I had a set of brushes lose contact with commutator on the armature while traveling halfway across the country in my '52. I took off the brush cover, reach my finger in and pulled the brush away from the commutator and let it snap back into place. I did this with both brushes and pushed the truck down the hill to start the truck with a dead battery, and it fired right up and the ammeter showed a serious amount of charge. I drove the truck 650 miles to the house.
I am surmising that the brush holder channel got dirty and would not allow the brush springs to push the brushes in as the brushes were worn away as they do over time.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission