Auto transmission - Page 3 - BMW 3-Series (E90 E92) Forum

ss134 · 04-25-2012, 05:05 PM

Quote:

Originally Posted by BIGTIME

Get yourself an M3. You won't have to worry as they have auto stop start

. However, mine doesn't always stop start.

It will only stop/start in D mode and wont do it with AC on or when the outside temp drops to a certain level. There are a few other instances when it won't come on either....i just turn mine off anyway!

With regards to the auto transmission - one of the things i like so much about DCT is that the car does not 'creep' when you take your foot off the brake like a standard auto which means you can hold the car on the brakes at the lights like a manual without the engine taking any strain (even though it is minimal)

BIGTIME · 04-25-2012, 05:14 PM

I usually turn mine off. I thought it was something to do with the climate control. I leave my air con on all the time as it supposedly stops bad odours in the car and the auto ss does still kick in sometimes.

mjh93sa · 04-25-2012, 05:45 PM

It's an often disputed subject and on the whole I think that everyone is right... and talking bollocks.

If you leave the 'box in drive then you are applying power to the drivetrain. This must be overcome by either the foot brake or the handbrake. BMW handbrakes are not the best, but can certainly hold against the creep of a modern 'box (my 135i certainly could and i would use it for a stop of say a single traffic light cycle to avoid blinding the guy behind).

Additionally, with the drive all hooked up the torque converter is doing work to apply power, so given the usual frictional losses etc it will be heated by this action and without motion there will be less cooling airflow. But it's in the most lightly loaded state and for a short period of time, certainly no worse than creeping through dense traffic chewing on the exhaust gases of the car in front with little cooling airflow. The granny in the Fiesta next to you doing 3k revs and using the clutch for speed control is going to have problems, not you.

Shifting into neutral will casue wear by engaging and disengaging drive, selectors are moving, gears are engaging, etc, etc. But, properly designed and manufactured all of these moving parts can do so over and over again for one hell of a long time.

A quick example. The gear teeth within a gearbox are subject to all sort of loads. As they mesh and disengage each gear flank is rubbing over it's counterpart in the mesh. It is then subject to the absolute forces being transmitted through it as well as the effects of cyclic loading (fatigue). However, with the correct material selection, surface hardening and general design they can be expected to last the life of the car. Just think how many times those parts are engaging and disengaging. It doesn't mean of course that they do design for infinite life in a car (BS ISO 6336 is a riveting read if you want to start to look at gear design

).

So, back on topic, and in short. Yes all methods have their advantages and drawbacks, but with modern designs you shouldn't have a problem with either method.

Personally my preference in the 135i was to use the footbrake for short stops, the handbrake (with a foot hovering over the brake) for slightly longer stops, and only shift to neutral if it was clear that you would be stopped for some time.

mick_n3 · 04-26-2012, 02:22 AM

Bit of a hijack Sorry OP
What's the opinions on changing auto box oil, BMW say it's seal for life but I'm sceptical, I know there is no drain plug but I see GSF and a couple of other suppliers are doing a filter and sump pan assembley. Is it worth doing it, sealed for life mmmm how long is life when i breaks?

04-25-2012, 05:45 PM	#47
mjh93sa Major General Drives: M135i Join Date: Dec 2005 Location: Gloucestershire Posts: 5,075 iTrader: (0) Garage List 2012 BMW M135i [5.00] 2011 Mini Countryma ... [2.75]	It's an often disputed subject and on the whole I think that everyone is right... and talking bollocks. If you leave the 'box in drive then you are applying power to the drivetrain. This must be overcome by either the foot brake or the handbrake. BMW handbrakes are not the best, but can certainly hold against the creep of a modern 'box (my 135i certainly could and i would use it for a stop of say a single traffic light cycle to avoid blinding the guy behind). Additionally, with the drive all hooked up the torque converter is doing work to apply power, so given the usual frictional losses etc it will be heated by this action and without motion there will be less cooling airflow. But it's in the most lightly loaded state and for a short period of time, certainly no worse than creeping through dense traffic chewing on the exhaust gases of the car in front with little cooling airflow. The granny in the Fiesta next to you doing 3k revs and using the clutch for speed control is going to have problems, not you. Shifting into neutral will casue wear by engaging and disengaging drive, selectors are moving, gears are engaging, etc, etc. But, properly designed and manufactured all of these moving parts can do so over and over again for one hell of a long time. A quick example. The gear teeth within a gearbox are subject to all sort of loads. As they mesh and disengage each gear flank is rubbing over it's counterpart in the mesh. It is then subject to the absolute forces being transmitted through it as well as the effects of cyclic loading (fatigue). However, with the correct material selection, surface hardening and general design they can be expected to last the life of the car. Just think how many times those parts are engaging and disengaging. It doesn't mean of course that they do design for infinite life in a car (BS ISO 6336 is a riveting read if you want to start to look at gear design ). So, back on topic, and in short. Yes all methods have their advantages and drawbacks, but with modern designs you shouldn't have a problem with either method. Personally my preference in the 135i was to use the footbrake for short stops, the handbrake (with a foot hovering over the brake) for slightly longer stops, and only shift to neutral if it was clear that you would be stopped for some time. __________________ Gone: Fiesta - Focus - E46 320dSE - E91 330dMSport - E82 135iMSport - R55 JCW Clubman Now: M135i with lots of toys

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04-25-2012, 05:14 PM	#46
BIGTIME Lieutenant Drives: E92 M3 DCT - Mineral White Join Date: Mar 2010 Location: North East Posts: 494 iTrader: (0)	I usually turn mine off. I thought it was something to do with the climate control. I leave my air con on all the time as it supposedly stops bad odours in the car and the auto ss does still kick in sometimes.

04-26-2012, 02:22 AM	#48
mick_n3 New Member Drives: e90 320d Join Date: May 2008 Location: Kettering, U.K Posts: 25 iTrader: (0)	Bit of a hijack Sorry OP What's the opinions on changing auto box oil, BMW say it's seal for life but I'm sceptical, I know there is no drain plug but I see GSF and a couple of other suppliers are doing a filter and sump pan assembley. Is it worth doing it, sealed for life mmmm how long is life when i breaks?