Why must car start in P or N and not D.

[ShadeTreeMech]

the clutch cable broke in a Chevy Spectrum I used to own. Thank goodness I knew how to shift without the clutch. I drove it from Colorado Springs to Denver (about 90 miles) without a clutch during a blizzard and had no issues. Driving in town was annoying, but doable.

Not having a safety switch saved me a bit of pushing the car once when my Datsun 210 ran out of gas. I used the starter to move the car about a mile down the road to a parking lot. It was funny finding out how fast I could go on just the starter and in 5th gear!

BTW when the starter engages on an auto, the torque convertor goes for the ride in any gear. In neutral and park, it's the clutches that are in neutral, and like others mentioned, at such a slow speed it's unlikely you'll get much drag from the convertor if in gear.

[ragez0r]

Originally Posted by wikityler

Why are cars designed so they can't start in drive? Is it just a safety thing so you don't start moving right away, or is there a more mechanical reason?

What I'd like to implement it an off button for use while at red lights. Something that cuts the engine when pressed, and starts it back up when released. Building such a device would be easy, I just want to make sure it isn't going to do any damage.

because remote starters would have comedic value ?

[dcb]

remote starters already have comedic value Best thing for efficiency and quick warmup is to start driving.

[comptiger5000]

In my mind, the only use for a remote starter is in really, really cold weather (below 0* F), you could start the car while you're walking to it if it's parked outside. This would give it about 30 - 40 seconds to get the cold fluids flowing by the time you got in and started driving. Otherwise, they're just a waste of gas, especially in something like my Jeep that probably sucks over a gallon an hour at idle (even warmed up).

[Imatech]

I think it was used as a safty device, for the people with coffee and cell phones.

[BLSTIC]

In the automatic speedway cars everyone bridges that switch so they can start if they spin and stall (yes it's possible). I started mine in gear many times intentionally and it never had any issues (without any gear selector indicator it was safer to start in gear than select the wrong gear for the race and have to change it on your way to the first corner with 8 other cars).

[Nerys]

well I had to kill a neutral kill switch once in an older car but that was because of a bad clutch. IE could not clutch to neutral so could not start the car or shift gear into 1st

so I disabled the switch put it in 1st and started it up. since this also MOVED the car as it was cranking (hence why the switch is their) I was able to get the car going and driving :-) (just had to get it down the street) you can clutchless shift and just turn if off to do it all over again if you have to stop.

a nice emergency way of moving the car if the clutch is hosed.

[Dr. Jerryrigger]

With newer AT's I have no idea what would happen. When I'm driving with the engine off, and forget, and down shift, it does nothing. It just stays in N. So I freak out a little and turn the key, but it wont start because it's still on 2nd or something. My brakes stop working when I drive with the engine off some times, down shifting is my instinctive other braking option, so I've done this twice... I keep the engine running now. But if it can be in 2nd and decide it should really be in N and then it was started, it could work out fine, or possibly really bad, but the torque converter is a good thing.

[ShadeTreeMech]

to nerys: i've had the neutral switch disabled in an aging Datsun once before, and was indeed able to move an extra mile to a better parking spot when I ran out of gas. I discovered I could get up to 35 mph using the starter and being in 5th gear!

to the Doc: if the engine is off, and you select a gear while rolling, normally nothing will happen because, without the hydraulic pressure coming off the pump which gets its energy from the engine, nothing can be engaged. However, beware of the lock up torque convertor trying to engage in such a situation. Bad things can happen if the spped is high enough and the computer send the signal to the convertor to lock up.

Otherwise, no harm no foul assuming the torque convertor remains unlocked. which is to say being in 2nd is safer than being in D with the engine off during a coast.

[dennyt]

Originally Posted by wikityler

Why are cars designed so they can't start in drive?

This was a result of the early 1980s Audi 5000 unintended acceleration debacle. It forces drivers to properly find the brake pedal before driving.

Autosafety.org

TheTruthAboutCars.com