Shifting automatic transmissions to neutral at red light


#1

I shift my auto trans to neutral when approaching a red light. My theory is it reduces brake wear, reduces tranny and motor wear while sitting at the light and uses less fuel to remain in neutral until the light changes. My wife thinks it may harm the tranny. What do you think?


#2

No, it shouldn’t harm the tranny. With modern fuel injection, I don’t think the fuel reduction would be measurable since idle is controlled and the FI cuts the fuel when the throttle is closed. Auto transmissions have over-running clutches which allow the car to roll faster than the engine speed would allow. This was done to save gas making auto trannies closer to manuals. That is why there is essentially no engine braking in high gear. This would negate the brake wear issue. The heat? Yeah should reduce heat a bit.


#3

It won’t harm anything, but it won’t help anything either. Might be just as well to do as the wife prefers when she’s in the car. If mama’s unhappy, EVERYONE’s unhappy!


#4

Just an excercise in futility.
If you had two identical cars and drove one your way and one her way …
in 100k miles you could not calculate a definitive difference in the mpg or brake wear with so many other variables in play when driving.

The worst potential problems with always putting it in neatral…
1 - The huge potentail to forget and have the engine too far revved when you slam it in gear to get going. causing transmission damage that would have never occurred otherwise.
2 - The delay you cause the traffic behind you. ( Yes, car number eight should have made it through that green )
3 - additional wear on shift components.


#5

The last few feet rolling up to a stop light or stop sign, the motor is pulling the car forward. It seems to me the application of brakes then puts brakes countering against motor which means additional brake wear and loss of fuel economy. Seems to me that Idling in Drive drags the motor down (slightly) which would mean loss of fuel economy. Granted, over the course of 80 years of driving this would translate to a meager savings of only $9.99 US. However, invested in mutuals at an annual return rate of 23.69% over the course of the 80 years translates to about a $12,789.24 return on my braking investment. I need the money. Thanks for your responses.


#6

as long as the engine is providing some drag (engine braking), the fuel is cut off at the injectors. Putting it in neutral at this point is actually using more gas. If you slip it into neutral just before you stop (a few feet before complete stop) you may save some gas if you do a lot of city driving and the lights stay red for a long time, but otherwise I doubt you will see a measurable difference.

It won’t hurt the transmission itself but it does add wear to the transmission linkage. I don’t know if it would be enough to cause a repair in the vehicles lifetime because I don’t know anyone that does this.


#7

Now you know somebody, Keith. I’ll report back to you in about 50 years on the impact on my portfolio. Thanks for your response.


#8

More likely to cause problems than save one penny.


#9

While you’re at it, maybe you could apply for a government grant to study this.


#10

In older threads…in this forum…we have beat this horse.

In fact I truly wish my 06 Escape hybrid and 08 Expedition did NOT have a console shifter at all…I could use the extra seat belt there. With a bench seat, the Expedition EL could seat 9.


#11

Every time you shift the car from neutral to drive you are banging on the drivetrain as it goes into gear. I’d prefer extra wear on cheap brake pads than axles and CV joints plus the aggravation of someone constantly shifting. Not as bad as the old days with rear wheel drive and universal joints but still I’d just leave it in gear like everybody else.


#12

Bing, that banging is the only drawback I see to my theory and indeed you may be right that the wear and tear of re-engaging the transmission overrides any brake or fuel savings. Of course, aggravating my wife a bit is worth something as well. Thanks for your response.


#13
. My theory is it reduces brake wear, reduces tranny and motor wear while sitting at the light and uses less fuel to remain in neutral until the light changes. My wife thinks it may harm the tranny. What do you think?

As others said…it won’t help a thing. And I have no idea how you could possibly think it’ll reduce brake wear.


#14

New Hampshire Mike, the last few feet before your car stops, the motor is pulling the car forward, and thus more brake application is needed to stop the car. Hence added brake wear.


#15

Would you not agree that if you timed it perfectly and shifted to neutral so that you rolled up to a stop without ever applying your brakes, you most certainly would reduce brake wear.


#16
New Hampshire Mike, the last few feet before your car stops, the motor is pulling the car forward, and thus more brake application is needed to stop the car. Hence added brake wear.

HUH??? How is the car being PULLED forward? The car is in neutral because the automatic shifted it to neutral or you put the clutch in (for a manual).

Would you not agree that if you timed it perfectly and shifted to neutral so that you rolled up to a stop without ever applying your brakes, you most certainly would reduce brake wear.

Sure if you could and if it wasn’t ILLEGAL and stupid…not to mention the people you’ll be p*ssing off behind you for doing it. The second or third time someone in front of me pulled that stunt…I’d laying on my horn.


#17

Upper right hand corner under the red ‘’ new discussion’’ box …
see the box that says ‘‘search car talk community’’ ?
Type in ‘‘neutral’’ and search …
There are many discussions on this subject.


#18

Thanks, Ken Green. I did find some coverage on the topic. New Hampshire Mike, If your automatic transmission shifts itself to neutral, you’ve got some kind of automatic I’m unfamiliar with. Maybe a centrifugal clutch on your go-kart?


#19
. New Hampshire Mike, If your automatic transmission shifts itself to neutral, you've got some kind of automatic I'm unfamiliar with

When you’re running at a high speed then all of a sudden take your foot of the gas and on the brake…the engine is not spinning fast enough it to effect the transmission via the torque converter. In fact a little engine braking is involved…but not as much as a manual. Then when you get to lower speeds where now the engine speed is faster then the transmission - then yes the engine will put a little pull on the tranny…but so little at this point…it can’t even be measured. So as I said…you will NOT prolong the life of the brakes. All you end up doing is breaking the law and p*ssing off all other drivers around you as you coast to a stop.


#20

Randy, the pull that the engine exerts as you stop is not enough that it will make any difference in your brake wear. All you’re doing is making extra work and putting wear on the transmission by shifting from N back into D every time you pull away from a light. If your wife is anything like me, she may just be annoyed by goofy, irrational habits.