Eli5: how can you roll start a manual vehicle but not an automatic vehicle?
In: Other
A manual transmission uses a clutch to physically connect and disconnect the engine to the transmission. If the clutch is engaged and the transmission is in gear, when the engine turns the wheels will turn. Also, if the wheels turn the engine turns. That’s how you do a roll/push start. You use the rolling wheels (with the weight of the vehicle) to turn over the engine, performing the same function that the starter does when you start the engine normally.
An automatic transmission uses a torque converter, which is basically a fluid pump, to push the automatic transmission fluid through the transmission to deliver power. Effectively the automatic transmission is a one way connection, the engine can deliver power to the wheels, but the wheels can’t deliver power to the engine. This means the engine and the wheels can turn independent of each other, even when the transmission is in gear.
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