Driving Style and Autobox Wear

[kevinororke]

Hi,

"Arnie's Answers" in the May 2007 Mercedes Owners mag gives what I think is incomplete advice about driving with an autobox. However, my question is not about that very complex subject. Among other things Arnie suggests that leaving the box in D rather than shifting to N when stationary causes less wear. I leave the transmission in D most of the time. However, there are times when moving to N is the only safe thing to do. Eg when waiting to join a busy 60 mph main road at a junction. If the main road traffic is moving fast I apply the parking brake and knock the transmission into N. An accidental creep (or shunt) forward would be catastophic. I also hover my foot over the service brake. There are other examples. The question is mechanically why does it cause more wear to select N too frequently ??

Regards, Kevin

 

[BlackC55]

I am a little worried that you would let the car creep while in D. Do you not have control of your leg on the brake pedal?

Maybe you should not drive at all if you do not........

 

[Hibbo]

Yes.

Every time you move from N to D causes wear.

When stationary in D the gear stays engaged and everything in the box is still.

 

[television]

I have never moved the auto gear shift in D on any car whilst driving autos since 1960

 

[kevinororke]

Hi,

I don't let my car creep at potentially dangerous junctions, but if the box is in D, the parking brake is off and your foot slips off the service brake (say caused by a rear shunt) you could creep a few feet into the opposing traffic stream. Anyhoo ! Anybody got any more detail about why shifting to neutral causes wear ? Do you get the same wear shifting between gears ?

Kevin

 

[television]

Hi,

I don't let my car creep at potentially dangerous junctions, but if the box is in D, the parking brake is off and your foot slips off the service brake (say caused by a rear shunt) you could creep a few feet into the opposing traffic stream. Anyhoo ! Anybody got any more detail about why shifting to neutral causes wear ? Do you get the same wear shifting between gears ?

Kevin

Moving out of D is what causes the unnecessary wear. If you are rear shunted either the car that you hit will stop you, or if your just drift out,you have a chance to recompose your self and apply the footbrake

 

[panason1c]

I always select 'neutral' if i know that i have a reasonable time to wait before moving off (ie...traffic lights just gone to red) ..... the transmission is under load when stationary in 'drive' which is exhibited by the 'creep' factor.....i'm not an auto-trans specialist but surely, when stationary, the gearbox is suffering less wear and tear in neutral than it is in 'D' and under load (albeit, a light load)

I'm sure a auto-box specialist can give us the definitive answer!

 

[television]

I always select 'neutral' if i know that i have a reasonable time to wait before moving off (ie...traffic lights just gone to red) ..... the transmission is under load when stationary in 'drive' which is exhibited by the 'creep' factor.....i'm not an auto-trans specialist but surely, when stationary, the gearbox is suffering less wear and tear in neutral than it is in 'D' and under load (albeit, a light load)

I'm sure a auto-box specialist can give us the definitive answer!

This being the case,why do MB fit the" Stop" function to the braking system now to prevent creep if it harms the box.

This has been covered so many times.

 

[Parrot of Doom]

If you get shunted while in D, the car will be limited by the maximum speed of the drivetrain in that gear.

If you get shunted while in N, the car will move forward at something close to whatever speed the vehicle that hit it was doing.

I know which scenario I prefer. Speaking of this, how many people keep their wheels pointing straight ahead while waiting to make a right turn off a busy road? Far too few from my experience.

 

[panason1c]

This being the case,why do MB fit the" Stop" function to the braking system now to prevent creep if it harms the box.

This has been covered so many times.

Probably to stop drivers from 'creeping' into the stationary car in front...

 

[television]

Probably to stop drivers from 'creeping' into the stationary car in front...

well that one reason, the other being so that they can take their foot off the brake and get out if they want to

 

[panason1c]

well that one reason, the other being so that they can take their foot off the brake and get out if they want to

I, for one, would be extremely uneasy about 'getting out' of my very expensive Mercedes whilst relying on 'electronics' to stop it going walkabouts. :-?

 

[whitenemesis]

Hi,

I don't let my car creep at potentially dangerous junctions, but if the box is in D, the parking brake is off and your foot slips off the service brake (say caused by a rear shunt) you could creep a few feet into the opposing traffic stream. Anyhoo ! Anybody got any more detail about why shifting to neutral causes wear ? Do you get the same wear shifting between gears ?

Kevin

It is moving the selector that causes the wear. Leaving it in D causes no more wear than driving along

 

[Mr Teddy Bear]

Why I slip it into Neutral


I've given this some thought.....................
Just for those who dont know a auto box is a number of epycyclic gear
trains mounted on one shafte ( so no mainshaft/layshaft layout )
all covered by a series of groved drums. For gears 1 to top-1 each gear is
engaged by a brake band around the drum which clamps it and stops it from
turning.
Therefore the additional wear when the lever moves from n to d is the action
the band braking either 1st or second gear drum from tickover rev's to zero.

The effect of leaving in D and applying the parking brake is to brake the box
side of the Torque Converter while the engine side rotates at tickover,
this will have two efects;
a) increased engine load uses more fuel
b) increased shear in the TC increases the temp' of the transmission fluid

My car especialy in S mode displays a grat deal of creep.
In my opinion moving from d to n bearing in mind the normal operation of
box means the train is turning at far higher revolutions, the so called increased wear will be negligable.

Happy CLK driver sitting in neutral.

 

[whitenemesis]

Quote from owner's handbook..

Stopping
If you are only stopping briefly and the driver is not getting out of the vehicle:

Leave the selector lever in the drive position.

Prevent the vehicle from rolling away by applying the brakes.

Guess it depends on you definition of "briefly"

 

[230ceBruno]

Well fancing my self as a driver's driver , loving driving (sorry global warming) and having owned manuals until my most recent 2 cars, I have a habit of shifting to 3 before I pull away from lights, etc. How does this wear talk figure in my case?

Can something Like Lucas Oil ATP additive mitigate for the 'damage' I have been doing to the car? :-?

BTW panason1c loved your take on creeping

 

[panason1c]

Done a quick internet search and found plenty of reasons for selecting neutral when stopped but none found for leaving in 'drive'......below is just one example.........i, personally, see no advantages in leaving in 'drive'.

http://auto.howstuffworks.com/how-to-drive-economically6.htm

Saving Gas While Standing Still
Even when your car is standing still, you can be saving gas. Here are some strategies.

Shift to Neutral When Stopped

If you're not moving but your engine is running, you're getting zero miles per gallon. Idling at a traffic light is a fuel-economy killer, as is waiting to clear a construction zone or sitting while a freight train crawls by. And there's a good reason our most frustrating traffic condition is called stop-and-go driving.


Notice that shifting your automatic or manual transmission into neutral calms down your engine note and drops the rpm. That saves gas. Shift into neutral even for a long traffic light.


Keeping an automatic transmission in Drive puts an extra load on it, which drains fuel. In neutral, it's resting -- or at least as close to rest as an automatic ever gets. This shift is even more important when the air conditioner is running, so the engine doesn't have to strain so hard while idling. A manual transmission should be shifted to neutral at every stop.

 

[Parrot of Doom]

Thats a pretty poor example. Saving 'gas' at the expense of wearing down a gearbox is hardly a saving IMO. Its like using the engine and gearbox to slow the car, rather than using the brakes - because after all, you're saving the pads and discs from wear......

 

[panason1c]

Quote from owner's handbook..

Stopping
If you are only stopping briefly and the driver is not getting out of the vehicle:

Leave the selector lever in the drive position.

Prevent the vehicle from rolling away by applying the brakes.

Guess it depends on you definition of "briefly"

I think the above quote from the manufacturers handbook is definitive....and renders the word 'briefly' as academic.....the point being that whether 'briefly' means seconds...or minutes, the instruction is clearly NOT to leave it in drive for any longer than 'a short period' when stationary......they presumably have a reason for this?

I would love to hear the take on this subject from an experienced transmission repair specialist!

 

[jberks]

I can't see the point either.
As far as economy goes, I imagine modern torque converters are relatively low load during idle. This is especially true with the newer ones and why, I suspect, they tend to roll back more than older models. As mercs tend to have big engines, the aircon argument falls flat. They are producing enough power at idle to run it without effort.

I have read comments on neutral/hand brake whilst waiting at a busy road junction so you don't creep into the traffic. Wouldn't that be classed as not having the car under proper control? This neutral and handbrake idea IMO is possibly one of the most dangerous. The car becomes an uncontrollable chunk of metal. Handbrakes are notoriously unreliable and when you are ready to go, you have to shift back into gear and release the handbrake (take control again) before you can do anything.
No - footbrake/SBC hold and in D for me every time. I am confident it isn't going anywhere and can take off in an instant should the need/opportunity arise.

Interestingly, anyone know how clever SBC hold is? Would it tighten the brakes further if one wheel moved or is it pretty much max braking anyway?

Oh - and I have got out whilst in the D/SBCHold - bit worrying but it was just fine.