uchu47

The question that bothers me for a while.... Being old lol, I used to drive manual before and often used neutral on long descends. Later on used N the same way on automatic Toyotas/Nissans with no issues.

However MB manual explicitly states you can't use N while driving because it will damage transmission.

Are there objective reasons transmission can be damaged while running on N? Or Benz is just protecting themselves from people who accidentally put R and mess up the car?

I am well aware of safety implications and sorts - not like sticking N whenever car gets rolling, but sometimes it makes sense to let engine rest at 600rpm and let the car run longer without pushing all transmission.

What are your thoughts?

JettaRed

iTrader: (1)

Follow the manual. You don’t want to risk damaging the tranny to “let it rest”. I suspect the torque converter would be unhappy being over-driven by the driveshaft. Coasting in neutral is inherently dangerous and unnecessary. Plus you do not want to reengage at 60 mph.

Odd Piggy

Damage would not be immediate, and I’m not sure if anyone knows just how much you can get away with.

Different style transmissions may behave differently. Dual Clutch Transmissions (DCTs) are essentially self shifting manual transmissions. The caution usually does not apply to these. Planetary transmissions with overrunning clutches and those with wet plate clutches, Continuously Variable Transmissions (CVTs), Automated Manual Transmissions, and other types depend upon the design as to whether they can be used to coast for long distances in neutral.

JettaRed

iTrader: (1)

But why? What really is to gain? I highly doubt you are extending the life of the transmission more than if you service it as specified. And in some places it is illegal.

https://trafficticketdefenseblog.com...es-part-two22/

BlackML550

At best a marginal fuel saving. False economy. And it essentially negates all the ABS/ESP functions which will switch off if they can't read transmission speed. Makes no sense.

uchu47

So where is the damage coming from?

uchu47

Gentlemen, to make it clear once again I am not discussing legal issues or whether it's a good idea to do or not. Just technical perspective - is it actually damaging anything?

Whether it is "false economy"/dangerous or not everyone can decide for himself after weighting in all factors, we are all grown ups here.

TripleDown

Shifting into neutral and coasting....probably not.

Re-engaging D while the car is moving , different story. I've done this on other cars when I was much younger and some of the clunks from the driveline convinced me to give it up.

Your car, your money....

Odd Piggy

When the engine is running, the hydraulic pump (front pump), which is directly coupled to the torque converter output, is running. Therefore, pressure and lubrication are available. All of the clutch packs and brake packs are open. So mechanically there should be no issue with coasting in neutral with the engine running.

However, MB transmissions are all electronically controlled and an issue could conceivably arise since coasting for a long distance in neutral is not normal operation and the control program may not provide a reasonable output for the situation. This could result in an “implausible” value causing a DTC to be stored and eventually a “service” message to be set. In the worst case, the ECU may even set the transmission to limp home mode. The 722.9 workshop manual does not address coasting in neutral, so only those who have tried will know if this actually occurs.

JettaRed

iTrader: (1)

Let's settle this once and for all. @uchu47 please test this out and report back to us if your transmission survived. However, regardless of your outcome, I don't think I will do it.

On this general subject of "questionable things to try", opening the driver's door while the tranny is in drive will move it to Park. Can you check if this happens only while stopped or will it happen with the car is moving, as well?

Thanks

Odd Piggy

There are a lot of off the deep edge speculations out there about this. I found a UK club site stating that C Class cars could be towed 50 km with all 4 wheels down in neutral with engine running. !!! It suggested NOT USING A ROPE TO DO IT.

Adi-Benz

Yeah this is totally fine and I've done it plenty of times in my car. But of course, you don't want to throw it back into 1st/2nd gear at an obnoxiously high rpm.

The wheel speed sensors still read and no implausible values are generated.

Prefacelift does not throw into park when opening door in reverse. Unless the facelift models do so, generally this is for the vehicles with the stalk gear selector.

JettaRed

iTrader: (1)

You're right. The mechanical shifter in my 2014 C350 does not physically move to Park when opening the driver's door. However, my 2015 SL400 with an electromechanical shifter mounted on the center console does move the transmission into Park.

JettaRed

iTrader: (1)

I would think the rope warning is that when the towing car stops, the towed car does not unless there is a rider that will apply the brakes. I still don't understand a reason for doing this.

TimC300

Putting the car in neutral while the car is moving, then throw it back into drive? I tried that in my first car when I got my drivers license, was going down a big hill so put it in neutral, I seem to remember having to pull over and completely stop because it wouldnt. I know I never tried it again.

uchu47

No need to get so defensive. Thought we are grown ups here. For those who can't read properly, once again let me reiterate that question is PURELY about objective potential technical damage, if there any. So far there seems to be no ideas why that would be the case.

This is not to encourage anyone to try or suggest stupid ideas like putting Park while driving and sorts. No idea why some people are so agitated about the subject.

And again, I am not advising or suggesting anyone should do that.

uchu47

Thank you. Certainly ideas like revving up engine before putting D are ruled out.

uchu47

I remember something similar being in Benz manual I owned years ago. Something like 40/40: you can tow benz for not more than 40km at speed not more than 40km/h. Again, not sure if there is any technical reasoning behind.

uchu47

Great insight, very interesting. Thank you.