Out Of Gear - Corolland: the Toyota Corolla Forums

sometimes, while parked at a light or railroad crossing for an extended period of time my friend will shift his auto into neutral because he believes that by taking it out of gear he is saving gas and/or, to a lesser extent, engine and tranny wear. sometimes, after a long and hard stop i will also put her into neutral and keep my foot off the brakes (while stopped) in order to keep from pressing the pads and shoes onto the rotors/drums and leaving burnt pad prints. safety concerns aside, what are the concequences of said actions? all input welcome on additional matters, also. thanks

Depends on what car it is and what type of driving/conditions your will be subjecting the tranny to.

At normal traffic lights, light traffic - I wouldn't even bother to take it out of DRIVE - putting it neutral will not save any gas or wear in normal driving. On some cars (towing, high stall converter) - putting it in neutral will reduce tranny fluid temps, and negligible engine wear advantage.

If you are going to be stopped for an extended period of time - then it would be OK to in PARK, or neutral with e-brake on.

Most driving schools don't recommend shifting to neutral - just in case you need to move in a hurry or start rolling back - you may accidentally perform a "neutral slam" - not real healthy for the tranny.

There is nothing wrong with putting the car in neutral - unless you perform the said "neutral slam" - but for fuel economy gains or wear reduction, not really going to help you. That is why it is an automatic.

Good Luck.

I shift into neutral (sometimes) at red lights as well, because I figure I'm saving some wear, although I have no evidence. Seems like unmeshing the gears would eliminate pressure on the teeth, considering the car creeps forward when in idle if the brakes are not applied. Logic seems to dictate there is some benefit of reducing wear, whether that benefit can be measured or detected is debatable I suppose.

Constant shifting in and out of gear is very abusive on an auto trans.

Ghost: I don't think there's any such thing as unmeshing of the gears in an automatic tranny. From what I know the gears are always engaged. Try this place for some basic (understandable) info: http://auto.howstuffworks.com/automatic-transmission.htm

Automatic and manual transmissions are very different beasts. Based on the info in there, I'd say putting it into neutral is actually harmful as it requires the clutches to be disengaged and then later engaged again. Also, since the torque converter is a viscous coupling, wear should be insignificant with the engine at idle. You might save a tiny amount of fuel... but only if you're stopped for a long while IMO.

Ghost: I don't think there's any such thing as unmeshing of the gears in an automatic tranny. From what I know the gears are always engaged. Try this place for some basic (understandable) info: http://auto.howstuffworks.com/automatic-transmission.htm
Automatic and manual transmissions are very different beasts. Based on the info in there, I'd say putting it into neutral is actually harmful as it requires the clutches to be disengaged and then later engaged again. Also, since the torque converter is a viscous coupling, wear should be insignificant with the engine at idle. You might save a tiny amount of fuel... but only if you're stopped for a long while IMO.

Ok well, something's got to be uncoupled somehow. Otherwise the engine vibrations felt through the body wouldn't cease when you shift into neutral. And the car would still creep forward when idling in neutral.

I looked at the link but my brain is so fried from lack of sleep at the moment my reading comprehension skill is severely impaired. I didn't see any evidence to indicate to the contrary of what I suggested in my first post.

*EDIT*> OK I guess "unmeshing the gears" was perhaps not the correct terminology. And I guess we agree that there is some engagement/disengagement going on, so I guess I see your point about wear involved.

In an automatic transmission, the gears are always "meshed" and all gears are turning whenever the car is moving. What is happening during shifts is that certain groups of gears are linked to the input/output shafts of the transmission through clutches and engagement bands. When you shift to neutral, you are reducing the pressure applied to these clutches and bands, and therefore, upon shifting back into "Drive," you are re-establishing this pressure. This is not a particularly high-wear scenario for an AT; the machine is designed to do it. I occasionally shift to Neutral in situations when I must make a shorter than expected stop due to a sudden traffic light change. Since I am disconnecting the drivetrain from the front-drive axles, stopping distance is greatly reduced. As long as you are fully stopped before shifting from Neutral back to Drive, there should not be any more wear on the transmission than you would normally get by shifting into gear from a stop.

BTW, in a manual transmission, the gears are always meshed together as well. When you shift, all you are doing is connecting engagement devices called "dogs" to the gear you've selected, which causes that gear to be connected to the transmission's output shaft. The engagement "dogs" are brought up (or down) to the gear's speed of rotation by devices called synchronizers which make friction contact with the drive gear and get the "dog" spinning at it's same speed so that the teeth on the dog line up with the matching index slots on the gear. Therefore, you never "grind" a gear; all you are "grinding" is your dog ears when you try to shift before the synchronizers had a chace to work. This is a common mistake made by Boy/Girl racers and others unfamiliar with proper driving practices.