Originally posted by: RayH
I'm guessing the odds of a car rolling on its own on a level surface with a properly functioning parking brake are lower than having somebody bump the car especially if you live in a city where "braille" parallel parking seems to be a common practice. I don't think "Park" on an automatic has any direct parallel on a manual. If one truly wanted to use the engine for braking, why not use 5th or 6th gear instead of 1st? I admit, I do put the car in gear when parked on a hill but any other time it's in neutral.
I won't deny the common (and hit-and-run illegal) practice of "braille" parallel parking. However, having someone bump your car when it is in gear will not damage the transmission, they're built much stronger than that. Just think of the forces placed upon the transmission just to start the car moving, or to shift gears, or (in the extreme) to drop the clutch at a given high rpm and do a burn-out. A "bump" is nothing compared to those.
"Park" in auto is different than anything in a manual as it uses a pin known as the parking pawl to hold the car in place. This is because otherwise an auto trans does not have a direct mechanical connection from the engine to the wheels, which a manual has inherently.
One puts a car in 1st for engine braking (and not a higher gear like 5th) because in 1st the engine exerts torque upon the tires. In an overspeed (ratio less than 1) gear like 5th, the tires exert torque upon the engine. In simple English, in a single given linear distance of tire roll, the engine will spin farther (usually 3-4 times farther) in 1st than in 5th, which means there is more engine compression force upon the tires in 1st than in 5th.
You should always park your manual trans car in gear (and engage the parking brake), regardless of the circumstances. It will not damage your transmission and it does not take any extra time or effort. It's just simple common sense and safety.
Someone mentioned out one could forget that the car is in gear and forget to depress the clutch when starting. I can't think of anyone who has owned a manual for a long period of time doing this. Personally, I have owned nothing but manuals for more than 15 years, and checking the car's gear and depressing the clutch before starting is second nature. I never forget and I don't even think about it. So much so, in fact, that I often bang my left foot on an empty floorboard when I drive an auto.
