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This is not with the intention of saving fuel (as I have seen many answers assuming savings in fuel while doing this). But I have this habit of putting the vehicle into neutral before approaching stops (red lights). The main reason behind doing this being, is to reduce the strain of holding the brake pedal.

One of my friends is arguing that it's not good for the transmission system, shifting the transmission from D to N while the vehicle (with automatic transmission) is moving. I couldn't agree with him, as I couldn't find any issues with this. Also I couldn't find any information regarding the same on the manual for Toyota Corolla.

Do you guys have any technical details about this?
Thank you in Advance.

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I believe WRT manual transmissions, the idea was to reduce wear on the clutch and use the brakes instead, which are far easier to replace. –  Drise Jul 11 '12 at 0:34

4 Answers 4

up vote 6 down vote accepted

Being in Neutral or Drive should have negligible to no effect on the distance the vehicle travels when the accelerator is not pressed because the torque converter disengages the engine below predetermined RPM levels.

However, if you somehow were to push just a little too hard and sent the transmission into Reverse instead of stopping in Neutral, you would most likely be faced with purchasing a new transmission.

Update:

Rafi: If, by your question, you mean to say that you put the transmission into Neutral while waiting at a stop light, then this would not harm the transmission in any way.

Though it will not harm your transmission to shift into Neutral while your vehicle is in motion, the additional wear on your brakes by leaving the transmission in Drive will be negligible over the life of the brake pads. It is that minor.

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WRT "reverse", this isn't true on modern cars. Mythbusters did exactly this and showed that putting the selector in reverse put the transmission in neutral to no net effect. dsc.discovery.com/fansites/mythbusters/db/transportation/… –  Bob Cross Jul 10 '12 at 18:47
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Unless automatic transmissions have changed recently, and being in D definitely changes the amount of motion when you take your foot off the brake while the car is at rest. I'm a little interested to know how you've experienced anything else! –  Colin K Jul 11 '12 at 17:05
    
Isn't it also true that in most modern cars, you are unable to accidentally push the shifter into reverse without pressing some sort of unlock button, as you would to take the car out of park. –  0x7fffffff Jul 15 '12 at 10:47
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Colin, my information is in reference to a vehicle moving at speed. You are talking about a stopped vehicle. These are different states for the torque converter. –  jp2code Jul 15 '12 at 12:21

NEVER, EVER go into neutral while slowing down to a stop, for 3 reasons: 1. You lose the added benefit of engine braking if the car's not in gear 2. If you have to quickly avoid something by accelerating and moving out of the way, you'll hit the gas and won't go anywhere 3. If the light turns green before you come to a complete stop, you'd have to go back into drive while moving. And you should only go into drive when stopped, really, really bad things may happen to your transmission if you shift to drive while moving.

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your first two points are perfectly valid, but why do you say that "really really bad things may happen" if you shift into drive while moving? –  vlsd Apr 11 at 21:46

I do this quite a bit, actually, and I don't think there's any difference in shifting from drive to neutral when the car is moving or stopped. The reason is that the torque converter is hydraulic, so it gives you transmission some slack in order to let it shift, just as if you were pushing on a clutch. The shifting cannot possibly put more wear on the trasmission that the transmission shifting between 2 and 3, for example, something that it does thousands of time in one year. In fact, going into neutral probably puts significantly less wear on the parts than that, since you're going from a configuration where gears are engaged into a configuration where they are not.

P.S. The reason I shift into neutral at stop lights is that my car vibrates quite painfully when in drive and stopped. I haven't been able to figure that out yet, but that's another post.

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No, Not at all. Someone said here this:

"You lose the added benefit of engine braking if the car's not in gear"

Not true for automatic gears. Transmission still will allow the power from engine to go to wheels. Putting in Neutral will cut the power immediately and shorten the distance you need to come to a full stop. Try stopping from 40 mph with and without putting in neutral. You will even feel the car slowing down a lot faster in neutral.

This might be very helpful if you are speeding on highway and need to stop as short as possible, or in fully stopped/stopping for traffic like red a light.

I doubt putting in Drive harms the transmission because at all. in fact it might be less harmful than putting in Drive when fully stopped because car will not need all the power to move, because it has already have some speed.

All above ASSUMING that you will not put the pedal to the medal (accelerating in Neutral). Shifting to Drive at high RPM is very harmful to the transmission, let alone high RPM may cause problem for the engine as well in the long term.

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This really is bad advice all the way around. Automatics still engine brake. Shifting out of drive and into neutral every time you need to stop creates wear and tear on the transmission and valve body. The drive train already has a device which will allow it to decouple the engine from the transmission ... it's called a torque converter. It will stay engaged as long as the engine is above a certain RPM, then will decouple when it gets below it, doing what you are suggesting without the need for the wear and tear from shifting. –  Paulster2 yesterday

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