When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
^^^....I have observed a slight loading of the drivetrain when going from Neutral to Drive and can hear the mechanisms actuating but nothing like an automatic transmission. So there is likely some torque being transmitted through clutch pack but it is miniscule and could be attributed to fluid shear.
I would assume that when transitioning from neutral to drive, the shift forks need to push some shafts or gears to mesh, that are otherwise not engaged. With manual transmissions, there is sometimes a position where the gears wont mesh,especially if going into reverse without synchronizers, and you have to let the clutch out a touch to spin the tranmission to a position where the gears can mesh. That may be the reason you (and I ) feel a slight motion when shifting the C8 from neutral to drive - the clutches engage enough to slowly spin the gears during the transition. Even then, following your logic, once that is accomplished, the computer could still then disengage the clutches after the shift is completed (and your foot has to be on the brake for that shift to happen).
It is not clear if or why the clutches would be "slightly" engaged while in drive with the brake depressed, but if it is done that way, it would mean to me that it was intentional - not an accident. Therefore, going into neutral under that condition would seem to circumvent whatever was intended with that design.
So, I ask the question, if the computer has the ability to disengage the clutch why do you think the computer partially engages the clutch pack while stopped with your foot on the brake?
Assume they control activating pressure with rpm. And I don't for know sure just what they do. It just "feels to me" when I modulate the brake when crawling and stop it's never disengaged. Also basing it on the Tadge statement when asked about clutch wear from stopping he just said it's not a problem as it can handle when he could have said it's disengaged!
^^^
I probably shouldn't have said no engagement of the clutch. With a wet clutch there can be some torque transmitted through fluid shear even if the plates aren't making contact. And I admit that I haven't seen anything documented about the details of the idle creep operation. I'm basing this on my observations, knowledge of automotive system and engineering, and combining them with logic. But lets look at what we do know.
The computer has the ability of being commanded to disengage the clutch pack by pulling both paddles back. So now the question is why would the computer partially engage the clutch while the car is stopped with your foot on the brake if it has the ability not to. There could be valid reasons (i.e., keep the drivetrain loaded so there isn't an audible clunk when taking up the slack in the drivetrain). But from my observations loading (if any) on the drivetrain is so miniscule that it doesn't cause a fluctuation in RPM between engaged and disengaged.
I have observed a slight loading of the drivetrain when going from Neutral to Drive and can hear the mechanisms actuating but nothing like an automatic transmission. So there is likely some torque being transmitted through clutch pack but it is miniscule and could be attributed to fluid shear.
As I mentioned, once the car is warmed up there is no perceivable momentary fluctuation in RPMS when you pull the paddles back with the car in gear and your foot on the brake or when you release them. Nor is there a RPM fluctuation when you go back and forth between Neutral and Drive. So if there is any loading on the clutch pack it is so small that the computer can compensate without causing a fluctuation in RPMs. However, I have noticed a fluctuation when the car is cold possibly due to thicker fluid. The only observable change in RPMs I have noted is when I let my foot off the brake with the car in gear.
So, I ask the question, if the computer has the ability to disengage the clutch why do you think the computer partially engages the clutch pack while stopped with your foot on the brake?
This should satisfy the slipping or not question as it was answered directly by Tadge Juechter:
Corvette Forum Gets C8 Scoop from Chief Engineer Tadge Juechter By Brett Foote - August 30, 2019
Thanks to Corvette Forum Member 16/C7Z we know a lot more about it. That’s because he was in attendance at Corvettes at Carlisle, where he was able to interview Corvette Chief Engineer Tadge Juechter in person. Even better, he posted the entire thing in this thread for everyone to soak in!
“The clutches are slipping ever so slightly at idle in gear while stopped. There’s no effective wear on the clutch packs due to the low torque applied. It will function similar to the conventional automatic in traffic. The clutch packs should last the life of transmission.”
PS:Knew I recalled reading that statement but when? One properly worded Google Search found this morning! 1st thing in the list! Google is amazing, a bit scary but amazing. At 79 there are somethings that I remember. Usually trivia like this!
SIDEBAR
Another piece of Trivia was in that Thread, the date Kerbeck stopped taking 2020 Corvette orders! August 23, 2019. Funny, as the other large Corvette sellers continued to take orders they stopped well before what GM had told them was their allocation of ~1400 from prior years sales. That was BEFORE the strike and pandemic! But I also recall GM had warned even at that time they would not be able to meet their prior allocation estimates. It was not until ~February 2020 that GM gave a formal allocation reduction to all dealers of ~half their initial estimate. It affected me as I had placed my "hold-a-spot" order in late July 2019. Was concerned I would not make the 2020 MY and be forced into a 2021. The color I picked, LBR was no longer going to be offered and the 1st artist renditions of Red Mist Metallic looked bad! Turned out it was actually a very good color and I would have selected. But with all the flashy colors I frankly don't think look good for a "big" car like the C8, it was about the only one! I only got my 2020 September 2nd because GM extended the last production of 2020 MY way past their normal mid calendar year! Kerbeck was, as they had been for many years, the largest dealer of 2020 MY Corvettes. With GM's extending production they sold 866.
This should satisfy the slipping or not question as it was answered directly by Tadge Juechter: “The clutches are slipping ever so slightly at idle in gear while stopped. There’s no effective wear on the clutch packs due to the low torque applied. It will function similar to the conventional automatic in traffic. The clutch packs should last the life of transmission.”
Thanks, Jerry! I reviewed the link and in it, Tadge is also quoted as saying "I also like to pull both paddles while slowing down to a stop, i like to coast."
So now I see where the idea of pulling both paddles at a stop came from. But it has me wondering exactly what the double paddle de-clutch is doing. Perhaps it also is just pulling the clutches to the same point as the full stop at idle where the are slipping "ever so slightly". In other words, once at a full stop, perhaps there is no difference between pulling the paddles or not. The manual does describe it as a "declutch" , "similar to neutral" - note similar but not the same as neutral. Tadge said he was doing it because he liked to coast - not because he was saving the clutches or saving gas.
Have you guys ever ridden motorcycles? Especially on my dirt bikes the wet clutch drag in gear with the clutch level pulled is a very obvious and well known phenomenon. Everyone knows you want to shift into neutral before trying to kick start a bike otherwise you're just working too hard. I'm sure this is the same thing the C8 is experiencing.
Thanks, Jerry! I reviewed the link and in it, Tadge is also quoted as saying "I also like to pull both paddles while slowing down to a stop, i like to coast."
So now I see where the idea of pulling both paddles at a stop came from. But it has me wondering exactly what the double paddle de-clutch is doing. Perhaps it also is just pulling the clutches to the same point as the full stop at idle where the are slipping "ever so slightly". In other words, once at a full stop, perhaps there is no difference between pulling the paddles or not. The manual does describe it as a "declutch" , "similar to neutral" - note similar but not the same as neutral. Tadge said he was doing it because he liked to coast - not because he was saving the clutches or saving gas.
1st, Tadge said he was driving the DCT that way for the same reason I did for a month! He had always driven a stick! I was weening myself off of 60 years of EVERY DD having a 3rd pedal.
My understanding is when you pull the paddle it disengages the clutch completely. Pull both and it disengages both. The dash display shows it's in NO GEAR. Can rev the engine.
Let go of the left paddle as I did when it slowed because by definition when it's below the speed that 1st gear will engage the 2nd gear clutch IS Disengaged- has to be.
So I held the right paddle keeping 1st gear from engaging (could see that on the dash NO 1st gear showing.) Prior to the green light I often released the right paddle. 1st gear showed as being engaged and when I released the brake it behaved like a "slushbox" automatic.
It appears from his statement with ~80% of the folks who bought Corvettes with an automatic they had the same feel. It's not really, more like with my manuals slipping the clutch when on a slight grade but feels similar. As I say now that it's so smooth I don't bother. Driving in Z Mode or My Mode I just treat it like an automatic when I stop!
That is my understanding of what happened when I was pulling the paddles and now when not.
Thanks, Jerry! I reviewed the link and in it, Tadge is also quoted as saying "I also like to pull both paddles while slowing down to a stop, i like to coast."
So now I see where the idea of pulling both paddles at a stop came from. But it has me wondering exactly what the double paddle de-clutch is doing. Perhaps it also is just pulling the clutches to the same point as the full stop at idle where the are slipping "ever so slightly". In other words, once at a full stop, perhaps there is no difference between pulling the paddles or not. The manual does describe it as a "declutch" , "similar to neutral" - note similar but not the same as neutral. Tadge said he was doing it because he liked to coast - not because he was saving the clutches or saving gas.
This is part of my point. There doesn't seem to be any difference between pulling both paddles back and stopped with your foot on the brake. So the the clutches could also be "slipping ever so slightly" with both paddles pulled back. He also states that "There's no effective wear on the clutch packs due to the low torque applied". This would be consistent with how a motorcycle wet clutch pack operates when declutched. There is still a little drag from the clutch pack but it is very small. It is just inherent in the design of a wet clutch pack.
Try that with just the brake pushed hard and it will try to move forward! Will have to try with my "just right paddle pulled."
Not to make it any more complicated, just food for thought. My Ferrari DCT F-430 goes to neutral when you momentarily pull both paddles. If traveling it will stay in neutral until you pull the right paddle, then will go to the appropriate gear. If stopped it will stay in neutral until you pull the right paddle. If you are stopped and in neutral without your foot on the brake it will shift to first after 20 seconds. Weird.
Try that with just the brake pushed hard and it will try to move forward! Will have to try with my "just right paddle pulled."
OK, I should have said stopped with your brake and not applying throttle. Yes, the car will try to move if you apply throttle
Here's another thing to try. With the car stopped in gear on level ground, pull both paddles back and note that the RPMs don't increase. Now let off the brake pedal and note that the car doesn't move and the RPMs don't increase. Now let off the paddles. The RPMs will start to increase and the car will start moving, in that order. If there were constant significant torque on the clutch pack the car would start to move and then RPMs would increase similar to how a car with an automatic transmission works.
This is part of my point. There doesn't seem to be any difference between pulling both paddles back and stopped with your foot on the brake. So the the clutches could also be "slipping ever so slightly" with both paddles pulled back. He also states that "There's no effective wear on the clutch packs due to the low torque applied". This would be consistent with how a motorcycle wet clutch pack operates when declutched. There is still a little drag from the clutch pack but it is very small. It is just inherent in the design of a wet clutch pack.
Note that the following, in this post was with the car cold - but I got a different results later when I tried it with the car warmed up. I put that in post 57 below.
I just tried the following tests: 1. Car idling (and not necessarily warmed up), foot on brake, shifting between N and D, there is definite sound (most of the time) and a definite feel of the car wanting to move forward when shifting to D. I can't say there was a clear change in RPM. This is repeatable. Then shifting between R and N, there is a definite sound, and a feeling that the car wants to move backward when shifting to R. This is repeatable. I cant say there was a clear change in RPM. 2. With car idling, foot on brake, in drive, pulling both paddles back, and then releasing both, there is no perception of motion, there is no sound, and there is no observable RPM change.
My conclusion from this is that at idle, in D, with the brake on, there is either a) no difference in clutch engagment with, or without paddles pulled, or b) the difference in clutch position, with or without paddles pulled is negligible. And also, when pulling and releasing both paddles, the absence of the noise heard when going between N and either R or D, tells me that pulling both paddles is not the same as selecting N neutral.
I am also aware that when in drive, with the foot on the brake, if I depress the gas pedal, while holding the brake, the car wants to move forward. I believe what is happening is the the clutch(s) are starting to engage more as the pedal is depressed.
Last edited by Andybump; Apr 22, 2022 at 09:23 AM.
Try that with just the brake pushed hard and it will try to move forward! Will have to try with my "just right paddle pulled."
Just was in town and tried several things:
Yep pull both paddles and it's in neutral. Can tell as the dash does not display that it's in a gear. Stop. release the left paddle and it stays in Neutral. You can rev the engine. Try that with just the brake pressed hard and as expected the rpm's increase and it's trying to pull the car forward.
Tried releasing the right paddle and holding the left and again stays in neural as you can see buy no gear selected and you can rev the engine to whatever. So it's not just the right paddle but either as someone stated. Programmers can do whatever they want BUT it's staying in Neutral until both paddles are released.
Just was in town and tried several things:
Yep pull both paddles and it's in neutral. Can tell as the dash does not display that it's in a gear. Stop. release the left paddle and it stays in Neutral. You can rev the engine. Try that with just the brake pressed hard and as expected the rpm's increase and it's trying to pull the car forward.
Tried releasing the right paddle and holding the left and again stays in neural as you can see buy no gear selected and you can rev the engine to whatever. So it's not just the right paddle but either as someone stated. Programmers can do whatever they want BUT it's staying in Neutral until both paddles are released.
I'm not convinced the transmission is actually shifting into Neutral when both paddles are pulled back vs just fully declutching. If you were doing the Rapid Exit maneuver I don't think you would want the computer to first have to shift into gear and then "dump the clutch".
But I do now agree there is something more going on when you're stopped with your foot on the brake vs pulling both paddles back. I went on a drive today and decided to play around with this a little more. I found if you released the paddles while stopped you can feel the drivetrain get preloaded. Not as pronounced as when you shift between D, N, and R but there is something going on, just not enough to make the RPMs fluctuate. And you don't feel anything when you pull the paddles back. It appears that the computer applies just enough torque to preload the drivetrain to take up the slack.
But there is definite idle creep engaging once you release the brakes when you are stopped. The RPMs increase to ~1000 RPM as the car accelerates.
Discovered something interesting today while sitting at a traffic light. Regarding the discussion of how engine rpm changes when in gear vs in neutral. I noticed that when switching from D to N the revs actually appear to drop a little bit, not rise as one might expect. I repeated this several times, and it was consistent.
I then put the tach in numerical mode, displaying actual rpm at idle. With the transmission in neutral, the revs averaged right about 545 (the number is constantly changing, but it varied right around this number. Switching to D, the revs averaged right about 555. Ten rpm higher. The ECU is clearly increasing throttle slightly when at idle in D. Is that to compensate for the drag of the clutch? Don't see any other reason to program it that way.
I'm not convinced the transmission is actually shifting into Neutral when both paddles are pulled back vs just fully declutching. If you were doing the Rapid Exit maneuver I don't think you would want the computer to first have to shift into gear and then "dump the clutch".
Yes, I'm sure that (declutching) is what it's doing, not shifting into neutral.
Originally Posted by Enderthex
Have you guys ever ridden motorcycles? Especially on my dirt bikes the wet clutch drag in gear with the clutch level pulled is a very obvious and well known phenomenon. Everyone knows you want to shift into neutral before trying to kick start a bike otherwise you're just working too hard. I'm sure this is the same thing the C8 is experiencing.
That sounds logical, were it not for Tadge specifically saying they designed in "creep" by letting the clutch slip a little bit when stopped. The drag of the fluid, especially once warmed up, wouldn't be enough to make a 3600 pound car "creep" like a car with a regular automatic. Even on a motorcycle, once the oil is hot the drag from the clutch is very slight.
I'm not convinced the transmission is actually shifting into Neutral when both paddles are pulled back vs just fully declutching. ...
Possible BUT would think if that were true the dash would be showing it's in a gear, like 1st.
But programmers can do whatever they like or misread the poorly written instructions!
SIDEBAR
Recall my over 1 year raving about my early 2014 C7 M7 where the programmer had no good option (as my C6 had) AND included an option that the seat moved to the setting for your FOB as soon as you opened the door! I called it the Superman Option as had to be faster than a speeding bullet to use it! Until ~2015 when they developed a software update workaround, you had to hold your memory button to get the seat in position. Finally eliminated in 2016!
I developed a two hand approach to starting the car. Holding my #1 button with my left hand while I buckling my belt with my right as the seat moved forward! The workaround software update was a bit silly, had to press the start key twice so I never installed the software update for the 3 1/2 years I had the car. My method was faster!
I accused GM of outsourcing the software to someone who never drove a car!
Discovered something interesting today while sitting at a traffic light. Regarding the discussion of how engine rpm changes when in gear vs in neutral. I noticed that when switching from D to N the revs actually appear to drop a little bit, not rise as one might expect. I repeated this several times, and it was consistent.
I then put the tach in numerical mode, displaying actual rpm at idle. With the transmission in neutral, the revs averaged right about 545 (the number is constantly changing, but it varied right around this number. Switching to D, the revs averaged right about 555. Ten rpm higher. The ECU is clearly increasing throttle slightly when at idle in D. Is that to compensate for the drag of the clutch? Don't see any other reason to program it that way.
I agree that something is going on to load the clutches "ever so slightly" (in Tadge's words) when stopped in gear with the brake applied. It appears to be loading just enough to take the slack out of the powertrain.
But when you release the brake without applying gas then there is definitely some computer intervention going on to provide propulsion.
Just a note on holding only one paddle to hold neutral, after a short time (like 60-90 seconds, I haven't timed it) it will go back to drive when holding just one paddle so keep the foot on the brake and pay attention when you're using this technique.
.......I found if you released the paddles while stopped you can feel the drivetrain get preloaded......
That is the result needed to confirm that there is a difference when idling, with the brake on, between paddles pulled, and paddles not pulled. And, that being the case, it means that pulling both paddles under that condition does (I think) reduce clutch drag, however negligible it may be. I did not get that result during my test, but mine was performed shortly after a cold stop, not after being driven and fully warmed up. I also think it does not go to neutral - it is called a "double paddle declutch similar to neutral". Declutch is the operative term.
I notice something else about rapid exit mode (from the double paddle declutch) while reviewing that section (again). While we have noted that after pulling both paddles, the car will not "exit" the "double paddle declutch" condition until both (not just one) paddles are released, the discussion that follows regarding rapid exit and standard exit (from the double paddle declutch condition) seems to say that both paddles have to be released at the same time for the rapid exit mode, and that the standard exit will happen if the paddles are not released at the same time. I think it suggest that one should not pull both paddles, release one, and then subsequently attempt the rapid exit procedure (which involve full throttle) by releasing the remaining paddle. Not that anyone would attempt that......
