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how does one (properly) drive an automatic

Posted by jaffar 
Please bear with me smiling smiley

What is the proper way to drive an automatic ? While cruising it seems obvious, just D it and forget. But what about city traffic, when I have to stop every few meters, then I have to wait 1-2 minutes at the red light etc ? Do I just keep it in D all the time, or do I shift to N ?

The car owners manual is not specific about this.

Thanks

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A physics truck just turned over outside. There's physics everywhere!



Edited 1 time(s). Last edit at 05/22/2013 06:04AM by jaffar.
The automatic transmission is designed to be left in gear...that is the whole point of the torque converter.
Putting the car in neutral may save a little fuel but it isn't going to make much difference as far as wear goes.
Interesting. Never had an automatic myself...
Is the tear and wear of shifting to N and D every traffic ligh significant? Are there any savings in doing so?
Most people I know who drive automatics (and I know few) just drop D and accelerate or brake.
At red-lights I'd certainly put it in N. No need for the extra load on the engine, wanted to creep but being held by the brakes.
Peter is correct -- automatic transmissions are designed to be left in gear. Any load placed on the engine by idling in Drive is trivial to the point of insignificance. The wear placed on the shift linkage from shifting back and forth is probably higher (but also insignificant).

Here in the U.S., where automatics are the rule rather than the exception, what drives me most crazy is people who don't know how to drive an automatic down hills. I live in a mountainous region, and I frequently see drivers riding their brakes down miles of mountain roads instead of shifting into a lower gear. It's like they're afraid their engine will blow up if it goes over 2500 RPM. I once saw a van at the bottom of a mountain road with its brakes literally on fire because the driver had kept it in "D" all the way down the mountain.

__________
Dave
'91 325iX
What I meant was that it's pointless to keep it in D, using a lot more fuel than needed to be standing still. Best solution would still be to turn the engine off at longer pauses.
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Michiel 318iS
What I meant was that it's pointless to keep it in D, using a lot more fuel than needed to be standing still. Best solution would still be to turn the engine off at longer pauses.

Define "longer pauses".
I can't believe the feature "start-stop" in new cars is that much a worthy thing, cause the increased stress on the starter motor and bigger battery offsets the small benefit to be gained in turn off the engine for less than one minute. But I have never read any decent study on that, so... :whistle:

Îf the distance to be covered is small, best thing is to walk.
Imagine all the exhaust gasses in a city being emitted by just sitting in front of a red light, engines running for nothing. It won't make a large difference in your fuel consumption, but all tiny bits counted together, it makes an awful lot as a grand. As long as your battery is able to recover afterwards, it makes sense turning off the engine for any stop longer than 30 seconds. I don't do it at every traffic light, but the ones where I know I have to wait for a while and where I can predict some way when it will turn green, I turn the engine off.
As a 1992 325i convertible 4 speed automatic driver, stop and go is handled OK by D. But the 325i is a long stroke- high rev engine, so when acceleration is my goal like a freeway on ramp then I shift through the gears. This allows all of the newer cars to appreciate the old man's long power band and smooth shifting.
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rvgammill
As a 1992 325i convertible 4 speed automatic driver, stop and go is handled OK by D. But the 325i is a long stroke- high rev engine, so when acceleration is my goal like a freeway on ramp then I shift through the gears. This allows all of the newer cars to appreciate the old man's long power band and smooth shifting.

Does your step down not work properly? I never had a problem with rapid acceleration when simply planting the accelerator peadl to the floor; which immediately transformed the iX into a rocket, surprizing many winking smiley

Also, the 325i is not a long stroke emgine. The 2.7 eta is the stroker which although producing less hp does pump out significantly more torque.
Generally, long stroke engines are low revvers, as the piston speed would go up way too high.



Edited 1 time(s). Last edit at 12/14/2013 02:42AM by Michiel 318iS.
Hello everyone

Last night I did something that I haven't done in years. In local language it's called approximately "stupid man's breakdown" - I drove until I had no more fuel sad smiley
Since I was very close to a gas station, I did not stress, thinking I would be able to push the car for 300 meters with no problems, especially since the road was a bit downhill. I smiled remembering the E30 (manual gearbox) days, when I could push it with one finger or, on windy days, I could just coast for a few kilometers.

Well, apparently it's not like that. I've pushed my Z4 auto in the garage a few times, but only for a few meters. Now I found out that it's VERY hard to push it, even downhill. It's doable, but as soon as I stop pushing, it stops, like someone's braking.

I know the user manual says not to tow an automatic tranny unless the driving wheels are suspended, but I would very much like to understand why and what the hell is going on in there. Why have the N(eutral) position at all ? Clearly the driving wheels are still linked to a part of the transmission, making it impossible to push. I wonder how fast the car will stop by itself if I select N while driving...

Thanks


           _
          {_}
          / \
         /   \
        /_____\
      {`_______`}
       // . . \\
      (/(__7__)\)
      |'-' = `-'|
      |         |
      /\       /\
     /  '.   .'  \
    /_/   `"`   \_\
   {__}###[_]###{__}
   (_/\_________/\_)
       |___|___|
        |--|--|
       (__)`(__)

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A physics truck just turned over outside. There's physics everywhere!
Correction about towing, from the user manual:

Automatic transmission
Selector lever in position N.
Do not exceed a towing speed of 45 mph/
70 km/h or a towing distance of 90 miles/
150 km. Otherwise, the automatic transmission
could be damaged.

So... why the hell won't it go downhill or allow me to push it ? sad smiley

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A physics truck just turned over outside. There's physics everywhere!
I know nothing about the automatic internals, my advice is to walk to the gas station and bring back a can of gas, instead of pushing the whole car.
:wavey:

yahoo
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Jose Pinto
I know nothing about the automatic internals, my advice is to walk to the gas station and bring back a can of gas, instead of pushing the whole car.
:wavey:

yahoo

Indeed, that is the normal procedure. I am also not familiar with automatic transmissions, but even cars with manual gearboxes can be hard to push, particularly if the brakes are slightly stuck on.


Apparently the automatic transmission never disengages from the transmission, unlike manual transmission when in neutral. Manual transmission output shaft spins freely, when in neutral.
So the automatic, even in N, have the internal parts working as the car was being driven, which causes friction, and holds back the car when it's towed.
The problem is that when you stall the engine and then put it to N, you aren't very sure what state the transmission is in: which clutch and what brake is free and/or (partially)engaged, which could cause some extra friction. After a while, pressure could drop in the valves and pistons, freeing up the brakes and clutches, but that might require more time than to overcome 300 m by walking.
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Jose Pinto
... unlike manual transmission when in neutral. Manual transmission output shaft spins freely, when in neutral.

Automatic transmissions are a mystery to me. I've never owned one and hopefully never will.

But I do know why one should not tow a car in neutral with a manual transmission for any great distance. See image below.

The green shaft and gear is the input from the engine. When the clutch is engaged (pedal up) and the engine is running, that green gear turns with the engine.

That drives the red shaft and all the gears in the bottom of the transmission, the layshaft or countershaft. It's all one solid piece.

The blue gears are constantly meshed with their corresponding red counterparts and thus always spin with the red gears when driven by the green input gear.

The blue gears spin freely, all at different speeds, as they ride loose on the yellow output shaft.

The purple dog collars (shown without synchromesh mechanisms) are splined onto the yellow output shaft. They slide forward or back along the yellow output shaft when the gear selector is moved to lock any particular single blue gear to the output shaft.

If the car is towed in neutral without the engine running, it means the green shaft is not turning. Hence the red shaft and all its gears are also not turning, and all the blue gears are also stationary. However, the yellow output shaft is connected to the rear wheels thru the differential and thus the output shaft will spin at road speed.

The problem with that is, without the engine running and thus not driving the red countershaft, the oil just sits in the bottom of the transmission case instead of being thrown up by the countershaft. That means the yellow output shaft is spinning inside each of those blue gears without the benefit of lubricating oil.

If you do that long enough and/or fast enough you'll ruin the output shaft and its bearings.


I agree, Ferdinand. But the drawing of the gearbox had me a bit confused. Isn't there usually a direct gear, where the green and yellow shaft are connected with no gears?

So for towing longer distances, should we put the transmission in second gear, and ride the clutch instead? Or maybe at least some of the time?
There is always some gear, when the ratio is 1, they have same dimension, number of teeth.

Is a common practice to tow manual cars with wheels rolling, in neutral, with not much damage apparently.
A manual gear box can actually run without oil in it for a while, before failure. and even so, the failure may be in just one gear and possible to be repaired by a skilled mechanic.
The automatics seem to be more vulnerable.
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Ove Kvam

So for towing longer distances, should we put the transmission in second gear, and ride the clutch instead? Or maybe at least some of the time?

For long distance towing of a manual transmission, either lift the drive wheels and let it roll on the non-drive wheels, or in the case of our front engine / rear drive cars, you can unbolt the driveshaft from the differential or remove it completely. Actually, the best way to tow any car is probably to just put it on a flatbed and not take any chances with more damage.

John
Depends on the gearbox design. Longitudonal positioned transmissions often have a direct gear, transversal ones have to be as short as possible, in recent years a lot of them have become multishaft without a direct gear.
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