jstkrsn

A torque converter transmission default is in lock up. There is a solenoid switch that unlocks it when you are coming up to stop so the engine will idle. I had an old car that the switch wore out or broke and the car would buck and die when you tried to stop. Well my new 2023 corvette with the DCT is doing a similar feeling thing. It doesn't die though. When coming to a stop it literally bangs into first or between 1st and 2nd, and shudders. I thought I hit something the first time it happened. It does it almost every time when I am coming to a stop. Works fine going forward. I have only 300 or so miles on it now. Anybody else have something like this happen? I read about transmission problems and I wonder if I am one of the unlucky ones.

Blindfingers

You're not having problems. The cause for the bucking is the rev match as you slow and the tranny downshifts causing the bucking. To alleviate the issue you can pull both paddles, which puts the tranny into neutral.
My 21 does it and it's something you get used to.

combatninja

I disagree. I properly functioning C8 transmission exhibits no 'banging' or 'shuddering' when coming to a stop. Take it to the dealer and get it diagnosed. I assume you lost the C8 DCT lotto. Sorry for your loss.

BigButtLover

Mine doesn’t buck or slam into any gear. All smooth. I think you have a problem.

Zymurgy

The DCT shift behavior (both up and down shifts) are dependent both on what driver mode you are in and how you drive it:

Stanimal

You are not alone. I also have this problem. It's most notable in Tour mode. Seems like the rev match doesn't spool the rev's high enough in this mode. Makes coming to a stop hard to do smoothly.

1Sikstik

Mines smooth as silk. Bring it in thats not normal

Limecat

I have about 600 miles on my 23 z51. My trans is smooth except when coming to a stop. Any shift under 20 mph is a hard shift. No banging or shuttering though.

JerryU

First, the DCT is not like a torque converter automatic. The C8 DCT is more like a standard transmission, which it is, two 4 speeds. Shifting is done just like my two C7 standard shifs! The difference is:

• hydraulic actuators, computer controlled rather than a "stick" move shift forks,
• when slowing to a stop, the clutch is not disengaged, it slips,
• when stopped it stays in 1st gear and does not go into Neutral!

As it slows to about 5 mph in 1st gear the 1st gear clutch starts to slip. Has to or the engine would stall. With your foot firmly on the brake the 1st gear is still slipping but with minimum pressure. As your foot comes off the brake the rpm and clutch engagement pressure will increase just as if you were driving a standard shift.

For the first 800 miles as that 1st gear clutch plates were breaking-in, it felt slightly jerky when going slow. I even did, as some suggested, pulled both levers that fully disengages both clutches. After that as now with ~8000 miles it's perfectly smooth. I stopped pulling both paddles after the 1st month. Not necessary.

Now when driving in Z mode, which I often do Powertrain set to Track, and apply the brakes aggressively it will downshift to 1st at higher rpm and may feel like it's a harsh downshift. One situation I must do often is leaving the 4 lane highway and turning onto our 25 mph speed limit rural road. When traffic is heavy, often, so folks coming back from Myrtle Beach including large RVs don't have to slow excessively for me I apply the brakes aggressively from ~70 mph (typical traffic speed.) It downshifts from 5th to 4th, to 3rd rev matching each, all in the blink of an eye! Love the sound. Could say it is fast harsh shifts.

You may fine, in addition to getting used to the DCT operation, it may smooth out after ~1000 miles. However if your banging and shuddering doesn't fit what I mention, see the dealer.

LucaBrasiAZ

im at 600 as well and my dct acts exactly like yours. The one thing i have noticed is it has gotten significantly better over the past couple hundred miles but still noticeable going down from 3 to 2 coming to a stop. I also notice its not as jerky if i stop quicker and not do a long rolling slow down.

MarkMeHopeful

I agree with others that a bang or shudder when downshifting is not normal behavior. Mine has never done this (now at ~3000 miles) - the rev matching on 2-1 downshift is very smooth no matter how quickly or slowly I stop. Definitely take it to the dealer and have it checked out

JDSC8VETTE

Take it out of rodeo mode.

Andybump

The Owner;s Manual wants you to have that done at or near 7500 miles. Although not in writing, a consistent message from GM representatives at seminars, on more than one occasion, is that if you change the filter early, you need to change it again at 7500, because wear in debris continues to accumulate during that entire period. In fact, the exact example given was "if you change it at 3000 miles ......" As to whether or not the warranty would be voided, that terminology was not used - however - there is a risk that warranty claim might be denied if the service was not done in accordance with the owners manual, which says AT 7500 miles.

JerryU

It's a great shifting DCT it's NOT and does feel like a "slushbox" automatic. Thank goodness! In fairness every DD I have had for 62 years before the C8 was a standard shift. Was concerned for cost reasons when it became obvious in ~2018 the C8 would not have a standard shift I was concerned. Loved my prior 5 Vetts starting in 1988 and my 2017 Grand Sport was the best of all, each being better. For cost reasons I thought the C8 might used the joint 8 speed slushbox GM developed with Ford (and they each produce separately. In fact had that been the case I would probably be driving a Porsche! Was looking (see pic!)

Apprehensive of getting the C8, I drove in Manual Mode for the 1st month getting over the 62 years of every DD having a 3rd pedal! Underkiness at slow speeds and standard shift nises. Understanding how it operates (see Post #9) could accept the slight jerkiness at slow speeds and when coming to a stop (all perfectly smooth now and when past ~1000 miles.) In fact after that first month discovered Z Mode Powertrain set to Track and no longer use Manual Mode! Love the rapid several gear downshifts with rev matching when braking aggressively (which I do often.)

Perhaps you have some mechanical issues, if after ~1000 miles it's not smoother and you learn how it's supposed to sound you will find, as I have with ~8000 miles, it great and have had no issues.

with your thought because of break-in debris, especially that 1st gear clutch smart to change the DCT filter early that requires a flush per GM requirements. When the OLM said change engine oil (mine did at 12 months with ~3000 miles) I had the dealer not only change the engine oil but also the DCT filter that GM specifies a flush prior. ALL ON GM'S DIME. In my case, next oil change, year 3, I will have the DCT filter changed again when as required by GM max 3 years ALL DCT fluid must be changed (per your Owner's Manual.) That will meet the GM ~7500 miles DCT filter change requirement AND you won't have ~8 oz of Old Fluid and Dirty Fluid in the filter housing remaining with the 11 quarts of new fluid!


This is the Pic I posted ~July 2019 on the "Standard Shift Forever" Thread before I placed my C8 order. Was looking at a Porsche Cayman 718 GT4 that was just being introduced as they finally put he engine in the middle where it belongs. It finally included a 6 cylinder engine in the Cayman (although lower power then the C8.) BUT slower 0 to 60 from my 2017 Grand Sport, don't like going backward. When GM announced C8 0 to 60 in 2.9 seconds at the July launch I placed my Hold-A-Spot order. Haven't looked back! Note was concerned the and still am to some degree about the small C8 brakes- see next pic.



Here another thing to complain about BUT correctable! Could not understand why my C8 Z51 did not stop even better than my C7 Grand Sport until Jason Fenske (Engineering Explained) interviewed the GM Corvette Brake Engineers. He found they didn't use large brakes as Porsche and Ferrari have with even smaller tires that stop significantly faster, even faster then my C7 Grand Sport for a reason. It was to stop "less skilled drivers" from causing the C8 to act like early ~60% rear weight cars and spin out, rear 1st. This PDF quotes Tadge saying when they were designing the C8 "He was Paranoid and Deathly Afraid of Oversteer he had experienced with his dad's early 911!"
http://netwelding.com/C8_Big_Brakes.pdf

hawk02

To the OP: My C8 shuddered and bucked at low speeds for the first 1500 miles. It was bad enough that I came very close to taking it to the dealer because I thought there was something wrong with the transmission. I even started a thread about it. I couldn't understand how folks were praising the DCT and claiming how smooth it shifted when mine was jerking the heck out of me. Someone responded to my thread that their C8 jerked and bucked initially but it went away after 1500 miles. So I decided to be a little more patient and sure enough as my car reached 1500 miles, the shuddering, bucking, and jerking at low speeds began to get less and less. With a little over 7000 miles on my C8, the transmission is very smooth. No shudder when slowing down and definitely no bucking and jerking at low speeds.

I believe one of the Corvette transmission engineers stated at Carlisle this summer that the transmission isn't fully broken in until 7500 miles. So my recommendation to you is give it more time. The transmission should start to smooth out as you put more miles on your car.

Rapid Z

That’s not normal at all. I think you may need a valve body replacement. My 2020 did this same thing when it was new. However my 2022 and 2023 do not. My 2020 did start getting better after about 3000 miles but I still don’t think it’s normal because my 22 and 23 were both relatively smooth at low speeds. Get it evaluated.

jstkrsn

Well I have 400 miles on the car now and the bucking or shaking when coming to stop has almost disappeared now as others have said. Just does it a little once in a while. It just took a little breaking in. I did the putting it in neutral as some had suggested and that helped a lot.

JerryU

Glad it's getting better and you're getting used to and understanding the difference between what some of us call a "slushbox" torque converter automatic and the C8 DCT that is essentially two 4 speed standard shifts operated thru two concentric clutches. One clutch for each 4 speed.

Pulling the paddles is just delaying the time it takes to get perfectly smooth! Perhaps not much but as it slips it wears the multiple clutch plates.

Using a pic, as I like to do, and understanding the 1st gear (also activates all odd number gears, 3rd, 5th and 7th) is slipping when stopped and going below ~5 mph. Has to or the engine would stall. The DCT does NOT go into neutral when stopped.

Yep that shatter you feel is the 1st gear clutch plates wearing. Also why I (and some others) recommend changing the DCT filter and performing a flush (as GM specifies) at the 1st engine oil fill. Even if like myself it only had 3000 miles. Yep GM says 7500 miles and I will have it changed again at year 3 service since the Owner's Manual says all DCT fluid must be changed AS A MINIMUM every 3 years. best IMO to get ride of the break-in debris including from that 1st gear clutch.

Both Concentric clutches have multiple plates that operate in the DCT fluid. The 1st gear clutch is the larger outer. It is engaged when stopped and crawling below ~5 mph BUT SLIPPING. Has to or the engine would stall. It's NOT like a torque converter where the engine is only connected to the transmission by fluid. No mechanical contact so it can slip with zero wear.

RonnieC6Z

I had the exact same problem with my 2020 when it was new, so the head of the service department, after driving my car, called GM and was informed that they had to do what is called a transmission flush. The car was in the shop for maybe 5 hours. This was about 2 years ago. The fix worked perfectly and have not had a problem since.

JerryU

That is one reason I had the DCT filter changed when OLM showed 5% oil life left when the C8 was 12 months old. GM procedure requires a flush BEFORE the filter change. Tech showed me what it said on the GM Service Computer, i.e. a flush is required to have possible debris put in the filter housing and filter so it can be removed with the filter and ~8 oz of fluid in the housing.

There are a number of posts similar to yours. Some said the dealer performed the flush several times.

Below is pic of Tech doing the flush. Actually, he does nothing, it's done by the GM Service Computer which is connected to the C8's OBD port and GM's computer via WiFi.

We both watched his PC as with the engine running you could hear "stuff" happening, probably valves actuating, shift forks moving etc. After ~ 10 minutes his PC screen said flush completed or some such words!