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When one wants to park a manual transmission (MTX) vehicle, one puts it in neutral, and engages the emergency / parking brake. With an ATX vehicle, the practice I've learned is to put it in Park, and engage the parking brake.

But if I need to engage the parking brake, then what exactly is the purpose of selecting Park? What does selecting Park do and how does it differ from selecting neutral?

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It may be different in countries that still sell a good number of manuals, but here in the states, I've never met anyone that puts an automatic in park and sets the brake unless they're on an extreme hill. – JPhi1618 Feb 3 at 13:52
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@JPhi1618 I park with the transmission in park and pull the brake every time. Belts and braces: I really don't want the car moving at all until I'm ready. – Bob Cross Feb 3 at 15:55
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Umm, I put my manual transmission into gear when parking, not neutral. – Ellesedil Feb 3 at 18:51
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Like @Ellesedil said, you don't want to park in neutral. In general you want the lowest gear available in your transmission to maximize the engine breaking. Some cars (looking at you Saab) won't even let you take the keys out of a manual transmission unless it is in reverse. I learned in a Saab and still put everything into reverse since it is usually geared lower then 1st. – Ukko Feb 3 at 22:53
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@ChrisH everyone I've spoken with (in a country where manuals are the norm) do what I do, which is to always start the car with the clutch depressed. If you make that the habit, rather than relying on the behavior of the previous driver, it doesn't matter what gear whoever drove the car last leaves it in. – Alex Feb 4 at 9:39
up vote 37 down vote accepted

In an automatic transmission there is a ring with teeth on the output shaft of the transmission. When the transmission is shifted into park a lever called the parking pawl is lowered against the ring. If the parking pawl did not land squarely into an opening in the ring the car will roll slightly and there will be a usually an audible click. The parking pawl now holds the output shaft from turning.

Automatic transmission showing parking pawl

Without the engine running an automatic transmission is effectively in neutral in any gear except park. Theoretically with park engaged also applying the parking brake is not necessary unless the car is on a big hill because the parking pawl has more than enough strength to hold the car from rolling. It is a good idea to exercise the parking brake on a car with an automatic so the system does not freeze up.

PS. In a manual it is suggested to place the car in first gear or reverse then engage the parking brake and for good measure curb the wheels. In the event that the parking brake fails (more common than the parking paw) the engine with the sub one gear ratio will hold the car. The good measure of curbing the wheels will roll the car into the curb in the case that the engine can't hold the car from rolling.

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14  
Love that picture - thanks. The pic can also be interpreted as: This little piece of metal is the only thing holding your 4000lb car in place. – JPhi1618 Feb 3 at 16:07
    
@HandyHowie Thanks I fixed it. – vini_i Feb 3 at 17:27
    
What vehicle is this chain-driven transmission from? – Digital Trauma Feb 4 at 1:39
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@DigitalTrauma - The image appears to be a screencap from this video. At 0:40, he says it's a FWD Ford 6F35, so there are several vehicles it could be from, though he says it's from a Ford Escape in the comments. – Compro01 Feb 4 at 3:23
    
If you accidentally put the trans in Park while rolling, the pawl will not engage, it just makes a lot of racket and you go "Doh!" I did this once when I saw my brother's car ahead of me get hit by another car. I was so startled I got confused and didn't stop correctly. – no comprende Apr 21 at 4:01

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