[Dave_StHelens]

Chiming in on shudder, I have experienced a slight shudder from time to time when in "D" as opposed to "M" (manual) and on a slight incline. The feeling I have when this occurs is the software that controls the shifting is attempting to keep the tranny in as high a gear as possible in order to keep the rpm's down and in so doing increase gas mileage... just thinking software update of some sort could fix the issue but perhaps that would impact advertised gas mileage and Chevy is not willing to go there...

[SuperSound]

Originally Posted by Dave_StHelens

Chiming in on shudder, I have experienced a slight shudder from time to time when in "D" as opposed to "M" (manual) and on a slight incline. The feeling I have when this occurs is the software that controls the shifting is attempting to keep the tranny in as high a gear as possible in order to keep the rpm's down and in so doing increase gas mileage... just thinking software update of some sort could fix the issue but perhaps that would impact advertised gas mileage and Chevy is not willing to go there...

You are on the right track but it's not a shudder from "lugging the engine". The TC is locked up in these cases and has a programmed amount of slip (between the engine RPM and driveshaft RPM). The issue is too much slip on the TC. Some guys have tuned out the slip valves and the issue stopped. But the real issue is not so much the slip values, but that the TC material is causing excessive slip. I'm not a auto trans expert, so anyone correct me if I misspoke.

The above is at least the prevailing theory at this point. Hopefully we will get some answers from the "Ask Al" thread.

[Dave_StHelens]

Originally Posted by SuperSound

You are on the right track but it's not a shudder from "lugging the engine". The TC is locked up in these cases and has a programmed amount of slip (between the engine RPM and driveshaft RPM). The issue is too much slip on the TC. Some guys have tuned out the slip valves and the issue stopped. But the real issue is not so much the slip values, but that the TC material is causing excessive slip. I'm not a auto trans expert, so anyone correct me if I misspoke.

The above is at least the prevailing theory at this point. Hopefully we will get some answers from the "Ask Al" thread.

Thanks for sharing that summary, great info!!

[Klayman]

Originally Posted by SuperSound

You are on the right track but it's not a shudder from "lugging the engine". The TC is locked up in these cases and has a programmed amount of slip (between the engine RPM and driveshaft RPM). The issue is too much slip on the TC. Some guys have tuned out the slip valves and the issue stopped. But the real issue is not so much the slip values, but that the TC material is causing excessive slip. I'm not a auto trans expert, so anyone correct me if I misspoke.

The above is at least the prevailing theory at this point. Hopefully we will get some answers from the "Ask Al" thread.

This is true.....Corvette forums show the manufacture and material of the T/C sheds some small amounts of debris when new. They have upgraded the T/C a few times. Also, i believe there are small screens in line with the shift solenoids that will then get clogged and affect shifting along with the long shift sequences, hence the shuddering.

We'll see what Al says.....

[Klayman]

Here is a breakdown of the shift solenoids and dampers (accumulators). I do not see any screens but the solenoids might be affected by any debris along with the accumulators.

This is from the ATRA web site on the 8L90 tranny breakdown webinar:
(PDF)

8L90 Valve body.pdf

[Klayman]

Here is another pic with solenoid ID:

[classicrockr]

Guide me here, everyone.

- when going steady at about 1400rpm, the car hesitates until I either go above/below that rpm point.

- Whenever I turn the car on after sitting all day, it seems to take a long time for the car to "idle down". Sometimes when I turn it on & then put it in drive after about 10 seconds, the car moves forward & then "shudders" or jumps forward a couple times, then the idle drops down & it seems ok.

- I never drive on any inclines, so it's hard to really test it. On flat roads, I usually have no problems when I hit the gas to pass or accelerate.

I've never had a car take this long to adjust the idle. is the torque converter the problem?

[MJinNC]

So had the TC replaced about 300 miles ago, all was great and was actually fun to drive the car again with out the shudder. Today, Got a slight prolong shudder going 57 with cruise on at about 1400 rpms. I did notice that they did tweek the rpm's to try and keep it above 1100 while cruising and the mpg has gone down about 1 mpg doing so, which I will take to eliminate it getting stuck at that low rpm. Don't know what the next thing is to do if the shudder comes fully back.

[camaro5]

Originally Posted by classicrockr

Guide me here, everyone.

- when going steady at about 1400rpm, the car hesitates until I either go above/below that rpm point.

- Whenever I turn the car on after sitting all day, it seems to take a long time for the car to "idle down". Sometimes when I turn it on & then put it in drive after about 10 seconds, the car moves forward & then "shudders" or jumps forward a couple times, then the idle drops down & it seems ok.

- I never drive on any inclines, so it's hard to really test it. On flat roads, I usually have no problems when I hit the gas to pass or accelerate.

I've never had a car take this long to adjust the idle. is the torque converter the problem?

Initial cold start high idle is for emissions control.

Find another V6 and compare to see if yours is normal.

[camaro5]

Originally Posted by MJinNC

So had the TC replaced about 300 miles ago, all was great and was actually fun to drive the car again with out the shudder. Today, Got a slight prolong shudder going 57 with cruise on at about 1400 rpms. I did notice that they did tweek the rpm's to try and keep it above 1100 while cruising and the mpg has gone down about 1 mpg doing so, which I will take to eliminate it getting stuck at that low rpm. Don't know what the next thing is to do if the shudder comes fully back.

They can't fix these for long, as you have already found.

BBB Autoline it (lemon law) and get a 2019 A10 if they pair it with the V6.

Certainly A10 coming to SS, LT no definitive info yet.

[awrj2000]

Originally Posted by MJinNC

So had the TC replaced about 300 miles ago, all was great and was actually fun to drive the car again with out the shudder. Today, Got a slight prolong shudder going 57 with cruise on at about 1400 rpms. I did notice that they did tweek the rpm's to try and keep it above 1100 while cruising and the mpg has gone down about 1 mpg doing so, which I will take to eliminate it getting stuck at that low rpm. Don't know what the next thing is to do if the shudder comes fully back.

You have 2 options if you really want to keep this car:

1: Get HP Tuners (about $500) and take the trans slip to 0% for 7 and 8 gear. This voids warranty.

I read somewhere the trans slip was added to prevent false knock...not looking for source again.

2: Go with a different transmission fluid. Again voids warranty. (I went Amsoil, but need many more miles to validate long term cure).


The GM Trans fluid looked like gray water at 23,000 miles in my car (shutter stated around 11,000 miles). I was surprised. GM given up on trans fluid and Mobil1 now makes the fluid for the A8.

I didn't trust GM or Mobil1 for the new trans fluid after dealing with more than half the miles having issues. I wanted a true lifetime fluid (100K miles) Not a 36,002 mile warranty failing fluid.

[awrj2000]

http://allcarvideos.net/2017/07/19/c...no-dipstick-2/

Watch 09:30 to 10:30 in this video.

I still went Amsoil transmission fluid.

[Captain J]

Ok...So I just got a new left over 2017 Vert. It had 54 miles on it when I bought it. A week later, I've got 250 miles on it. It's had this shutter problem from day 2. I spoke with the service tech at the dealership and he claims to know nothing about it being a problem. To the OP, thanks for posting the Service Bulletin number. I've printed it out and will be bringing it to the dealership. Hopefully I didn't just buy a $37,000 PITA, POS!

[awrj2000]

Originally Posted by Captain J

Ok...So I just got a new left over 2017 Vert. It had 54 miles on it when I bought it. A week later, I've got 250 miles on it. It's had this shutter problem from day 2. I spoke with the service tech at the dealership and he claims to know nothing about it being a problem. To the OP, thanks for posting the Service Bulletin number. I've printed it out and will be bringing it to the dealership. Hopefully I didn't just buy a $37,000 PITA, POS!

I would at least give it 1500 mile break in.

The issue with shutter is like being on the freeway and veering right into the rumble strips. A less apparent shake of the car and steering wheel.

For the low miles in your car it may truly be a torque converter issue, but again let it break in and then get the flush to dump all that "loose" material from break in.