Slight hesitation when maintaining speed
Thread Starter
Instructor
Joined: Apr 2019
Posts: 239
Likes: 62
From: West Sacramento, CA
Slight hesitation when maintaining speed
I'm looking for input. I just acquired a 2018 last week and noticed when I had it on cruise control that the RPM would drop 100-200 about every two seconds. It is just like a yoyo effect. I took it off cruise and just maintained a steady speed and it still does it. So that ruled out cruise. The dealer said they test drove it and put on the meter and it is running okay. No misses, transmission is shifting okay, etc. When he said that, I'm thinking shifting? I said this does it when the speed is steady. I'm not believing that is normal behavior. I've tested this at neighborhood speeds of about 45 and highway speed of 65 and it happened under both circumstances. It is very unnerving. I can definitely feel the slow up and speed up through the car.
Thanks for any input. I'm supposed to pick it up tomorrow.
Bob
Thanks for any input. I'm supposed to pick it up tomorrow.
Bob
Last edited by MrClean21; Apr 17, 2019 at 09:27 PM.
Drifting
Joined: Sep 2017
Posts: 1,464
Likes: 771
From: Miami
C7 of Year Finalist (performance mods) 2019
Unfortunately, sounds like the A8 transmission shudder issue. Have the dealership perform the triple flush. And consider getting a Range device to eliminate AFM.
Last edited by DTOM; Apr 17, 2019 at 09:41 PM.
Thread Starter
Instructor
Joined: Apr 2019
Posts: 239
Likes: 62
From: West Sacramento, CA
Pro
Joined: Mar 2018
Posts: 677
Likes: 414
From: Pensacola, FL
A Range Device is a module that plugs into the OBDII port under the steering column and it will keep your car from shifting into V4 mode. Or you can put your car in Manual, using the paddle shifter's, and see if that cures the problem. By doing this your car will stay in V8 mode and not shift in and out of V4 mode. Good Luck
Thread Starter
Instructor
Joined: Apr 2019
Posts: 239
Likes: 62
From: West Sacramento, CA
If someone has a way of getting this post over to a better forum, please do.
A big thank you to DTOM and Akcajunz for your very informative replies. I texted my service adviser this morning asking him to look into the TCC Shudder issue. I have 17,000 miles on my car. I also sent him screen shots of sites and this link, which I found to be invaluable. Here are the highlights.
1) To ensure TCC shudder is diagnosed correctly, drive the vehicle on a smooth road with transmission sump temperature between 122°F (50°C) – 158°F (70°C). Constant throttle input on a smooth grade is needed.
2) A shudder condition may also be a chuggle, surge or vibration condition. Use GDS 2 or the CH-51450 PicoScope to confirm that the concern is TCC shudder and not a tire/wheel vibration or a driveline vibration, for example.
3) If TCC shudder is present, a vibration peak will appear within +/- 2 Hz of the frequency listed in Bulletin #18-NA-355. (there is a chart displayed for this section)
https://www.midenginecorvetteforum.c...rvice-bulletin
Fluid Exchange
The TCC shudder condition is related to moisture content in the transmission fluid. The current fluid tends to be hydroscopic, or absorbs moisture, which increases the chance of TCC shudder. There are three different fluid exchange procedures to follow, depending on vehicle application, so that an acceptable concentration of the new HP fluid is achieved in the transmission.
The new Mobil 1 Synthetic LV ATF HP transmission fluid is now available to U.S. dealerships through your local GM Oil Distributor. The new Mobil 1 Synthetic LV ATF HP transmission fluid is available in quart bottles (GM Part Number 19417577) and, for a limited time, in 55-gallon drums (GM Part Number 19417904) in most locations. Drum production ended in January 2019. The GM part numbers are not on the product.
The Mobil 1 Synthetic LV ATF HP fluid and the required tool kit will be available to all Canadian dealerships by the end of March 2019. GM Part Numbers for 0.946 liter bottles will be provided at that time.
TIP: Mobil 1 Synthetic LV ATF HP transmission fluid is required for all 8-speed transmission repairs regardless of the repair being completed.
Quart bottles, which can be identified by a new blue banner across the front of the bottle (Fig. 12), will be limited to 20 cases/120 quarts per dealer per week during the initial launch of the new product. The new bottles also feature the HP license number J-62120 on the back label.
A big thank you to DTOM and Akcajunz for your very informative replies. I texted my service adviser this morning asking him to look into the TCC Shudder issue. I have 17,000 miles on my car. I also sent him screen shots of sites and this link, which I found to be invaluable. Here are the highlights.
1) To ensure TCC shudder is diagnosed correctly, drive the vehicle on a smooth road with transmission sump temperature between 122°F (50°C) – 158°F (70°C). Constant throttle input on a smooth grade is needed.
2) A shudder condition may also be a chuggle, surge or vibration condition. Use GDS 2 or the CH-51450 PicoScope to confirm that the concern is TCC shudder and not a tire/wheel vibration or a driveline vibration, for example.
3) If TCC shudder is present, a vibration peak will appear within +/- 2 Hz of the frequency listed in Bulletin #18-NA-355. (there is a chart displayed for this section)
https://www.midenginecorvetteforum.c...rvice-bulletin
Fluid Exchange
The TCC shudder condition is related to moisture content in the transmission fluid. The current fluid tends to be hydroscopic, or absorbs moisture, which increases the chance of TCC shudder. There are three different fluid exchange procedures to follow, depending on vehicle application, so that an acceptable concentration of the new HP fluid is achieved in the transmission.
The new Mobil 1 Synthetic LV ATF HP transmission fluid is now available to U.S. dealerships through your local GM Oil Distributor. The new Mobil 1 Synthetic LV ATF HP transmission fluid is available in quart bottles (GM Part Number 19417577) and, for a limited time, in 55-gallon drums (GM Part Number 19417904) in most locations. Drum production ended in January 2019. The GM part numbers are not on the product.
The Mobil 1 Synthetic LV ATF HP fluid and the required tool kit will be available to all Canadian dealerships by the end of March 2019. GM Part Numbers for 0.946 liter bottles will be provided at that time.
TIP: Mobil 1 Synthetic LV ATF HP transmission fluid is required for all 8-speed transmission repairs regardless of the repair being completed.
Quart bottles, which can be identified by a new blue banner across the front of the bottle (Fig. 12), will be limited to 20 cases/120 quarts per dealer per week during the initial launch of the new product. The new bottles also feature the HP license number J-62120 on the back label.
Drifting
Joined: Sep 2017
Posts: 1,464
Likes: 771
From: Miami
C7 of Year Finalist (performance mods) 2019
Here is a the link to the TSB and additional input from forum members. The last thing you want to end up with a torque converter replacement caused by the AFM kicking in and out of V4/V8 mode. The Range device prevents this - a must have for all A8's
https://www.corvetteforum.com/forums...8-flush-2.html
A8 failure tracking thread:
https://www.corvetteforum.com/forums...-tracking.html
I just modded my Z06 and had it tuned out. It's for sale here:
https://www.corvetteforum.com/forums...-disabler.html
https://www.corvetteforum.com/forums...8-flush-2.html
A8 failure tracking thread:
https://www.corvetteforum.com/forums...-tracking.html
I just modded my Z06 and had it tuned out. It's for sale here:
https://www.corvetteforum.com/forums...-disabler.html
Last edited by DTOM; Apr 18, 2019 at 12:03 PM.
Pro
Joined: Mar 2018
Posts: 677
Likes: 414
From: Pensacola, FL
Here is a the link to the TSB and additional input from forum members. The last thing you want to end up with a torque converter replacement caused by the AFM kicking in and out of V4/V8 mode. The Range device prevents this - a must have for all A8's
https://www.corvetteforum.com/forums...8-flush-2.html
A8 failure tracking thread:
https://www.corvetteforum.com/forums...-tracking.html
I just modded my Z06 and had it tuned out. It's for sale here:
https://www.corvetteforum.com/forums...-disabler.html
https://www.corvetteforum.com/forums...8-flush-2.html
A8 failure tracking thread:
https://www.corvetteforum.com/forums...-tracking.html
I just modded my Z06 and had it tuned out. It's for sale here:
https://www.corvetteforum.com/forums...-disabler.html
This is the reason I have become comfortable driving in "M" and using the paddle shifters. And from what I've experienced with MPG's...there is a very negligible difference in the MPG's from V4 to V8. I still see 25+ MPG's driving 80 on the interstate!
Thread Starter
Instructor
Joined: Apr 2019
Posts: 239
Likes: 62
From: West Sacramento, CA
Had I known about the A8 shudder issue when I was looking for my Vette I would have looked for the M7 instead. I just didn't want to deal with the clutch in California stop and go traffic. Yuk!
Bob
Bob
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Supporting Vendor
Joined: Dec 2018
Posts: 1,741
Likes: 820
From: South Alabama
MrClean, the shudder manifest mainly with a feeling as if driving over rumble strips. I had it on my 2015 A8. Did you get any of that? Check this thread and see if you also have any of the symptoms on post #1.
https://www.corvetteforum.com/forums...post1598646214
Having the triple flush done can't hurt, but if it doesn't solve the problem and they keep telling you it is normal, please give us a chance. The hesitation may very well be related to the throttle.
https://www.corvetteforum.com/forums...post1598646214
Having the triple flush done can't hurt, but if it doesn't solve the problem and they keep telling you it is normal, please give us a chance. The hesitation may very well be related to the throttle.
__________________
Soler Performance LLC
support@solerengineering.com
www.solerengineering.com
(251) 468-9786
Soler Performance LLC
support@solerengineering.com
www.solerengineering.com
(251) 468-9786
Thread Starter
Instructor
Joined: Apr 2019
Posts: 239
Likes: 62
From: West Sacramento, CA
MrClean, the shudder manifest mainly with a feeling as if driving over rumble strips. I had it on my 2015 A8. Did you get any of that? Check this thread and see if you also have any of the symptoms on post #1.
https://www.corvetteforum.com/forums...post1598646214
Having the triple flush done can't hurt, but if it doesn't solve the problem and they keep telling you it is normal, please give us a chance. The hesitation may very well be related to the throttle.
https://www.corvetteforum.com/forums...post1598646214
Having the triple flush done can't hurt, but if it doesn't solve the problem and they keep telling you it is normal, please give us a chance. The hesitation may very well be related to the throttle.
