I have closely followed all the A8 TC problem threads. Picked up my car 12/10/15 at MacMulkin with a build date of 9/15 on the door sticker. I initially thought I may be having some of the often quoted problems early on and had a reflash done at about 1,500 miles. That seemed to nearly eliminate most of the issues, mostly a 100-200 rpm fluctuation when cruising at a steady speed (V4). I decided the TC was working as designed and have been pretty happy with its performance since. Never noticed any shuttering. The V8-V4-V8 transition is seamless and the only issue is the delayed engagement first thing in the morning which I understand is another issue and I can live with that.

Now at 11,000 miles I have begun to experiment with driving in 'M' a lot and notice I am often getting a 50 rpm or so fluctuation when cruising with any change plus or minus on the accelerator. This naturally is in V8 mode where before it was pretty rock steady once the TC locked.

Also, I have also begun running the NPP in Track mode all the time. When puttering around town at light throttle, I notice what I can best describe as a "phantom" shift. I hear it more than feel it at about 40 mph or so, usually in 4th, sometimes 5th gear. It sounds like a drop in rpm but I have yet to be able to catch it on the tach (the car has PDR, do you think that would record it?). My suspicion is leaning toward an rpm drop at TC lockup and am wondering if this is normal and if others are experiencing it.

My local dealer has not had much if any experience with TC replacements, at least not a year ago when my car was reflashed. Is there any specific test I can ask them to perform to lead them to a diagnosis? I have read some info regarding TCC slip tests but my Torque app does not register that on my Android with this car.

What is the forum consensus? Are these two issues normal or should I have the dealer look into them, and if so what specifically should I ask them to test for an objective determination of proper operation?

 

Maybe you're just overthinking the whole situation my friend. A 50 rpm change is very hard to pin point, especially with the converter lock up in nearly every gear. And, as the "puttering around" there are so many variables a tranny goes through. You may even be experiencing the converter locking/unlocking when going easy on the gas.

I can't say my A8 does or doesn't do these things. I don't pay that much attention to it as long as it changes gears correctly. Good luck, I hope there's nothing wrong with yours.

 

At 40, it's probably the closing of the AFM valves, or may be going into V4 mode? Watch the gauge that shows the V4 status.

 

Thanks, you're probably right and I am over thinking it. The car drives and shifts great and I'm loving the A8 and really don't have any complaints with the tranny (coming from 13 years M6 experience and swearing I would never own another automatic Corvette). I admit to being a nervous nellie at first, then accepting that I don't have the problems others have experienced. I just started noticing these nuances recently after changing my modus operandi for daily driving.

 

Not the AFM valve or going into V4. I'm talking about driving in manual mode where the car stays in V8 all the time.

 

Good luck and hope your problems are solved and you keep enjoying your beautiful C7!

 

The phantom shift is likely the torque converter locking up as it is supposed to.

Here's a video of mine...fast forward to around 2:50 and watch until 3:20. Mine sounds like it is locking up around 3:15 in the video. Is this what yours is doing?

 

I do understand. I was hesitant at first to buy a C7 with the A8. So much so I looked hard for a pre owned '14 with the A6. But the prices of used were just to close to new, so I just shrugged it off, and bought one with the A8. So far, so good.

 

Thanks, it's a little hard to tell from the audio but that seems pretty much like what I am experiencing. Those headers really make a difference in the sound to my stock NPP though - I like it.

I had headers on my M6 '01 and really liked them but think I'll keep the C7 stock. The wife likes it quieter on trips and the tire noise is enough, even for me, and the NPP's in Track are pretty good for when we're not traveling. It's just not the same sound with an auto as with a manual though. Do you have any other mods that get that crisp gear change sound on your car?

 

Thanks for the compliments on the headers. The car is not nearly that loud on the inside. I had an external microphone taped to the back of the car, just below the spoiler so it was capturing the exhaust note right out of the tail pipes. Sound in the car, is really not a whole lot louder than the stock NPP, if I'm just easing it along. If I put my foot into the throttle it can get pretty loud in track mode. If you put it in stealth mode it is still very quiet. The sound level in stealth with the headers is pretty close to being in between stealth and track on on a stock system. I love the flexibility of this setup with being able to be loud or quiet when I want it to.

I have no other performance mods (I haven't even tuned it yet). The crisp shift is all in the timing of the shift. I am paddle shifting the car as if it was a manual. So I'm revving it out and then letting off the gas right after I hit the paddle so you can hear the RPM drop. Just takes a little practice on the timing, but anyone can do it. I used to be able to make the same crisp shifts with the stock exhaust system too. Just got to put it in manual mode and experiment a little with the timing and you'll be able to do it.