A8 Issues
Melting Slicks
Joined: May 2012
Posts: 2,903
Likes: 315
From: Cedar Falls Iowa
Yes, and also a torque converter (transmission) was what was required because of the stupid AFM. The TC helps to dissipate much of that vibration that is caused from the transition from V8 to V4 and back.
I'm no expert and still learning, myself, but i believe the TC slip is computer controlled to "micro" slip when the AFM transition is made in order to absorb some of the vibrations. A DCT is not able to do this, thus the requirement for a classic torque converter auto.
This is a great transmission, all issues aside. It shifts in auto faster than a dual clutch, even though technically speaking there are alot of similarities between a DCT and this 8L90 that it shifting as fast, or faster, shouldn't be a surprise to anyone.
I'm no expert and still learning, myself, but i believe the TC slip is computer controlled to "micro" slip when the AFM transition is made in order to absorb some of the vibrations. A DCT is not able to do this, thus the requirement for a classic torque converter auto.
This is a great transmission, all issues aside. It shifts in auto faster than a dual clutch, even though technically speaking there are alot of similarities between a DCT and this 8L90 that it shifting as fast, or faster, shouldn't be a surprise to anyone.
Last edited by DAFFYDRUNK; Jan 21, 2016 at 05:23 PM. Reason: added more blahblahblah...
Drifting
Joined: May 2015
Posts: 1,412
Likes: 140
Burning Brakes
Joined: Oct 2010
Posts: 833
Likes: 240
The newer part # is 24274892. The earlier part# is 24273222.
My 2016 pulls up the newer part # but I suspect the newer part# will pull up for 2015 as well as it has replaced the earlier discountinued part#.
My 2016 pulls up the newer part # but I suspect the newer part# will pull up for 2015 as well as it has replaced the earlier discountinued part#.
Intermediate
Joined: Dec 2015
Posts: 25
Likes: 3
They claim it shifts faster than a dual clutch but my money is on Porsche PDK being faster in the real world. Not dissing on the A8, just saying I've driven both and at least the Porsche PDK is more responsive regardless of what GM claims. Also the M7 has noting to dampen the effect of the V4 transitions and it's still not bad. A little more noticeable than the A8 though.
Drifting
Joined: Nov 2014
Posts: 1,782
Likes: 106
From: Salado TX
I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though.
Burning Brakes
Joined: Jul 2015
Posts: 920
Likes: 87
Burning Brakes
Joined: Oct 2010
Posts: 833
Likes: 240
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Safety Car
Joined: Sep 2001
Posts: 4,495
Likes: 1,263
From: Jacksonville FL
I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though.
Chevrolet advertises in the showroom that the switch from V8 to V4 is seamless. Don't think so on my car.
Intermediate
Joined: Apr 2008
Posts: 36
Likes: 0
From: Salado TX
2016 A8 1st to 2nd harsh shift
My 2016 Z51 A8 built August 19, 2015 has very harsh shift when first shifting when driven after start up. Subsequent shifts are ok but first shift is always harsh. My guess is that the torque converter leaks down when the engine is off and the fluid has to repressure before shifts are normal. The 2016 has the auxiliary cooler up front under the front clip and that adds additional fluid that must repressure.
Le Mans Master
Joined: Sep 2012
Posts: 7,146
Likes: 1,940
From: Hagerstown MD
St. Jude Donor '15-'16,'18
My 2016 Z51 A8 built August 19, 2015 has very harsh shift when first shifting when driven after start up. Subsequent shifts are ok but first shift is always harsh. My guess is that the torque converter leaks down when the engine is off and the fluid has to repressure before shifts are normal. The 2016 has the auxiliary cooler up front under the front clip and that adds additional fluid that must repressure.
Le Mans Master
Joined: Nov 2015
Posts: 7,382
Likes: 3,501
From: Lake Havasu City Arizona
Mine has a build date of Oct 2015 and I don't experience any of these harsh shifting issues. Cold or warmed up.
I don't experience this either:
"I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though."
I don't experience this either:
"I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though."
Last edited by joemessman; Jan 23, 2016 at 05:38 PM.
Drifting
Joined: May 2015
Posts: 1,412
Likes: 140
Mine has a build date of Oct 2015 and I don't experience any of these harsh shifting issues. Cold or warmed up.
I don't experience this either:
"I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though."
I don't experience this either:
"I tried this yesterday afternoon. I have to drive across the top of a dam to get home so I know there is a mile or so of perfectly level road. I set the cruise on 65 and watched the tachometer. It moved rhythmically between 1400 and 1600 RPM. If it had been a sine wave I'd say it has a period of about 4 seconds--two up and two down. I didn't feel any shudder in the wheel though."
Safety Car
Joined: Sep 2001
Posts: 4,495
Likes: 1,263
From: Jacksonville FL
It has been reported on this forum that the new A8 transmission part # 24274892 was placed in the C-7s starting in October, 2015.
Last edited by Red C8 of Jax; Jan 23, 2016 at 07:18 PM.
Racer
Joined: Nov 2015
Posts: 451
Likes: 181
From: Stuart FL
Burning Brakes
Joined: Jul 2015
Posts: 920
Likes: 87
but they most likely will not ....so the owners such as myself ...will be screwed because we put so few miles on the car ...and the real issue will not arise until out of warranty ..
my C7 is stored for the winter less that 400 miles..
it did shift hard 1st to 2nd ... when first starting ..even if i let it warm up ..