Owners manual says towing (or presumably coasting) a 6-speed auto trans to start the engine won’t work and will damage transmission. Why?
Because there is no mechanical connection between the engine and transmission.
If you tow/coast the vehicle without the engine running, the torque converter in the transmission isn’t turning,
And if the torque converter isn’t turning, the transmission pump isn’t turning.
But the rear wheels turn the drive shaft which turns the gears in the transmission, even in neutral. And without the pump turning in the transmission, the transmission burns up.
THis has been true since the 50s, my 56 Desoto was the last automatic transmission equipped car I could tow start.
I recall that the old Hydramatics could be push/tow started, but I’m not exactly sure when that feature disappeared from those transmissions. It is possible that Hydramatics retained it into the '60s.
Well, it happened when they took the rear pump out of the transmissions. I don’t know when that was for each make but most of my friends had GM or Ford products and were surprised my Desoto could be push started.
I had a 54 ford auto that could be push started.
The feature that enabled push starting an automatic was that it had two oil pumps, one driven off the transmission input shaft, and one off the output shaft. The “dual coupling hydramatic” (1956-1964) was the last one with a rear pump. The transmission in your DeSoto ( powerflite ) retained a rear pump until it was discontinued after the 1959 model year.