Front brake issue

I have stock disc brakes on my 69 B body. Just last week, the left front started "grabbing". Example, when driving 30 miles per hour, coming to a standard slow stop, with very little brake peddle pressure, the left brake will lock up. It releases ok when the peddle is release, but will lock up again if pressure is re-applied. And we are talking using very little brake peddle pressure. What are your thoughts.

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look close at the caliper and mounts, especially if it is a slider type caliper.
those types often get "divots" worn into the brackets, which causes the caliper to apply unevenly. this can cause different symptoms, including what you are experiencing.
the caliper piston can get somewhat crooked in it's bore, due to bad o-rings, also causing the issue you are experiencing.

Some simple diagnostic steps. From checking caliper to the flexible brake hose

https://www.youtube.com/watch?v=1Mor9N9Rv2w&t=0s

Check brake hose on opposite caliper. If that hose goes bad 100% of fluid goes to the good side causing it to lock up.