txapezl1

All clear over here so far. 16 model w/a Dec 15 build date. Of course, I only have 300 miles. haha. Just saying.

Red C8 of Jax

The tranny has to be removed. The dealer said the labor charge is the same replacing the TC or the entire tranny.

Mr. Jones

[QUOTE=iclick;1591480806]Do you or anyone else know what's involved in replacing a TC? I presume it dictates a tranny removal, so how invasive is that? In a C2 and most other RWD cars of that era it was quite easy, but I would bet it isn't in the C7.

Should be similar to C5 and C6 vettes. same setup since 1997

iclick

As an update to my reply #151 above, I followed the same route as I did yesterday but noticed no shuddering at all, and tach oscillation was much less prominent with a total range of perhaps 50rpm. It was more like 100 rpm yesterday, and ambient temps were about the same. Called SM at nearby dealership as I said I would but got voicemail and have not heard back from him. Friday is probably a bad day.

What's more, I got an On-Star report today that said I had issues with the Engine and Transmission System (see attached). I plugged in my code reader which said that no trouble codes were stored in the ECU, but a diagnostic test resulted in the following:

MID $41 TID: $94
O2 Heater Monitor Bank 1, Sensor 1
Min 26816
Max 40920
Current 65520

MID $30 TID: $b3
(no description)
Min 26928
Max 12289
Curr 65520

These don't look like A8 issues but I thought I would report them anyway.

Maxie2U

The report lists 9 different problem alerts (2 others don't apply to a C7), so its more than the Engine and Transmission Systems, no?

iclick

That's what I thought based on first glance, but since they include 4WD and hybrid alerts I assume that's just a list of everything included in that section of the diagnostics. They say to "Push your blue OnStar button and request an On-Demand Diagnostics check." When I do that it tells me I'm on a "limited plan" (not subscribing) and gives no diagnostic options.

Whatever is wrong it isn't throwing any codes or CELs and the car runs flawlessly, since the weirdness described yesterday anyway. Will probably go to the nearest competent dealer ASAP for a scan and a talk with the SM who didn't call me back today. I called late in the day so I'll cut him some slack and try again on Monday.

iclick

I was mostly wondering about the torque tube. Does it need to be re-aligned, and if so what's involved in that? My concern is whether a typical dealer tech can get it back up to original specs.

Orange Z06 Girl

They quoted 6 grand on ours when they were trying to get us to pay.

Orange Z06 Girl

I was told by a tech that he has had to replace engines because of screwed up transmission repairs. He told us to be sure they checked the crank end play. Of course our dealer couldn't say what ours was but said they checked it. I was kind of bothered when he said his guy has a "better way" of mating it all back up than gm recommends. I'm nervous about it but I've launched it hard and no issues. The tech said listen for a growl coming from motor area. Said it may even take 5000 miles to show up.

AED

I have a 2015 Z51 A8 and at 6k miles it started shuddering when driving (it could pretty much happen at any speed but was worse at low (30 mph) speeds and gentle driving). At first I was in denial then I thought it must be misfiring slightly (seemed like the most likely thing) and took it to the dealer. They said it wasn't misfiring and what it was doing was "in tolerance" so nothing for them to do... Well a $70k car shouldn't shudder like that when driving down the road.
After a while I realized that if I put it in Manual mode it quit instantly and if I put it back in Automatic mode the shuddering restarted. So for a while I drove it in Manual. I also realized that in Auto mode it was dropping into V4 and in Manual mode it was always in V8. It occurred to me it may be the AFM - felt like the small hiccup you get when it goes from V4 to V8 upon acceleration just that it was doing it over and over again.
I researched devices that prevent the car from going into AFM (V4) mode - several people complained that their GM cars were going V4-V8-V4-V8-V4-V8... all the time while they were driving and it seemed like this is what mine was doing too.
So for $199 I bought a device that plugs into the OBD2 port and disables the AFM. IT CURED THE PROBLEM INSTANTLY!
It does not reflash anything so no warranty issues - unplug it and the problem reappears. Doesn't mean to sat I don't have a Torque Converter issue but the only symptoms I had were the unpleasant shuddering while driving gently.
The bonus side effect of this device is that there is no unpleasant hiccup as it comes out of V4 when you get into the accelerator - it's always ready to go! Can't say I have noticed any real increase in fuel consumption by not being in V4 mode.

JoesC5

[QUOTE=Mr. Jones;1591484482]Powerglide transmission in a C2 cannot be removed without pulling the engine. Not that simple. Transmission can not be removed by itself as the rear crossmember is not removable.

Mr. Jones

[QUOTE=JoesC5;1591493248]understood but in a c5 and c6 the diff and trans can be pulled without removing the engine.

Lanbo

I think I have the same problem. When my engine is "cold" and I shift into drive, there is a delay of about 1-2 full seconds before it actually shifts into drive. If I stay on the brake during that whole time, the whole car violently shakes once when it actually shifts to first gear. It's less noticeable if you let off the brake before it shifts since it can actually go forward like it wants to. It only happens when shifting into drive, reverse has no hiccups. It's more noticeable the colder the engine. While it is more noticeable when it's cold outside, it still happens in 80 degree weather if I don't let it warm up. It seems to be that if the engine is warmed up enough that the tachometer doesn't have the extra yellow warning tics, then it doesn't happen. For example, this morning it was very violent. It was parked in my garage but I only let it run for about 5 minutes since I was running late for work. Temp outside was about 50. I left for lunch two hours after getting to work (I eat early since I don't eat breakfast ) and I let it run for about 5 minutes but since it was almost 80 outside and only sitting for 2 hours it was already warmed up. Didn't do it at lunch. Been going on for a few months now. Got about 7,000 miles.

I have a procharger installed so I've been reluctant to take it to the dealer. Not because I'm worried about the warranty, but because I don't want them to screw anything up.

EDIT: Also, I should note that since I have the procharger installed, the AFM is disabled (it can't go into V4 mode at any time). It's possible that my car could exhibit the same problem others have mentioned while driving but if it is indeed fixed by disabling the AFM then I wouldn't know if my car has that problem.

Red C8 of Jax

Next time you are on a straight level road, set your cruise control and see if your RPM's move up and down a little for as long as you are in cruise control. I think it will do this even if you are in V8. One of the signs of torque converter failure.

Maxie2U

If you want answers about the A8 transmission and torque converter be sure to cast your vote for this week's "ask Tadge" poll question, A8 Transmission/Torque Converter (full question to Tadge can be read in post#6, link below).

Voting ends February 21st.

https://www.corvetteforum.com/forums...ry-2016-a.html

Lanbo

Checked it out in a few spots yesterday and as far as I can tell rpms stay constant. On flat surfaces while on cruise control, I can't notice the line move a single bit. I also recorded it all in the PDR since I knew I couldn't stare at the tach the whole time. That didn't show any movements either.

Red C8 of Jax

Maybe you just need a transmission flush and filter. I also have read about a re-learn procedure. It seems like most of the folks with torque converter replacements, including myself, had the RPM's moving up and down at constant speed and after the torque converter swap the RPM's did not move.

iclick

At least one person who did the fluid/filter change reported that his tach quit oscillating.

iclick

At least one person who did the fluid/filter change reported that his tach quit oscillating and the shudder disappeared.

RODXL1200

There is a fix for this. Ask your dealer when you go in to pull it up. Mine shifted really hard at first shift at start up. After the simple program fix it shifts completely smooth every time.