[modru2004]

Originally Posted by T32803

The Shudder bulletin describes the condition as this:

• A shake and/or shudder during light throttle acceleration between 40 and 128 km/h (25 and
80 mph) steady state driving when transmission is not actively shifting gears.
• A shudder feeling that may be described as driving over rumble strips or rough pavement.
• Shudder feeling is evident in both Drive and M7 MY15-16 & L7 MY17 mode.

This is exactly what I hear and feel. Especially the sound and vibration as if I
was "driving over rumble strips or rough pavement".

It only occurs (that I notice) during light throttle acceleration between 25 and 50 mph
usually after I have been cruising in traffic then try to add a little bit of speed. I virtually
never see the green V4 light come on because I am always driving in the city.

What is it about my description that makes you so sure that it is AFM and not shudder?

If I am not seeing the green V4 light come on then how can it be AFM?

And if AFM can be a problem even when the V6 light is always on, then how the heck can
it last for long periods of time unless I intervene and force it with a manual downshift
or flooring it ?

i gave you some steps to help troubleshoot and narrow down the issue but you seem to have your mind made up. if you are so convinced that you have the A8 torque converter shudder from the TSB why are you even on here asking? take it to the dealer and have it fixed.

[chevyboy01438]

This is what they are calling it. They said if there was an issue it would throw a code. Because there is no code, they won't do anything

[modru2004]

Originally Posted by chevyboy01438

This is what they are calling it. They said if there was an issue it would throw a code. Because there is no code, they won't do anything

if the 1-2 shift thing is your issue its pretty common and considered normal. in fact its common on other vehicles as well. the 8 speed rams do similar things as well and its been discussed to death. basic tldr from the ram discussions is its standard operating procedure.

[chevyboy01438]

It does this and I told them this wasn't my concern. It is between 5, 6, and 7th loosing power before shifting. They said if there was an issue it would throw a code and because there is no code, they won't do anything. i'm going to print this other bulletin and try a different dealership

[KMPrenger]

What a joke. You clearly tell them its something else, and they point you at this bulletin and tell you nothing they can (or will) do. I honestly don't understand how they couldn't help you if you were to show them the correct bulletin and tell them this is what you are experiencing.

Also, I'm pretty sure almost nobody gets a code from the shudder...unless maybe they've gone so long that the TC is completely toast.

[JT58]

I did not get a code from the shudder. The dealer was very good in acknowledging the issue and even explained the steps- flush first, drive and see if the issue goes away, second step is to replace the torque converter. But mine is a 2017. They said the shudder issue is common in all the A8's- Camaros, Corvettes, Silverados and Colorados. I would think that GM would have resolved the issue for the 2018's though.........

[crosive]

Originally Posted by JT58

I did not get a code from the shudder. The dealer was very good in acknowledging the issue and even explained the steps- flush first, drive and see if the issue goes away, second step is to replace the torque converter. But mine is a 2017. They said the shudder issue is common in all the A8's- Camaros, Corvettes, Silverados and Colorados. I would think that GM would have resolved the issue for the 2018's though.........

This is what happened to me. I replicated the issue a while back, got the triple flush. It came back, I replicated the issue and the shop foreman acknowledged it before we even hit the first redlight (directly in front of the dealership). I was told by him it meant a new torque converter, but when I picked it up, they said TAC told them to flush it again.

[T32803]

Originally Posted by modru2004

i gave you some steps to help troubleshoot and narrow down the issue but you seem to have your mind made up. if you are so convinced that you have the A8 torque converter shudder from the TSB why are you even on here asking? take it to the dealer and have it fixed.

I guess I was sharing what I experienced and was asking you to explain why you thought it was being caused by AFM when the green V4 light never came on. It's a frustrating situation for a new car buyer and I feel terrible for buying this car. The car looks great but driving in city traffic sucks because the A8 transmission does an atrocious job of handling light acceleration between 25-50mph. The A8 should downshift more aggressively when needed. The A8 does not perform normally as compared to any of my previous automatic transmission cars. No offense to you, I just wanted to know your reasoning in case there was something I was missing.

[modru2004]

Originally Posted by T32803

I guess I was sharing what I experienced and was asking you to explain why you thought it was being caused by AFM when the green V4 light never came on. It's a frustrating situation for a new car buyer and I feel terrible for buying this car. The car looks great but driving in city traffic sucks because the A8 transmission does an atrocious job of handling light acceleration between 25-50mph. The A8 should downshift more aggressively when needed. The A8 does not perform normally as compared to any of my previous automatic transmission cars. No offense to you, I just wanted to know your reasoning in case there was something I was missing.

well my reasoning is the problem you described sounds exactly like a lugging engine. as anyone with manual experience can tell you trying to accelerate in too high of a gear will cause similar symptoms. my 8 speed hemi ram with afm used to behave similarly around 40mph it would pick a super high gear and the AFM would kick on turning off 4 cylinders and anytime you tried to accelerate it would lugg and vibrate and shake a bit. it refused to downshift or turn off the AFM unless you got a bit more aggressive with the throttle.

if you have the TC issue that everyone talks about it should be happening in other gears as well even on the highway at higher speeds. if you can reliably replicate your symptoms it will make it easier to tell the dealer exactly whats wrong and how they need to replicate the issue so you can get it fixed.

[T32803]

I'm going to go out on a limb to postulate "how" I think the programmed slip
tables are causing this:

You accelerate to 30 from a stop then ease up on the gas to maintain 30.
The A8 floats up to a high gear like 7 when it feels no load.

5 seconds later you want to slowly speed up to 40.
(The car says "D" so you don't know the gear it is in)

The A8 should instantly downshift from 7 as soon as I apply gas at 30.
(because the load of trying to accelerate from 30 in gear 7 is too high)

But it seems like it remains in that high gear and labors, shudders, and
transmission slips as it tries to maintain that high gear.

I am thinking that the programmed slip tables allow the transmission to
slip when the A8 has you in a high gear (like 7) and you try to gently
accelerate from a cruising 30mph.

This programmed slip may be just enough prevent the A8 from triggering
a downshift from 7 to the much lower gear needed to provide smooth
acceleration.

This explains for me why this goes away as soon as hit the manual
downshift paddle. (Or you can floor the gas to create a huge load
to force the downshift)

So I am betting that eliminating the slip tables would allow the A8 to
downshift more aggressively and avoid the shudder condition completely.

My previous automatic cars never labored like this. They stayed with
whatever gear was right for the speed and downshifted aggressively
whenever the transmission felt a load. The A8 should work this way.

[modru2004]

Originally Posted by T32803

I'm going to go out on a limb to postulate "how" I think the programmed slip
tables are causing this:

You accelerate to 30 from a stop then ease up on the gas to maintain 30.
The A8 floats up to a high gear like 7 when it feels no load.

5 seconds later you want to slowly speed up to 40.
(The car says "D" so you don't know the gear it is in)

The A8 should instantly downshift from 7 as soon as I apply gas at 30.
(because the load of trying to accelerate from 30 in gear 7 is too high)

But it seems like it remains in that high gear and labors, shudders, and
transmission slips as it tries to maintain that high gear.

I am thinking that the programmed slip tables allow the transmission to
slip when the A8 has you in a high gear (like 7) and you try to gently
accelerate from a cruising 30mph.

This programmed slip may be just enough prevent the A8 from triggering
a downshift from 7 to the much lower gear needed to provide smooth
acceleration.

This explains for me why this goes away as soon as hit the manual
downshift paddle. (Or you can floor the gas to create a huge load
to force the downshift)

So I am betting that eliminating the slip tables would allow the A8 to
downshift more aggressively and avoid the shudder condition completely.

My previous automatic cars never labored like this. They stayed with
whatever gear was right for the speed and downshifted aggressively
whenever the transmission felt a load. The A8 should work this way.

if you slap the shifter over to M mode when you get the issue it will show you what gear you are currently in.

[crosive]

Originally Posted by T32803

I'm going to go out on a limb to postulate "how" I think the programmed slip
tables are causing this:

You accelerate to 30 from a stop then ease up on the gas to maintain 30.
The A8 floats up to a high gear like 7 when it feels no load.

5 seconds later you want to slowly speed up to 40.
(The car says "D" so you don't know the gear it is in)

The A8 should instantly downshift from 7 as soon as I apply gas at 30.
(because the load of trying to accelerate from 30 in gear 7 is too high)

But it seems like it remains in that high gear and labors, shudders, and
transmission slips as it tries to maintain that high gear.

I am thinking that the programmed slip tables allow the transmission to
slip when the A8 has you in a high gear (like 7) and you try to gently
accelerate from a cruising 30mph.

This programmed slip may be just enough prevent the A8 from triggering
a downshift from 7 to the much lower gear needed to provide smooth
acceleration.

This explains for me why this goes away as soon as hit the manual
downshift paddle. (Or you can floor the gas to create a huge load
to force the downshift)

So I am betting that eliminating the slip tables would allow the A8 to
downshift more aggressively and avoid the shudder condition completely.

My previous automatic cars never labored like this. They stayed with
whatever gear was right for the speed and downshifted aggressively
whenever the transmission felt a load. The A8 should work this way.

my understanding is that, and I'll use freeway speeds for example, around 60-80, the torque converter is locked, and you're in 7-8 (doesn't matter, both exhibit it, or did for me), the low pressure pump is not enough to hold converter locked. The slip tables allow up to 15 revolutions. since the low pressure pump isn't enough to "hold", it slips, hits the 15 revolution limit, the high pressure pump kicks in, locking the converter, thus the vibration occurs. In my case, this happened every second or so. So much that I could even see the rpm needle move when it happened.

when you zero out the slip tables, I believe it locks the high pressure pump on all the time, not allowing the converter to slip. It's a possibility that improper fluid, such as mentioned by Al, accentuated this, and possibly even accelerated the failure of the paper friction surface of the torque converter clutch plate. Also from my understanding, once that happens, everything afterwards, other than replacement, is just a bandaid.

If anyone has better info, or wants to correct me, feel free to.

[T32803]

Originally Posted by modru2004

it refused to downshift or turn off the AFM unless you got a bit more aggressive with the throttle.

if you have the TC issue that everyone talks about it should be happening in other gears as well even on the highway at higher speeds. if you can reliably replicate your symptoms it will make it easier to tell the dealer exactly whats wrong and how they need to replicate the issue so you can get it fixed.

"Refusing to downshift" as you mentioned when trying to accelerate
is a defect in the transmission design. It's basically telling the consumer
you can't drive your car gently in traffic but instead you need to go heavy
on the gas to avoid having the car shake, rumble, and make bad noises.
It's ludicrous to accept this as ok when other cars aren't like this.

In city traffic you want to drive easy to avoid getting into an accident.
The problem is that the A8 is not downshifting when it should be.

I thought AFM was only about turning off 2/4 cylinders to save fuel.
If AFM is also causing the A8 to put the car in gear 6 or 7 during
low cruising rates of speed like 30 mph I could buy that. But its an
absolute defect if the A8 cannot downshift immediately when you
accelerate.

I will try the tests you wrote earlier see what I notice. Thanks..

[T32803]

Originally Posted by crosive

my understanding is that, and I'll use freeway speeds for example, around 60-80, the torque converter is locked, and you're in 7-8 (doesn't matter, both exhibit it, or did for me), the low pressure pump is not enough to hold converter locked. The slip tables allow up to 15 revolutions. since the low pressure pump isn't enough to "hold", it slips, hits the 15 revolution limit, the high pressure pump kicks in, locking the converter, thus the vibration occurs. In my case, this happened every second or so. So much that I could even see the rpm needle move when it happened.

when you zero out the slip tables, I believe it locks the high pressure pump on all the time, not allowing the converter to slip. It's a possibility that improper fluid, such as mentioned by Al, accentuated this, and possibly even accelerated the failure of the paper friction surface of the torque converter clutch plate. Also from my understanding, once that happens, everything afterwards, other than replacement, is just a bandaid.

If anyone has better info, or wants to correct me, feel free to.

This sounds much better than what I came up with. I was trying to
postulate why the hell the A8 isn't downshifting immediately to avoid
this condition because in my driving I constantly have hit the downshift
paddle twice to pull the car out of the nasty funk that it gets in.

The lugging that modru2004 describes happens often for me. This is the
car laboring and bogging down. I can reproduce this every day.

The single shuddering event I had encountered last weekend was on a
different scale and included shaking and a much deeper and louder moan
like when a garbage disposal gets jammed and can't spin. It's definitely
a "this is bad" moment. I'm probably not explaining it well but it's a far more
pronounced event and feels like the bogging down event plus more.

crosive:
I am just wondering if you thought the pump pressure and slip tables have
anything to do with the A8 not downshifting when it should? I mention the
A8 not downshifting to a lower gear when presented a load when trying to
accelerate gradually from 30 in a high gear like 7. Is any of this related?