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I am new to driving A/T cars and I am trying to understand the use of Neutral(N) gear. Should I shift my gear from D to N when my car comes to a complete halt on a red light or somewhere else? As per my understanding, putting brakes on while waiting on a red light while your gear is in D can damage the braking system?

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6 Answers 6

up vote 8 down vote accepted

For general driving, you can leave the car in drive. It doesn't damage the transmission leaving it in drive while stationary at the lights - although you don't want to be doing silly things like revving the engine while holding the brakes on.

In an automatic car, you don't really use neutral. It is a step on the way to selecting Park, which means that the transmission is disengaged.

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I'd say that "Neutral" is on the way to Reverse where the transmission is disengaged. On the way to park, you still have to go through Reverse, which reengages the transmission. Correct? –  Jesse Apr 3 '13 at 20:13
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@Jesse, yes, you're correct. At the same time, so is Rory. If you're shifting to park, you're almost certainly motionless (or about to learn a valuable lesson). So you're going to shift from D to N to R to P. –  Bob Cross Apr 3 '13 at 22:55
    
Shifting to park while moving, at least on some vehicles, is a viable last-resort when your ABS decides not to engage the brakes and you're about to crash into another vehicle... –  R.. Apr 4 '13 at 19:25
    
@R.. Last time I checked my foot engages the brakes not the ABS system. ABS should prevent lockup how is throwing into park going to do anything beside lock up the wheels and damage your transmission in the process? –  Mike Saull Apr 4 '13 at 22:39
    
I've only used the technique once, more than 10 years ago. The pavement was really wet and I didn't realize at the time but my left wheels were on a steel joint rather than pavement, and when I pressed the brake, the ABS kept detecting lock-up and releasing it (despite the fact that the right-hand wheels could have stopped the vehicle). Putting the transmission in park stopped the vehicle almost instantaneously. It did fail badly about a year later, but I'd rather have a failing transmission than have rear-ended somebody at ~25 mph. –  R.. Apr 4 '13 at 22:52

The main purpose of neutral on an automatic is for towing or pushing the car. Obviously you can't push it with the transmission in park, and if you tow it with the transmission in gear or in park and the drive wheels are in contact with the ground, you'll ruin your transmission or your tires or both. I'm sure there are some other uses too, but they're sufficiently rare that they probably don't need to be mentioned.

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Don't forget automatic car washes. –  BigHomie Apr 4 '13 at 19:16
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It should be noted that automatic transmissions are lubricated by a pump which only runs when the engine is turning. Long distance towing with the drive wheels on the ground will cause damage, even in N. –  mattmachine Feb 7 at 22:52

putting brakes on while waiting on a red light while your gear is in D can damage the braking system?

In general, no, you're fine.

I think you've conflated several issues that can lead to issues (if not actual problems):

  1. If you were sitting at a light in drive (D) with your left foot on the brakes hard and your right foot flooring the accelerator, your transmission would become extremely annoyed with you, not your brakes. This is what Rory is describing and, while it's not strictly what you're asking, I'll second his advice: don't do that.

  2. If you just quickly decelerated from high speed (as in, you were going too fast and stopped very quickly), your brake discs will be quite hot. As you can see from Larry's picture, most of the disc will be able to radiate heat. However, the area that is tightly gripped by the pad (since you're preventing the engine from carrying you forward) is effectively enclosed in a suffocating glove of brake pad. This can leave a residue in that spot and will eventally lead to annoying vibration under braking. In this situation (which I try to avoid), I would be tempted to put the car in park, not neutral.

Like the others have said, neutral is almost never used. It does provide a modicum of comfort, though, to know that reverse and drive aren't immediately adjacent in your gear selection....

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Neutral is there for special cases, such as if/when the car needs to be pulled up onto a flatbed for towing. Other than cases like that, you can just pretend that the "N" notch doesn't even exist. :-)

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The brakes on your car are designed to stop and hold your car whether it is automatic transmission or manual, under what is considered normal driving circumstances. In response to the comment about neutral for towing your car, putting an automatic transmission in neutral and towing for long distance will tear up the tranny. 20 miles or less you should be okay. If all four wheels are on the ground, the drive shaft turning is also turning gears in the transmission. The gears are meant to have the pump in the transmission moving the fluid around to keep everything lubricated and cool. Without the pump working, the fluid will get to hot and cause damage to the integral parts.

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It's not a problem to leave the car in drive; I'd call it more a matter of personal preference.

While the car is idling in D and stopped, the automatic transmission is sort of in a 'ready-and-waiting' mode, with the torque converter partially engaged. This puts a little bit of drag on the engine, and requires the engine management system to deliver a little more fuel and air to keep the idle speed constant. This excess energy is discarded by the transmission as waste heat.

Certain vehicles exhibit more of this than others, but you may actually experience better fuel economy if you let the car idle in neutral instead of drive when stopped for longish periods of time.

I've definitely driven in thick traffic where I was stopped for minutes at a time, and found it far more comfortable to bump the transmission into neutral when the rate of progress was particularly bleak.

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Thanks. I will try this. –  Piyush Kansal Feb 11 at 20:15

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