May 22, 2013 04:04AM
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Registered: 15 years ago
Posts: 187 : Bucharest, Romania |
Please bear with me
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 -- A physics truck just turned over outside. There's physics everywhere! Edited 1 time(s). Last edit at 05/22/2013 04:04AM by jaffar. |
May 22, 2013 08:50AM
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Registered: 15 years ago
Posts: 1,538 |
May 22, 2013 10:21AM
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Registered: 14 years ago
Posts: 799 : O Porto |
May 22, 2013 12:27PM
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Registered: 15 years ago
Posts: 670 |
May 22, 2013 01:50PM
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Admin
Registered: 15 years ago
Posts: 584 : Vermont, USA |
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 |
May 23, 2013 12:10PM
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Registered: 15 years ago
Posts: 670 |
May 24, 2013 03:24AM
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Registered: 14 years ago
Posts: 799 : O Porto |
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... Îf the distance to be covered is small, best thing is to walk. |
May 24, 2013 12:49PM
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Registered: 15 years ago
Posts: 670 |
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.
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December 11, 2013 08:29AM
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Registered: 10 years ago
Posts: 8 |
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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December 12, 2013 10:22AM
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Registered: 15 years ago
Posts: 1,538 |
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 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. |
December 14, 2013 12:42AM
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Registered: 15 years ago
Posts: 670 |
December 24, 2015 03:03AM
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Registered: 15 years ago
Posts: 187 : Bucharest, Romania |
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 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__)\) |'-' = `-'| | | /\ /\ / '. .' \ /_/ `"` \_\ {__}###[_]###{__} (_/\_________/\_) |___|___| |--|--| (__)`(__) -- A physics truck just turned over outside. There's physics everywhere! |
December 24, 2015 03:46AM
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Registered: 15 years ago
Posts: 187 : Bucharest, Romania |
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 ? -- A physics truck just turned over outside. There's physics everywhere! |
December 25, 2015 03:26PM
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Registered: 14 years ago
Posts: 799 : O Porto |
December 26, 2015 12:34AM
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Registered: 9 years ago
Posts: 136 |
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. |
December 26, 2015 08:39AM
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Registered: 14 years ago
Posts: 799 : O Porto |
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. |
January 08, 2016 02:55PM
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Registered: 15 years ago
Posts: 670 |
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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January 20, 2016 05:55PM
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Registered: 15 years ago
Posts: 797 : Ottawa |
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. |
January 20, 2016 11:04PM
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Registered: 9 years ago
Posts: 136 |
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? |
January 21, 2016 04:14PM
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Registered: 14 years ago
Posts: 799 : O Porto |
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. |
February 04, 2016 04:36PM
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Registered: 15 years ago
Posts: 202 : Knoxville, TN |
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 |
March 06, 2016 03:31PM
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Registered: 15 years ago
Posts: 670 |