Does anyone else notice this about the A8?

[CptMcSaug]

I have almost 10k miles on my truck right now. 6.2/8 speed 4x4 Crew Cab. I was pulling a trailer yesterday empty might be 1000lbs. My truck would constantly lock and unlock varying 100 RPM about 65mph and you would feel a shudder. I do have 10ply ties but that shouldn't mean anything.

 

On the way to work today with no trailer I noticed the same thing. But no shudder this morning?

 

http://vid961.photobucket.com/albums/ae98/Trophydeer9/Mobile%20Uploads/20150918_155131.mp4

[CptMcSaug]

http://i961.photobucket.com/albums/ae98/Trophydeer9/Mobile%20Uploads/th_20150918_155131.mp4

[j-ten-ner]

I'd guess that the truck is switching between V8 and V4 mode.

 

so long

j-ten-ner

[KCXLT]

There is a recall about torque converter shudder. Its either 15389 or 15396. I think its just a re-program.

[SkiDooNick700]

I had the recall done a while ago. I noticed this whole driving on the hugh way doing around 70 or 75. I noticed the RPM Guage constantly moving up and down ever so slightly. This was with cruise on and off. Even with it on, other cars I've been in don't do this.

 

Another thing I noticed with this 8 speed, it is kind of clunky sometimes when it shifts after you let off the gas or give light throttle pressure.

 

Another thing too is that I've had a couple experiences where I've had to brake pretty hard. Well, when the trans is downshifting real fast to keep up with rapid deceleration, it actually lurked me forward, like the brakes gave out for a split second. Kind of a scary feeling. Anyone else experience this?

 

I mean overall, I feel, I'd say, 7 out of 10 on this 8spd. It just can be too clunky at times. I'm not sure if it's my driving habits or what. I'm generally pretty easy on the throttle rarely exceeding 2000 rpms.

[CptMcSaug]

There is a recall about torque converter shudder. Its either 15389 or 15396. I think its just a re-program.

I'm the one who started the thread telling people about it haha.

 

I might take it to the dealer

[Higgs Boson]

1st, the recalls/tsb/flashes don't cure the crappy shifting calibration in the A8.

 

2nd, I have completely cured the poor calibration by reprogramming the shift point and torque converter lock/unlock settings (I also gained 1 MPG by doing this).

 

3rd, almost all automatic transmissions have a small amount of converter slip (20-50 RPMs) at cruise, you only notice on the A8 because we are all hypersensitive to its characteristics right now.

 

4th, the rapid deceleration lurch at stop is horrible. i have lessened its frequency through tuning as stated above, but also altering the Rolling Idle settings and Driver Demand tables, but it is not gone. This is the only thing left to figure out at this point. My dealer thinks the drivetrain is getting bound up and releasing energy on the hard brake stops (not that hard, just not slow and soft). Can't fix that in a tune, they want to grease some stuff underneath to see what happens.

[iCryWheniGoPoop]

If its lurching forward on braking, at what I'm assuming is when you are almost completely to a stop, then there is a problem with the converter and or the TCM calibration related to the convertor.

 

There is a TSB out looking for noise in the converter (a whine I believe) and my service manager said they replace it if they hear the whine. They actually took mine for a test drive for this TSB to listen for it. I have yet to experience the lurching

 

 

 

 

Sent from Off Driller Side

[Higgs Boson]

it may be mechanical because my downshift 2-->1 is at 8 MPH and the converter is unlocked in first. this is why my local service manager is thinking its an issue on one end of the driveshaft.

[bboyce536]

Higgs, wanna tune my truck? Sounds like you've learned all about tuning these 8 speeds.

 

Mine surges after an upshift and the rpms vary while cruising all the time. Im all up to date as far as GM updates are cocerned too.

[Higgs Boson]

If you have HPTuners you can email me your tune and I will fix it up for you.

[CptMcSaug]

Wish I had hpt

[iCryWheniGoPoop]

it may be mechanical because my downshift 2-->1 is at 8 MPH and the converter is unlocked in first. this is why my local service manager is thinking its an issue on one end of the driveshaft.

When I think of lurching i am picturing it lunging/bucking as it approaches a complete stop due to engine trying to stay running as it is being held by rest of the drivetrain. (Like when your wife decides she wants do drive the car for the first time and forgets to push in the clutch as she comes to a stop)

Since the convertor is the coupler between engine/trans which should be disengaging in this situation (like u said 8mph + throttle angle) I can't see how anything else would cause this. If the convertor was disengaging like it should be the rest of drivetrain shouldn't really matter as it should be in a free coasting state and if there are other issues it would cause more of a dragging/binding issue (at least that's how I see it anyway)

 

Maybe I'm just misinterpreting what the lurching actually is since I haven't experienced it yet.

If I'm right on what you guys are calling lurching, I'd bet dinner on convertor related issues: clutches are hanging/binding, TCC solenoid is failing/sticking or there is a false intermittent signal/voltage bleed that is just enough to hold solenoid in its open state. Since it sounds like it is letting go eventually, I lean towards clutches hanging in the convertor and I'm thinking this new A8 is a multi disk now, but I could be mistaken.

 

I may go try some hard braking and see if I can duplicate this issue, how often would you guys say it happens.

 

Epiphany- I wonder if trans is just slow to shift from second on hard braking and throttle angle is reported to high for TCC release. If that's the case, I would try to raise TCC engage/release parameters to as high as possible and still operable on highway (or temporarily remove completely) and see if it helps.

 

 

 

 

 

 

 

Sent from Off Driller Side

[Higgs Boson]

remember the converter is unlocked in first at any speed, it will even happen if you keep it unlocked in second also.

 

the lurch is more like, "I think someone just rear-ended me!" Boom! Its very abrupt.

 

If you do a limo stop, like let off brake pressure as you approach stop, which I think is more normal, it can alleviate or eliminate the issue. if you happen to hold steady brake pressure all the way to 0 MPH it is more likely to bang. like it gets stopped and is all loaded up with pent up energy and releases it at 0.

[Higgs Boson]

Wish I had hpt

 

They still sell it. :-)