Originally Posted by patentcad

I've been riding race bikes daily for 20 years and I've never even heard of what happened to my rear wheel this morning ever happening. The freewheel mechanism on my rear Williams 38 went into vapor lock descending a hill and sucked the chain into the rear wheel. Turns out the bike was rideable, but it was difficult. Like a fixed gear except you can forget to pedal, particularly on downgrades, and then you get near-instant terminal chain suck. I rode back west about 5miles (concentrating hard to keep the crank spinning on the long downhills, partially riding the brakes) and Mrs. Pcad came and drove me home. Then I swapped wheels and rode another 45 miles.

Probably a vapor locked free hub pawl. I have a spare free hub.