I continue to experience random issues with the A6 transmission in my C6 GS (see signature). I have sometimes experienced issues with the 2-3 shift hesitating. Also, I had issues where after the burnout the trans went into 'limp mode"- staying in a higher gear and not downshifting back to 1st. At the suggestion from various sources a shift into neutral after the burnout and back to drive before staging seemed to be a fix.

Last weekend, after the first burnout the car would not move in any shifter position- it seemed like the transmission was in both drive and reverse as if it had a transbrake (which it does not of course.) After rowing through all the shifter positions a number of times it returned to normal and I was able to stage and make the run. I made three later runs with no problem.

Does this appear to be issues with the Transmission Control Module (TCM)? I live in the Orlando FL. area and the transmission was built by a company in Texas. I would like to avoid having my local tuner shop pull the transmission and send it back to Texas to be checked out. Is it reasonable to ask that my local tuner to collaborate with the transmission builder to remotely check out the transmission tuning / Transmission Control Module?

I must admit I do not understand which A6 parameters are typically set by the transmission builder vs. the car tuner using the dyno and if the TCM settings can be accessed via the local tuner’s HP software on the dyno vs directly to the TCM.

Thanks in advance for assistance.

 

Man, you’ve not had any luck with those 6L80s, huh?
It seems unlikely that’s it’s a tuning issue if it’s intermittent like that. It might be the TCM acting up. Did it throw any DTCs?
First thing I would check would be the TCM harness plug that goes into the trans to make sure it’s locked. If it is, unlock it and pull it off to see if there’s any dirt or obvious damage to either side of the plug.
If that’s not the problem, you could get a new TCM and install it yourself, but you’ll need a dealer (or someone with a Tech 2 programmer) to reprogram the new TCM with your VIN and then have your TCM tune reloaded into it. You can’t program the VIN with HP Tuners.
But, your existing TCM tune can be read and copied and then reprogrammed into the new TCM with HP Tuners once the VIN has been sorted.
IF you were running a stock trans like I am, I would gladly share my tune with you, but I really don’t know what they have to do with shift times and pressures for aftermarket clutches and valve body upgrades, etc.

 

Thanks for the information. At no point were there any DTC's thrown. The A6 is a fully built version by Mike Kurtz at Century Automotive in TX. I am hoping that Mike can collaborate with my local tuner Geoff Skorupa at Next Level Performance in Longwood, FL. to diagnose and fix the issue without having to pull the trans and ship it back to Century. From what you wrote this seems like a possibility. Perhaps Geoff could pull the TCM and send it to Mike. Mike could do the magic to move the tune from the current TCM to a new TCM and send it back to Geoff to reinstall.

BIGMAC

 

I've experienced shift hesitation issues before, as well as having it feel like it has a trans brake but never at the same time.

When I had shift issues I just figured it was tired and time for a rebuild. When that didn't help I started tweaking my tune but no matter what I did it wouldn't shift properly at WOT. What ultimately ended up fixing it was replacing both the TCM and valve body. I can't say definitively that it'd fix your problem but if nothing else you'd know for sure what it wasn't and you'd also be at a known good starting point.

It was somebody else who had the trans brake issue and from what I remember it required a full rebuild in that situation.

What I would do if I were you is start by swapping the TCM and valve body to see if that ultimately fixes it. You would need somebody with a Tech 2 to program your VIN into the TCM and then somebody with HP Tuners to reload your transmission tune.

If that doesn't fix it then I think you'll need to bite the bullet and send the trans out to have it gone thru again.

 

Did you switch to MAF only or Speed Density only tune? When I was tuning my 07 the Trans did weird things when in either of those modes to data log. There is a switch in the the software that help this I believe.

 

I had something like this happen to my A6 this weekend. The car would not move fwd or back in any position like it was in fwd/rev at the same time. I rowed back through the shifter positions and finally got it to move, however, it moved in reverse in the Sport Mode position. I shut the car off and turned it back on, but now it kicked out a P0777. It would now not move again at all. I put in drive but it would just rev up. I finally revved it to around 4k and it popped into a fwd gear(hard). These transmissions are a PIA. Good luck with your troubles!

Century will be seeing mine soon.

 

My opinion ? the A6 is the worst trans GM ever made--Even worse than the 700R4
GM shorts shifts the trans into 6th gear way way too early like at 40-45 MPH at light throttle
The line pressure is so low that they will all eventually fail slipping badly
ALSO GM Locks the TQ converter on most all their vehicles from 1st or 2nd gear on up-Some 6 speeds will wait until 3rd gear---That is probably the hesitation you are feeling the converter locking up
At WOT the converter is mostly Unlocked ---however it still can be locked as it is MPH based on what speed and what gear you are in
This is very controversial among tuners how to tune a 6 speed auto
Some tuners will leave the converter UNLOCKED at P/T until 4th gear
Also some tuners will make the converter stay UNLOCKED all the time at WOT with simple tuning ----No one knows for sure what is the best choice--I work with many tranny shops and they are often stumped on what to do to make these trannys live
I see many silverados break after 60K miles with stock tuning--Some 6 speeds like the changes some don't It is crap shoot !!

 

Sorry you feel that way and can't find or don't have access to a good tuner.

My 100% bone stock 6L80 has seen a ton of passes & +800rwhp and still living doing just fine. Key is finding a GOOD tuner and keeping temps down. A stock 4L60 or even built wouldn't have held up to what mine has been through the past 5 years, FACT.

 

Looking for input, I have a stock 08 with 72K on it, this is my first and only A6. This thing is so mushy shifting and it feels like it almost kicks out of gear when you slow down to make a turn, is this a normal situation and if it is there a way to make it more crisp? TIA

 

Tuning has nothing to do with the 6L80E failures ---Some are good-most are bad--I have tuned over 1000 of these 6 speeds-- Visiting our local best trans shop the owner showed me 6 6L80E trannys he had received in his shop in ONE week ALL blown up !!!--He says the issues are all as I described --
Short shifting
Shifting into 5 and 6th gear at too low of a speed with very little line pressure
Weak TQ converters
Yes if you race or run your car at WOT most of the time it is actually better and will last longer than driving around town at slow speeds

 

Isn't shifting into 5th and 6th at too low of a speed a tuning thing? Or is that just RPM related? I also think heat has a major role in destruction.

 

What do you see as the most common failure parts wise?

 

Yes they also run way too hot Not uncommon for the fluid to reach 230-240* after only 30 minutes of city driving even with the factory synthetic fluid
These 6 speeds do not like to be messed with much --About the only thing we do as taught at EFILIVE training was to YES RAISE the shift points Normal city driving they will short shift before 2000 RPM's-----We raise the P/T shift points to make them shift in the "sweet spot" between 2000 and 3000 RPM's and not into 6th gear until on the freeway about 65 MPH
We never mess with the TQ converter settings
There are no "force motor current " settings as on the 6L80's that make the solenoids snap quicker creating crisp shifts and no
" pulse width modulation " settings as on the 4L60's to make the converter lock firmer
We only adjust the "shift times" very little like a minus 3-4%
You can drive a 6 or 8 speed around town with stock tuning for 30 minutes and it will up/downshift 50 times !!!!

 

Tuning has everything to do with the longevity of the 6l80 . First time I've ever heard anyone say that.... Heat is the major enemy to these trannys . Hand someone a laptop with HP tuners and let them tune on your car and see how long they last. The life of these transmissions are line pressures and shift points all controlled by the tune.

 

With HPTuners, you can make the 6L80 shift at a higher or lower MPH/RPM, Cut the shift time, and add transmission line pressure. And that's were I see shops make their mistakes. Adding to much line pressure the car then always shifts hard in stop and go traffic and a shop that dont know how to correct it, tells you, "that's our transmission tune"

I personally use the Torque Management tables to make a firmer shift not line pressure. This method is more taylorable for the owner and better when making the D mode for cruising, and M/S mode for racing. When using the Torque Management tables, the more throttle you apply, the firmer the shift will be.

 

Gents, the next personal attacks on this thread will receive sanctions. Attack the message, not the messenger.

 

These 6 and 8 speed auto transmissions have a thermostat that does NOT allow the trans fluid to circulate thru the radiator until the fluid reaches approx 220* Way too late--Does not matter if it is in a Corvette or Camaro or Silverado---Most transmission shops do a "thermostat delete" on these transmissions that allows the fluid to cool immediately without the thermostat thru the radiator --- This will cool the trans temps about 20-25* !!! It is a simple mod----Look it up online
"6L80 transmission fluid thermostat delete " and it will walk you thru the simple mod that will make these transmission live !!! by lowering the fluid temps

 

C6 corvettes DO NOT have a transmission fluid thermostat. Nor do they have 8 speed transmissions.

Please stop sharing information that is not true.

Everyone please disregard tblu.

 

I was speaking generically about most all GM 6L80's--Not specifically yours-- Of course C6 's do not have 8 speeds Quit nit picking my comments Or I will start nit picking yours
If you can say it so will I
PLEASE DIS REGARD ALL COMMENNTS AND INFORMATION FROM schpenxel;
He uses inferior tuning software and does not have the experience nor the knowledge that I have----after 16 years of tuning and over 3000 + tunes
But chooses to act like a child when someone dis agrees with him by making personal attacks
I am on this forum strictly to help people get information and sort thru tuning issues--That's it !! I have received countless texts and messages from forum members that I have helped in the past-- But there is always some wanna be that has to pick fights and nit pick every word I say I am flattered that he gives me so much attention

 

Taking the 8spd issue out of the conversation, you were very specific in inferring that all 6L80E transmissions had a fluid thermostat which could be subsequently deleted to improve the cooling.

Your words, nobody else's:

Now I'm bending over backwards here to be nice and not get in trouble with the moderator, but how could pointing out your incorrect information be considered nitpicking?

Also, even if you were given the benefit of the doubt and were truly talking about the 6L80E in general, how is it even remotely helpful to be suggesting something that doesn't apply to Corvettes, which is what the OP is seeking assistance with?