I have tried this and it selects the "correct" gear suitable for that speed and mode (normal, sport etc) that you're in.

When stationary on the brakes, if I shift from N to D, I can clearly feel something engage/move in the drivetrain. If this is not the clutch selecting 1st gear and partially engaging (ie dragging) to allow for crawl, then why is there a movement?

 

My belief is that the two paddle pull for neutral is there for those who like to move into neutral at a light (or whenever). And since it works in auto or manual PDK it makes any shift lever action unnecessary. Hitting gear up paddle (or shift up on the shift lever when in manual pops you back to the appropriate gear).

But then again, if the reason for going into neutral when stopped is to avoid pressing on the brake, well you are a lazy driver. It isn't always obvious sometimes that you are on a slight slope backwards. And I hope I'm not behind you as I can't stand the nimrods who are always rolling backwards toward me when I'm behind them.

Its like basic common sense manual driving technique.. Push the brake and clutch at a light. and if you like to go into neutral, then at least keep your foot on the brake.

 

No offense but isn't this quite obvious?

 

This whole thread is ridiculously obvious ... But people are asking questions and don't seem to have a grasp of how to use neutral and a brake... So uh no offense right back at you... what's your point....????

 

I'm not offended, just think it's obvious to have your foot on the brake at a stop light on an incline. I do agree that this thread is ridiculously obvious.

 

No duh.. My comment was inspired by inane posts about it being tiring keeping foot on brakes at lights,, and a long discussion about wear on drive train components..

 

OFFCOURSE I put my PDK in Neutral when I'm at a traffic light ! I hate standing still with my foot on the brake the whole time, I want to be able to move and relax my legs when stationary at a traffic light.
Maybe because I've been driving MT for decades, and still in my daily drivers. You don't leave it in gear with the clutches depressed with a manual at the traffic lights, so why would you do that with a PDK ?

 

Cabbies do this all the time. I seriously doubt it saves any fuel whatsoever. The car idles at the same speed in neutral or park, as far as I can tell. The chunk ka chunk of the door looks locking and unlocking drives me crazy.

 

It may be obvious to put the foot on the brake at the red light. But I don't think there is a definite answer to whether the PDK clutch is partially engaged or not when stopped with brake down? The car can crawl forward even before the brake is completely released and to me that means that the clutch may be partially engaged and dragging against the brake.

Does any one have the definite answer to this obvious question?

 

So true, so true...could be a Cadillac, a Lexus or MBZ, whatever...its still just an automatic transmission...would you do this in a big sedan?

 

The OP's question referred to the basic question of "what was better for the gearbox".. Leaving it in gear or or putting it in neutral.

What is obvious is that any reasonable design of an "Automatic Transmission" (call it what you want but that is what it is) is not going to require that you put the damn thing in neutral when stopped (or creeping). otherwise risk significant premature wear. I might believe otherwise if saw anything in the manuals or literature that implied you needed to take this action (i.e. neutral) which would be non-intuitive for an automatic transmission type vehicle. The only thing that I found addressed was not using the engine/transmission to hold yourself on a hill, and the recommendation to use the brake.. Which is pretty much the same recommendation for a torque converter based auto.

But to address the question, is the clutch engaged? The answer is YES, if the car is moving forward, then the clutch is at some level "partially engaged"... at least while it is moving forward.

However, the mistake would be to assume that the clutch it is designed just like a traditional manual transmission where the clutch is designed to be either engaged or disengaged. and any prolonged partial engagement should be minimized... otherwise you are burning the clutch up. (for example just partially engaging the clutch to hold your position on a hill or as you mentioned "creeping" along..

Clutches can be design to gradually engage so that at lower engine speeds there is very little or no transfer of torque (i.e with foot on break or just barely moving).. they effectively slip.. The PDK and most larger dual clutches.. uses a wet clutch system that sit in a bath of oil that helps with cooling, and I would presume by design can sit there at idle, not moving or creeping all day. In effect the clutch design allows it to replace the torque converter in a traditional automatic, just a lot quicker and more efficiently without the efficiency losses.

It isn't that the PDK clutches don't wear, it is just they are designed in such a way that whatever wear occurs (during normal use) it will still exceed the life of the transmission. So yeah.. maybe putting in neutral minimizes the wear on the wet clutch.. but who cares since the clutch is not considered a replaceable item and designed to last longer than the transmission anyway under normal use (i.e. stop and go traffic). A torque converter wears to some extent in a traditional automatic, but just like the dual clutch it is designed to last as long as the transmission.. So you could make the same argument that putting a traditional auto in neutral will save your torque converter.

This doesn't directly address the question.. but the Leno garage video is kind of interesting and talks a little about the PDK and the dual clutch concept. If you go to about 4:42.. they take apart the clutch itself.

http://thesportscarguys.com/2013/03/...e-apart-video/

 

Thanks for the reply. I actually wasn't aware that the clutch in the PDK is considered a non-replacement part.

If we have extablished that leaving the PDK in "D" results in a small, albeit insignificant, amount of wear, then is there any down side to shifting into N? I have seen some argue that the act of shifting between D and N at every red light results in more wear?

If the PDK is engineered to withstand being left in D while stationary, then surely it is also engineered to withstand being shifted between D and N many many times without ill effects?

 

It's an automatic in function, but an Automatic transmission has a torque converter.

The PDK is a DCT or technically an automated dual clutch transmission.

I wrote a two-part article on transmissions. To use the term "automatic" interchangeably for the two among journalists is misleading and unprofessional.

For instance, the Z-06 and Hellcat will have automatics but not DCTs.

 

I don't think there is any downside to the PDK itself going into N.. If there was a downside (reliability) it would probably be related to the mechanical reliability/durability of the PDK shift lever/linkage itself. (I am not saying I think there is a robustness issue with it, just saying that would probably be more significant than say, just using the simultaneous paddle method).

If the shift linkage is as mechanically robust as say a traditional M7 linkage then I'm sure it is fine, I just don't know if the use expectation of the PDK shift lever is intended to go from Man -> Auto -> Neutral and back tens of thousands of times (or from D -> N and back). And I distinguish this mechanical action from simply the +- shifting with the shift lever in Manual which I'm sure PDK is designed to get used repeatedly..

My only experience with that kind of things was years ago on an Automatic Mustang going from D to 2,1 and back on a regular basis and the damn linkage eventually came apart. It just wasn't really designed to be used as a continual shift device. But I don't want to compare a 1969 mustang to a 2014 Porsche..

So I'm not sure if the folks who use neutral on PDK do it via the shift lever or via paddles, I'm assuming paddles as going to N with the shift lever is kinda awkward (IMHO) when in manual mode. But as I'm learning people PDK in a variety of ways.

My guess is however, it doesn't matter.. You can probably use it anyway you want without worry.

 

I don't know that I would directly couple automatic transmission and torque converter together. The torque converter is just the most common way an automatic transmission to implement the coupling of engine torque to the driver train.. In the advent of more complex electro mechanical and computerized systems, things like DCTs become possible. So to me a DCT and Torque converter tranny are both automatic transmissions. (I just think people are sensitive to the word "automatic" since it is historically almost a derogatory term in the performance car world).

I don't think anyone is arguing that DCT and traditional torque converter based transmissions are different animals. But they both provide the same general functions.. and that is the function we typically refer to as "Automatic Transmission". And as such there is a general expectation that to an end user they are should behave similarly in the most general of senses. (eg two peddles, using only your brake to stop and not needing to do any shifting other than going into D, R or Park.

Even in manual mode, the DCT and torque converter transmissions at a general level behave similarly in that they are sequential gear transmissions.

Of course the comparison stop quickly once you get past basic functionality and start talking about performance and efficiency.. as well as the more sophisticated capabilities of the dual clutch..