[kristadt]

I have a 2019 1LT, V6 automatic. I got it used with 12,000 miles, and it currently has almost 19,000. Ever since I got it in mid-May, I’ve noticed an issue with (what I assume is) the clutch engaging between first and second gear on the first takeoff of a drive. It’s not a neck-breaking pause, but it’s enough to move you up in your seat. It’ll accelerate normally in first gear, and then right before it shifts to second, it’ll happen. I haven’t noticed anything that triggers it, like temperature, RPMs, etc. Has anyone else has a problem like this/what would you recommend I do?

[Jamessulivan.ap]

Try checking your car's transmission. By the way, this article may be helpful for your case: https://www.obdadvisor.com/how-to-fi...sion-problems/.

[kristadt]

Originally Posted by Jamessulivan.ap

Try checking your car's transmission. By the way, this article may be helpful for your case: https://www.obdadvisor.com/how-to-fi...sion-problems/.

I'll try that, I was just trying to comfort myself in hopes that someone was also having the issue and could tell me it was nothing. thanks for the info!

[GreatWhiteLT]

It's a known issue with the A8 auto transmission. Take it to your dealer and get the triple flush done. Usually it fixes most cars with the shudder issue but unfortunately for some it does come back.

[cmitchell17]

Unfortunately GM decided to not prioritize driveability when they made and calibrated this transmission, and unfortunately as well there is almost nothing we can do about it. I think the issues may be solvable by re tuning only, however the cheapest readily available commercial software to tune it with lacks access to the specific parameters we need to fully fix the issues.

The bad driveability is made worse by having a rear wheel drive car and a two piece driveshaft and loose (good for vibration and harshness) driveline parts.

I think the issue you are describing is when you are decelerating and come to a rolling stop about 3-5 mph, then you push the gas to accelerate again. The transmission is programmed to hold 3rd gear all the way to around 5 mph then directly downshift to 1st and skip second gear. My guess is this causes a lack of fluid volume to engage a certain clutch, and when you go to re accelerate and shift from 1st to second, there is a lack of clutch fluid and this causes the clutch that is engaging for second gear come on slowly, while the clutch that releases for 2nd gear disengages normally. This causes a very slight and temporary neutral feeling at basically the transmission goes into neutral until the engaging clutch catches up due to the lack of fluid fill volume.

This is just one of the several driveability issues the 8L90 or 45 has. I believe this issue is mostly mechanical and GM may have tried to program around it, but they probably thought people didnt care enough so they prioritized early torque converter lockup and other things that decrease driveability.

Is the issue you are describing feel like the shift flares up and the rpms rev up a little then it shifts?

[JP2017SS]

My transmission does this too, i've had the triple flush and added the Range Technology AFM Disabler, both didnt help much. The only thing that i have noticed that helped was letting the car warm up good before driving in the morning, still does it but not as bad or as long.

[arpad_m]

Originally Posted by cmitchell17

Unfortunately GM decided to not prioritize driveability when they made and calibrated this transmission, and unfortunately as well there is almost nothing we can do about it. I think the issues may be solvable by re tuning only, however the cheapest readily available commercial software to tune it with lacks access to the specific parameters we need to fully fix the issues.

The bad driveability is made worse by having a rear wheel drive car and a two piece driveshaft and loose (good for vibration and harshness) driveline parts.

I think the issue you are describing is when you are decelerating and come to a rolling stop about 3-5 mph, then you push the gas to accelerate again. The transmission is programmed to hold 3rd gear all the way to around 5 mph then directly downshift to 1st and skip second gear. My guess is this causes a lack of fluid volume to engage a certain clutch, and when you go to re accelerate and shift from 1st to second, there is a lack of clutch fluid and this causes the clutch that is engaging for second gear come on slowly, while the clutch that releases for 2nd gear disengages normally. This causes a very slight and temporary neutral feeling at basically the transmission goes into neutral until the engaging clutch catches up due to the lack of fluid fill volume.

This is just one of the several driveability issues the 8L90 or 45 has. I believe this issue is mostly mechanical and GM may have tried to program around it, but they probably thought people didnt care enough so they prioritized early torque converter lockup and other things that decrease driveability.

Interestingly, I had the 8L45 for a while, then the 8L90 since March 2018, and there is a marked difference in their behavior. The 8L45 would make the car lurch a bit back and forth every time after the (jerky) 3->1 shift (more when on an incline), and the very first R->D shift while still cold was accompanied by a marked screech.

At the same time, the 8L90 has a perfect 3->1 downshift, R->D is almost perfect with a tiny little noise when and only when the trans is really cold, plus I'm not seeing this 3->1, re-accelerate, 1->2, neutral feel sequence you describe at all.

Do you think or know if there is a difference in programming between them, or is this just luck of the draw? Fluid volume is the same, isn't it?

(My 8L90 is now tuned, but its behavior didn't change with respect to the above after the tune.)

[cmitchell17]

Originally Posted by arpad_m

Interestingly, I had the 8L45 for a while, then the 8L90 since March 2018, and there is a marked difference in their behavior. The 8L45 would make the car lurch a bit back and forth every time after the (jerky) 3->1 shift (more when on an incline), and the very first R->D shift while still cold was accompanied by a marked screech.

At the same time, the 8L90 has a perfect 3->1 downshift, R->D is almost perfect with a tiny little noise when and only when the trans is really cold, plus I'm not seeing this 3->1, re-accelerate, 1->2, neutral feel sequence you describe at all.

Do you think or know if there is a difference in programming between them, or is this just luck of the draw? Fluid volume is the same, isn't it?

(My 8L90 is now tuned, but its behavior didn't change with respect to the above after the tune.)

I really don't know but it bothers me, I don't have much transmission knowledge besides what I've been able to pick up here and there, but I think there are pretty significant differences between the 45 and 90. I have a copy of the service manual with the diagrammatic, but its really low quality and you can't really tell anything from it. I really want the ability to full flash the TCM, then we could try the operating systems from the CTS-V and other Cadillacs and the Corvette and ZO6.