat treatment.
Glad you didn’t have it break at highway speeds.