2016 8sp auto?

I have the 8 speed in my 2016 Corvette Z06, it is the 8L90 which is just the higher torque rated version of the 8L45 used in the ATS, and the only real complaint I have with it is you need to do a manual 1 to 2 to 1 shift on the first start of the day while still stationary to avoid a harsh initial 1 to 2 shift because of a slow filling clutch pack reservoir. I rarely run mine in auto mode because leaving it in manual mode keeps the Z06 engine from going into 4 cylinder mode which does create transmission problems.

Programming wise it seems to work well with smooth shifts in light acceleration with very fast firm shifts under high throttle and a nice crackle from the exhaust at full throttle upshifts when there is a brief fuel shutoff to allow faster shift completion. But most of the time mine is in manual mode and I only use it in auto when I have the Range module plugged in to prevent V4 mode.

In some platforms there are definitely issues with the programming resulting in awkward shifts and busy shifting behavior. I was on the fence when buying a new pickup as to buying a 1500 series crew cab or another 2500 series diesel crew cab and ultimately I decided to go with another diesel with part of the reason being to avoid another GM engine with active fuel management and to get the very solid and reliable Allision 1000 series automatic instead of another GM 8L90 which had definitely upset some pickup owners with its shifting and general operating behavior.

I haven't heard many serious complaints about the 8L series in the ATS and CTS platforms but it has been extremely problematic in the naturally aspirated C7 generation Corvettes (regular Stingray, Z51, and Grand Sport versions) where the frequent V4 mode operation has created torque converter clutch wear resulting in shudder.

I also sometimes get a "funky" 1-2 shift. It does not seem to happen when I first drive the car but towards the end of my commute. I only have a mile or so and I am on the interstate for 25 or 35 miles, and it is after I get off the interstate that I get the funky shift. Seems to happen more in the warmer weather.

What I see is the following:

Starts out in first gear just fine
When it should shift the clutch disengauges, but the revs don't drop.
There is a pause with no acceleration.
Next gear is automatically selected and the clutch grabs very hard jerking the car forward.
Next shift and all above shifts are perfect.

I can't decide if it is the 1-2 shift that just hangs for a second or two, or if the trans is actually never selecting second, and the pause is when second should have been selected, and then the trans goes into third gear while the revs are still up.

Note I baby the gas, these are not high RPM full throttle shifts, but very easy acceleration, and are with the trans in drive. The trans is probably shifting around 2000 RPM. I have never even tried manual shifting the auto trans. The car has about 7000 miles on it.

Need2Speed said:

I also sometimes get a "funky" 1-2 shift. It does not seem to happen when I first drive the car but towards the end of my commute. I only have a mile or so and I am on the interstate for 25 or 35 miles, and it is after I get off the interstate that I get the funky shift. Seems to happen more in the warmer weather.

Click to expand...

These electronically controlled clutch to clutch automatics have multiple memory "cells" where parameters are stored for shift control under various operating conditions and it sounds like your transmission has developed a bad habit for that specific gear and operating conditions. Basically the rotational speed and rate of change are very precisely measured at the transmission input shaft, output from torque converter, intermediate shaft, and output and the controller uses these measurements to compare actual to desired shift characteristics and then adjusts rate of clutch pack apply/release and also ultimate clutch apply pressure when actual and desired diverge. Early in the life of the transmission these adjustments are made quickly and in large steps but as operating hours build the adjustment amount is attenuated as at this point it normally is only adjusting for typical clutch pack wear over the life of the transmission. If it develops a bad habit after initial operation the dealer can put it back into a "fast learn" situation so that it quickly corrects itself. If the relearn procedure doesn't work then it is likely there is a problem with the variable force control solenoid for one of the clutch packs or the clutch pack has been compromised.

In any case document exactly the conditions under which it happens and provide that to the dealer so that it can be resolved under warranty.

The only time I can confuse the similar 8L90 transmission in my Covette is when it is in automatic mode and I do a "rolling stop" at a stop sign and it isn't sure whether to do the normal 3 to 1 shift for a stop or stay in third to continue. I guess it is trying to tell me to obey the law and come to a complete stop. Otherwise it seems to have an uncanny ability to decide which gear to select which is the reason I have a Range anti-AFM module so that I can enjoy the transmission in fully automatic mode without the annoyance of V4 operation. Although I have gotten better at timing paddle shifts, in first gear redline is about 45 MPH and it reaches that very quickly. The tach has a line of guidance lights that close to help time shift actuation but the transmission is still faster in full auto mode and with the rate of RPM climb in first gear it is very difficult to time the shift perfectly without hitting the limiter.

Need2Speed said:

I also sometimes get a "funky" 1-2 shift. It does not seem to happen when I first drive the car but towards the end of my commute. I only have a mile or so and I am on the interstate for 25 or 35 miles, and it is after I get off the interstate that I get the funky shift. Seems to happen more in the warmer weather.

What I see is the following:

Starts out in first gear just fine
When it should shift the clutch disengauges, but the revs don't drop.
There is a pause with no acceleration.
Next gear is automatically selected and the clutch grabs very hard jerking the car forward.
Next shift and all above shifts are perfect.

I can't decide if it is the 1-2 shift that just hangs for a second or two, or if the trans is actually never selecting second, and the pause is when second should have been selected, and then the trans goes into third gear while the revs are still up.

Note I baby the gas, these are not high RPM full throttle shifts, but very easy acceleration, and are with the trans in drive. The trans is probably shifting around 2000 RPM. I have never even tried manual shifting the auto trans. The car has about 7000 miles on it.

Click to expand...

You have what's called flare. It's something that exists in all torque converter autos, but much more pronounced in modern ones with adaptive learning (in cases where the adapts have learned bad habits). I had the same issue and did a trans adapt reset, followed the explicit learning procedures, and now it's perfect.

Tell the dealership you've done your research and feel that a trans adapt learn/reset is in order. If they won't do it, see if you can get someone local with HPTuners to help out. It's available in the HP Tuners scanner with no licensing cost. If all else fails, I could reset for you if you feel like a roadtrip to Cleveland

EDIT: Here is the commonly referenced service article that addresses all of the common complaints. You'll see this article all over the Corvette and Camaro forums too: https://gm.oemdtc.com/6777/16-na-01...flares-2016-2017-buick-cadillac-chevrolet-gmc

Each new generation of clutch to clutch architecture from GM has increased the level of adaptation it does in response to the driver and the rest of the powertrain.

My first experience with this technology was with the Allison 1000 in my 2001 GMC diesel pickup (Allison transmission at that time was still fully part of GM). These clutch to clutch autos (no slipping bands, overrunning clutches, etc. as found in older automatics) require extremely tight control and timing as one or more clutch packs are engaged simultaneously with one or more releasing when the transmission shifts gears and if the timing isn't perfect you either end up with slipping or the worse situation where the transmission is trying to briefly engage two ranges at the same time. Part of this control comes through very precise measurement of shaft RPM at the input to the torque converter, output from the torque converter, intermediate shaft speed, and output shaft speed. From these measurements the controller adjusts engage/release timing AND both the ultimate engagement pressure along with how quickly the pressure ramps up during clutch pack apply. The results of each shift are compared to what the controller considers optimal and adjustments in timing/pressure/pressure ramp are made for future shifts to correct for undesired results.

In the early operation of the transmission the controller is in a fast adapt mode as the transmission adapts to the vehicle and powertrain but as the operating time adds up it goes into a slow adapt mode where it mostly adjusts for normal clutch wear that occurs over the life of the transmission. If it "learns" a bad habit after the first few miles then it can take quite some time to unlearn this behavior unless special steps are taken and depending upon the model the transmission may be temporarily put back into fast adapt mode and the conditions leading to the bad shift are repeated several times to learn a better set of shift parameters.

Because each one of the range changes occurs under multiple conditions (i.e. various throttle settings, load conditions, temperature, etc.) there are multiple memory sets for each range shift which is why typically a "bad" shift won't occur with every change between the two problematic gears but only when the problem conditions are met and this is one reason it can take some time to unlearn a bad set of parameters. As an example my 2001 GMC had to be put back into fast learn at around 6,000 miles to correct a somewhat rough 2-3 shift that only occurred under light/moderate throttle with a warm engine and the AC compressor active.

About the time these adapt strategies were becoming very good stringent EPA and the related CAFE requirements have resulted in the transmission programming playing an increasing role in compliance and the balance between customer preference and regulatory compliance has shifted quite a bit. This means that even a perfectly operating transmission is going to do some things we won't like as drivers and any anomaly will become more noticeable than it would have with friendlier programming. Customer preferences also vary a lot so perfect programming for one customer and/or platform will seem horrible to others. I am on my third pickup with a heavy duty Allison auto and I like the firm and sure shifting this unit provides, especially the way it keeps its torque converter locked even under high throttle operation. But someone who values cushy drivetrain performance would hate the obvious shifts of the Allison auto. The 8L90 (big brother to the 8L45 used in the ATS) has firmer shifting than the older 6L45 and I prefer the operating characteristics of this transmission in my Z06 to the "mushier" feel of the 6L45 in my 2014 ATS but that is a user preference and peoples' tastes certainly vary.

The 8 speeds do have a different feel, compared to the earlier 6 speed, with the multiple gears and more aggressive locking/unlocking of the converter clutch in meeting EPA standards. The 8L series provide faster shifting and more efficient operation via an improved hydraulic system compared to the 6L series and I like the transmission but even though it could be as smooth as the older 4 and 6 speed units the environment dictates that its personality is strongly influenced by indirect federal regulations because the transmission plays a key role in overall emissions and economy compliance. I am sure if these regulations didn't exist we would have far different transmission programming and the abomination known as AFM (active fuel management) would never have seen the light of day. The biggest issue I have seen with the 8L series transmissions is from the torque converter lockup clutch destroying modulation that is used during reduced cylinder mode to help absorb the vibration that occurs from running an engine on a less than native number of cylinders. The Range module plugged into the OBD II port in my Z06 prevents AFM from activating and results in a very responsive transmission when driven either in manual or full auto mode. I suspect Range will soon bring out a module to defeat start/stop engine operation which can be extremely annoying depending upon driving conditions and some vehicles make it very difficult to avoid this mode (i.e. some GM vehicles I have rented on trips have no off switch for this "feature" and it is only defeated by operating the transmission in manual mode).