[wwiiavfan]

Like the title says, anyone else seeing a hesitation when acceleration thru a rolling stop, like at a roundabout? Seems like when I nearly come to a stop but not quite, the trans can’t seem to figure out what gear it wants to select, then suddenly accelerates away. 🤔

[speedup]

Mine does this too, this A8 does so much weird stuff, I have quit paying attention to all its weird quirks

[arpad_m]

Guess I'm lucky or maybe something was done to the newer 2018's because mine doesn't display any of these (had a 2LT previously and its A8 was also quirky). The only time I even notice the trans is not the extension of my mind is when I need to back off after a pull and it still wants to go on, keeping revs higher for me.

[JaxChris]

Wait until you pass 10-15k miles, then you'll feel all of it.

Trans jerk on downshifts at low speed (most 3-2 and 2-1 shifts)
Trans jerk on reverse (long delay in converter lockup)
Trans jerk on low speed 1-2 upshifts (same feeling as reverse)

People say it is just the first shift of the day, but if you have been driving and then enter a parking lot to look for a spot, as you turn between rows you will get jerked and lunged around each time you stop/start at responsible low speeds.

The torque converter and the lockup solenoid on the 8Lxx is utter trash and GM knows it already. They won't do anything about existing inventory because every car with the 8-speed trans would be eligible for repair and replacing the torque converter is too costly for them. And since a jerking motion isn't going to cause an accident resulting in a dead driver, the actuaries won't authorize the funds. The 8-speed in the 2019 MY vehicles are receiving the revised converter and programming to fix the problem.

Vehicles affected by the 8Lxx crap converter and poorly compensating software updates:
'16-'18 Camaro (moving to 10-speed & revised 8-speed in 2019)
'15-'19 Corvette (different converter, less complaints)
'15-'18 Silverado/Sierra (moving to 10-speed & revised 8-speed in 2019)
'17-'19 Colorado (different converter, less complaints)
'15-'17 Yukon/XL (moved to 10-speed in 2018)
'15-'17 Escalade (moved to 10-speed in 2018)
'16-'18 CT6 (moving to 10-speed in 2019)
'16-'18 CTS (being discontinued)
'16-'18 ATS (being discontinued)

If GM was so sure the transmission wasn't the problem on these vehicles, then they would have stuck with the original (and highly publicized) 8L90 without modifications in these refreshes. The 10-speed gets reduced MPG, which is contradictory to their stance that they think EPA targets for 2026 shouldn't be dropped and they will continue increasing MPG with each new and refreshed product.

An aftermarket company is going to have to come up with a better built converter to service existing 8L90 duds and tuners are going to have to help as well because part of the problem is in the software that is trying to make up for poor converter performance.

[arpad_m]

Originally Posted by JaxChris

Wait until you pass 10-15k miles, then you'll feel all of it.

Trans jerk on downshifts at low speed (most 3-2 and 2-1 shifts)
Trans jerk on reverse (long delay in converter lockup)
Trans jerk on low speed 1-2 upshifts (same feeling as reverse)

People say it is just the first shift of the day, but if you have been driving and then enter a parking lot to look for a spot, as you turn between rows you will get jerked and lunged around each time you stop/start at responsible low speeds.

The torque converter and the lockup solenoid on the 8Lxx is utter trash and GM knows it already. They won't do anything about existing inventory because every car with the 8-speed trans would be eligible for repair and replacing the torque converter is too costly for them. And since a jerking motion isn't going to cause an accident resulting in a dead driver, the actuaries won't authorize the funds. The 8-speed in the 2019 MY vehicles are receiving the revised converter and programming to fix the problem.

Vehicles affected by the 8Lxx crap converter and poorly compensating software updates:
'16-'18 Camaro (moving to 10-speed & revised 8-speed in 2019)
'15-'19 Corvette (different converter, less complaints)
'15-'18 Silverado/Sierra (moving to 10-speed & revised 8-speed in 2019)
'17-'19 Colorado (different converter, less complaints)
'15-'17 Yukon/XL (moved to 10-speed in 2018)
'15-'17 Escalade (moved to 10-speed in 2018)
'16-'18 CT6 (moving to 10-speed in 2019)
'16-'18 CTS (being discontinued)
'16-'18 ATS (being discontinued)

If GM was so sure the transmission wasn't the problem on these vehicles, then they would have stuck with the original (and highly publicized) 8L90 without modifications in these refreshes. The 10-speed gets reduced MPG, which is contradictory to their stance that they think EPA targets for 2026 shouldn't be dropped and they will continue increasing MPG with each new and refreshed product.

An aftermarket company is going to have to come up with a better built converter to service existing 8L90 duds and tuners are going to have to help as well because part of the problem is in the software that is trying to make up for poor converter performance.

Thanks for the extensive info. The interesting thing is the 2LT was also a 2018 and I had these exact three symptoms you list, although to a mostly tolerable extent, from day 1. Okay, that was the 8L45 and not the 8L90, but I imagine the overall design would be the same. The A8 I have now is clearly behaving much, much better, it is in fact perfect at the moment. Of course longevity is a big question mark, and I do understand your points... seems it would be best to get it tuned before things go south.

[JaxChris]

It's not just the 8L90, either of the original 8L variants appear to be prone to it. If I were to guess why this was allowed to fly; it is because they wanted to make it fit in the C7. The 10L80/90 is longer the 6L/8L casing (like it should be) and the extra length is why it can't be used in the C7.

[cmitchell17]

Do you think the jerky downshifts 3-2 and the way harder than it needs to be 2-3 is caused by the lockup tcc solenoid?

I had an 5 speed Allison as well and a 4L60 and they all had poor shift quality. You would think though with flow matched solenoids and all the extensive hydraulic engineering and modern controls, the 8L80 would shift good. I mainly think it's just do to placebo effect that you don't start really picking up on bad shift quality until you've drove a vehicle for a pretty long time. But yeah I agree the low speed driveabilty in the 8L80 and 6th gen Camaro, at least mine, is pretty horrendous, just try driving in traffic before it shifts out of first gear and press the pedal, a slight rev by all the slack in the driveline followed by a huge jerk forward. Then when you let off, a huge lunge forward. I don't understand why GM can care so much about NVH due to noise quality and dumb other things but then just makes the vehicle literally undriveable. Makes no sense to me.

[JaxChris]

I specifically called it out as a bad lockup solenoid on one of my many service visits. You put the vehicle in reverse, you feel the gear take, you apply gas pedal and about 2-3 secs later the entire car jerks violently (like you hit another car) because the lockup solenoid actuated extremely late.

Why a slushbox needs to go into lockup for reverse is beyond me. It can just suffer horrible free spinning turbine efficiency for 16-20 feet as far as I'm concerned. Who cares if the car only gets 2mpg in reverse. You're going to get it up to what... 5-7 mph anyways.

The TC and TCM really have a split personality. It will operate with lightning speed and surprisingly good precision when you pound on it. But the moment it starts up or whenever you begin to operate it like a grocery-getter navigating a parking lot it bucks like a bronco to punish you and would rather shake itself apart instead of crawl at low speed.

It could even be piss poor stall performance below 1200rpm due to insufficient fluid pressure causing a wait event for pressure to build before actuating the solenoid (low speed, low throttle shifts) and to some degree excessive viscosity (why cold start is bad, but remote start and waiting 3-4 minutes before driving lessens the amount of whiplash).

The 4L60 did have a very similar problem whenever the lockup solenoid went bad. My 1997 Camaro had that happen. Two dealers tried to tell me I broke my car before I found a shop that knew what they were doing and they diagnosed it. Took a month for the dealer to admit they misdiagnosed it and said they or GM would send me a refund for repair -- never saw that refund.

If an aftermarket street-touring converter comes out and some pro tuners put in some calibration work to go hand-in-hand with it, I think we could have our own solution.

GM is even casually mentioning the fixes to the 8L models for 2019 vehicles. New programming and a new torque converter. Hmmm.... (link below, paragraphs 8-10)

https://media.chevrolet.com/media/us...erado-dfm.html

[cmitchell17]

Originally Posted by JaxChris

I specifically called it out as a bad lockup solenoid on one of my many service visits. You put the vehicle in reverse, you feel the gear take, you apply gas pedal and about 2-3 secs later the entire car jerks violently (like you hit another car) because the lockup solenoid actuated extremely late.

Why a slushbox needs to go into lockup for reverse is beyond me. It can just suffer horrible free spinning turbine efficiency for 16-20 feet as far as I'm concerned. Who cares if the car only gets 2mpg in reverse. You're going to get it up to what... 5-7 mph anyways.

The TC and TCM really have a split personality. It will operate with lightning speed and surprisingly good precision when you pound on it. But the moment it starts up or whenever you begin to operate it like a grocery-getter navigating a parking lot it bucks like a bronco to punish you and would rather shake itself apart instead of crawl at low speed.

It could even be piss poor stall performance below 1200rpm due to insufficient fluid pressure causing a wait event for pressure to build before actuating the solenoid (low speed, low throttle shifts) and to some degree excessive viscosity (why cold start is bad, but remote start and waiting 3-4 minutes before driving lessens the amount of whiplash).

The 4L60 did have a very similar problem whenever the lockup solenoid went bad. My 1997 Camaro had that happen. Two dealers tried to tell me I broke my car before I found a shop that knew what they were doing and they diagnosed it. Took a month for the dealer to admit they misdiagnosed it and said they or GM would send me a refund for repair -- never saw that refund.

If an aftermarket street-touring converter comes out and some pro tuners put in some calibration work to go hand-in-hand with it, I think we could have our own solution.

GM is even casually mentioning the fixes to the 8L models for 2019 vehicles. New programming and a new torque converter. Hmmm.... (link below, paragraphs 8-10)

https://media.chevrolet.com/media/us...erado-dfm.html

I didn't know the tcc solenoid engaged in 1st or reverse? but I haven't logged it personally or even logged shift times to see if its on target. I would like to compare a calibration from the 8L90 on the CTSV and corvette to see if there may be some intentional "bad programming" haha I doubt this though, dosent seem like the engineering expense would be worth it. As much as it seems like its just bad logic or programming, just due to the random and unexpected nature of the shift quality, I wonder if it may be debris or different hardware components? I guess I did get a "free" trans flush at 40k due to the TCC shutter haha so I guess I got my flush. I don't have enough seat time in another manufactures car to observe shift quality as much as I should have, since I may just be really OCD about it.

[cmitchell17]

So I got curious and compared a 2016 8L90 in a CTSV to a 8L80 2016 camaro:


The green one is the CTSV and the other the Camaro, so this proves the CTSV doesn't lock the torque converter in 1st but the Camaro does. There are also slight differences in shift times, where it appears for some shifts the CTSV shifts a little bit slower at lower torque values and faster (up to .1 sec) at higher torque.

I have a 2017 so unfortunately can't reflash my TCM to try the CTV calibration out.
But to me it appears there are no significant differences in the drivability areas besides the slight increase in shift timing at the medium to low torque values.
As a side note, does anyone know if the 8L80 can skip shifts, according to the tune file it has calibration data for shifting sequentially up and down and just skipping one gear? I know in some WOT downshift situations it takes about almost 4 seconds for it from the time it goes WOT in 8th to downshift to 2nd.

Also, HP tuners has the ability to do the factory relearn and trans cleaning procedure. Unfortunately the trans learning procedure makes the TCM unresponsive and you have to pull the fuse to reset, but you can clear the adaptive values and reset. After doing this it does feel like the shitty bad drivability and unnecessary hard shifts go away for a little, but then the trans relearns the bad behavior, this may just be placebo. The trans cleaning feature would be nice to try to use, but it also doesn't appear to work

[cmitchell17]

Ok I actually take that back about the 8L80 only being able to shift sequentially and skip only one gear:



Apparently the table is there for a 8-2 downshift, although I know sometimes this takes forever. I guess it's just the hydraulic circuit has to fill.

[JaxChris]

I guess you believe me now? =)

If you have HPtuners unlock your TCM you should be able to play around in there and disable lockup in 1st gear. Hopefully you can do the same for reverse. Why it even applies lockup in reverse is beyond me, but as soon as you have that delayed engagement happening, you're going to hate every cold start that requires you to backup.