[jcl89]

8AT 2015 M235i with 33K miles. Was slowing to a light and accidentally bumped the shifter to neutral around 20mph. Came to a stop, then shifted back to drive.

As I understand, it's not a good idea to coast at speed in neutral - is this particular incident bad for the transmission?

[SlickShift]

Originally Posted by jcl89

8AT 2015 M235i with 33K miles. Was slowing to a light and accidentally bumped the shifter to neutral around 20mph. Came to a stop, then shifted back to drive.

As I understand, it's not a good idea to coast at speed in neutral - is this particular incident bad for the transmission?

She'll live.

[ianp622]

If it was easy enough to shift it just by bumping it, it's not an issue. Coasting to speed in neutral is not bad for your car, it's just not safe because you don't have the ability to change speeds quickly when you need to.

[Maynard]

There is something in the tranny that does not like this for long term - like going to neutral to coast down hills, but even that is more of a wear issue, not a sudden 'money-shift' parts-breaker. Don't think it is anything that would be a problem for such a quick blip. The subtle fear that now it 'sounds different' is probably just your anxiety f'ing with your head (or is that just me that has that reaction when I start wondering if s/t is broken).

[aerostar]

I shift to neutral all the time in my manual, I don't see why doing it in an auto would be bad for your transmission.

[Maynard]

IIRC, it has to do with the fact that in an auto the system is never fully disconnected like it is with a clutch; I think it may raise line pressures in the wrong parts of the system, or cause overheating that can't be properly cooled unless it is engaged? I mainly recall this as one of those 'things you didn't know about, but need to avoid' from long ago. Either way, I can't imagine that a momentary blip would be a problem, or they would plaster warnings allover the manuals.

[B_Rice]

Not a huge deal, just don't do it all the time.

[msej449]

Sports Auto in EcoPRO does this itself if it can. Going downhill at 70mph, if I take my foot of the power, it disengages and drops down to 700rpm and starts to gain momentum from freewheeling. The big upside is that thanks to the fantastic auto box, as soon as I demand power it re-engages smoothly and I'm back at 2200rpm with power on tap.

There are loads of videos explaining why autos are engineered not to go into N at speed and particularly, the problem and negative effects of re-engaging an auto out of N into D at speed.

When I statred using autos a few years ago, I carried-over my manual habit of going into neutral. But I stopped for two reasons: firstly, because modern autos just don't like being thrown into drive from neutral while moving and second, because of a couple of unforseen situations where I suddenly needed power to manoeuvre immediately, but wasted valuable seconds re-engaging.

But as mentioned, my understanding is that the odd occasion you describe wouldn't be an issue - it's if you do it all the time that you can get heavy wear and tear. The ZF gearbox is a terrific piece of engineering - apparently the first mass-produced box that can (a) maintain hydraulic pressure even when off (hence it's happy with auto stop/start) and (b) jump multiple gears in one go (so can go 5->2, say, rather than 5->4->3->2 and vice-versa).

[jcl89]

Ah got it, makes sense. With the ZF, is it OK to rapidly downshift more than 1 gear (say from 7 to 5), or should I wait a moment in between shifts?

[430409M2]

Originally Posted by jcl89

Ah got it, makes sense. With the ZF, is it OK to rapidly downshift more than 1 gear (say from 7 to 5), or should I wait a moment in between shifts?

The system will refuse to shift if its not capable to do so. Therefore I'd venture to argue it's fine to do.

[mblaucoupe135]

hate to hijack the thread, but in a related note will the auto tranny prevent you from revving it too high?

[crabu2]

Originally Posted by mblaucoupe135

hate to hijack the thread, but in a related note will the auto tranny prevent you from revving it too high?

It's more of the car's engine management stopping it.. It'll cut fuel if you hit red line. So it'll keep bounding off red line.

[mblaucoupe135]

Originally Posted by crabu2

It's more of the car's engine management stopping it.. It'll cut fuel if you hit red line. So it'll keep bounding off red line.

ok thanks. so it's programmed to protect itself, which is good. I am also wondering if this same sort of thing would happen if you tried to downshift to a lower gear that would cause an oveerev? would it prevent this from happening too?

[jcl89]

Originally Posted by mblaucoupe135

ok thanks. so it's programmed to protect itself, which is good. I am also wondering if this same sort of thing would happen if you tried to downshift to a lower gear that would cause an oveerev? would it prevent this from happening too?

Yes, I believe so. The ZF8 will not allow you to downshift if it would cause an over-rev.

[mblaucoupe135]

Originally Posted by jcl89

Yes, I believe so. The ZF8 will not allow you to downshift if it would cause an over-rev.

I figured it did, but wasn't positive. this is good thing as it will prevent the dreaded "money shift!"

[pz619]

No need to worry about the money shift in the ZF8. The computer won't allow the gear change.

As for the neutral issue, it's not an issue. The transmission does this automatically in eco pro mode anyways.

[ZPrime]

FWIW, even the DCT on an M car won't allow you to moneyshift, and that is much more like a manual than the ZF8 (it doesn't creep from a stop until you give it gas, for example).

[Gabrola]

Originally Posted by pz619

No need to worry about the money shift in the ZF8. The computer won't allow the gear change.

As for the neutral issue, it's not an issue. The transmission does this automatically in eco pro mode anyways.

I'm surprised this thread went on this long before anyone mentioned that car is already designed to do this.

[harma24]

Originally Posted by Gabrola

I'm surprised this thread went on this long before anyone mentioned that car is already designed to do this.

Sort of, yes. It will do this in EcoPro mode. But the owners manual specifically recommends against coasting in neutral. I believe the reason behind that recommendation is because the car will re-charge the battery while coasting. However, it does not do that if it's in neutral. If the battery cannot recharge while coasting, it will need to recharge while driving, which impacts fuel economy.

[pz619]

Originally Posted by harma24

Sort of, yes. It will do this in EcoPro mode. But the owners manual specifically recommends against coasting in neutral. I believe the reason behind that recommendation is because the car will re-charge the battery while coasting. However, it does not do that if it's in neutral. If the battery cannot recharge while coasting, it will need to recharge while driving, which impacts fuel economy.

Same with eco pro mode using coasting. I think the reason it's in the manual is more because of safety. You need to apply the brakes I think to put it in gear from neutral, which wouldn't be the safest thing if you are moving but want to get into gear to accelerate.

[ZPrime]

N -> D shouldn't require the brakes (doesn't on most autos at least)... N -> R should though.

[pz619]

Originally Posted by ZPrime

N -> D shouldn't require the brakes (doesn't on most autos at least)... N -> R should though.

I think it does in the 2er. I'm not positive but I'm willing to do a parking lot test later this afternoon. I feel like I've seen the message before but I'm not positive now that you bring it up.