My memory failed me, his profile says Ontario.
hangs head in shame
Let’s not start that! 
Anything using a fluid torque converter - which is nearly everything before about 2000 and still some good percentage of larger vehicles - is not going to have as strong a tranny-to-engine coupling as the reverse. There are various controls on newer cars that will keep the engine speed up in such circumstances.
Most newer, smaller and higher-performance cars have anything between very tightly coupled fluid converters, locking converters or automatic clutches. The engine and tranny are coupled almost as tightly as in a manual-shift vehicle, and downward coasting will drag engine rotations with it.
Any discussion of what happens on downward coasting while in a “drive” gearshift position needs to consider the differences.
I was talking about restarting an engine in a car coasting downhill with a conventional automatic transmission there. Whether you’re in gear or not, I was agreeing with Nitro that you’d have a lot of slip through the transmission there, so in gear is closer to being in neutral, or somewhere in between. In a standard transmission you’d have a direct link from wheels to the engine through the drivetrain. That’s all about older automatic transmissions though, not modern cars.
Thanks for clarifying.
That practice seems like you’d only use it in weird emergencies, if even then, since it seems like it would wreck trannies.
I tried it ages ago, just to see what would happen. I’d heard conflicting information about whether or not you could push start a car with an automatic transmission. My experiments showed you could, but you had to be going more than 30MPH. You can push start a standard at around 10MPH, maybe less.
By ‘push start’ I mean popping the clutch while the car is moving with a standard transmission, or shifting into drive with an automatic. I think Nitro’s explanation makes sense, the fluid clutch wouldn’t lock up at low speeds, and was probably designed not to convert that much of the backflow through the fluid clutch (which was usually a torque converter).
ETA: Anybody remember what you call that extra part in a torque convertor inbetween the impellor and the (what do you call the other thing? A turbine?). Jeez, I need some caffeine.
Yeah. Please.
That’s not right. On automatics built since the early 60’s or so, you can’t roll start them no matter how fast you get going. That’s because there’s only a fluid pump on the input side of the tranny. You can get the output side spinning as fast as you want, but it’s never going to build pressure and transmit any rotations to the engine. Earlier automatics that could be roll stared had a separate pressure pump on the output side.
In the example of coasting downhill, though, because the engine is still rotating and running the fluid pump, the transmission will keep sending power from the wheels to the engine (even if the fuel injectors or even the ignition are off).
The car I tried it on was late 60s, 68 IIRC, so I gues that fits into the ‘or so’.
What kind of car was it? Did you actually go from engine off/car stopped at the top of the hill to starting it on your way down? Like I mentioned, that shouldn’t be possible on any but some of the earliest automatics. If you put the car in neutral and then kill the engine while you’re already on your way down, I know sometimes the residual pressure or locked torque converter will allow you to restart the car by just putting it in drive, but roll starting from a dead stop shouldn’t work.
Something with a Powerglide? I think they kept the output pump until sometime around then.
It was from going downhill. It was a big Buick Skylark wagon. I don’t know if it had powerglide. Even at speeds too low to start you could feel the engine braking after putting it in drive. Nobody was going to help me roll start that beast from a dead stop.