Post New Transmission: Infamous Clunks

on a side note, if you are stuck and want to flash the oem tranny tune yourself, you can do it for 150$ dongle, a newer computer with enough specs for the acdelco website and 40$ for their license fee.

I've done it, it wasn't bad besides gm website being glitches at times. way eaiser than any of the cracked China stuff. I think hptuners would be money better spent, even if it's more.

edit hptuners is easier to use and you could save the current tranny program you paid for so it's not lost, flash a stock one for a test. the gm site will overwrite whatever in there now and be lost. plus you could post off the file you pull from it and after others take a look to compare to what they run.

j91z28d1 said:

yeah, I was going to say, who ever tuned it can flash it back to stock as a test right? you don't have to have a dealer do it. it would also tell you if the tcm was replaced or not. as the new one would need to be re credited?

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Can only tune it back to its original IF they kept the original "read" file..
I've downloaded the "stock" tunes from the HP repository just to compare stuff and
it seems like it's a bit different at time too... So getting the original would be the best
and then do your mods from there.. Otherwise just mod what is there and would
need to buy 1 more credit for the TCM part...
But it sounds to me like it's not necessarily a tune issue at this point

NVM

j91z28d1 said:

I'm curious who tuned the tranmission?

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Misunderstood. The new transmission was programmed at a GMC dealer in Greenville, OH (Hittle GMC).

gbink53 said:

Well good luck. I’m getting real sour on GMC. My 2020 XL 50K miles, as I posted earlier had clunking sound, thought it was transmission but dealer says it’s torque converter. No OEM replacements in stock, back ordered for months with no ETA in foreseeable future. Now no loaners either but they sure want me to rent one at thousands/month. Awaiting attorney to call after they research issue. $70k immobile paperweight.

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I've heard these horror stories in West Michigan, too. It's a class action suit in the making for GMC.

Foggy said:

My guess is that the new trans is just the stock calibrations.. And that whomever tuned
the vehicle last year did some of the normal mods thru HPTuners that makes the
6L80E a "nice" transmission to have. (personally imo the factory settings suck!)

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This is exactly what happened.

Once it was deleted, they did a special tune for performance especially when towing. Assuming it was done in tow mode but not sure. The downshift happened a little before the transmission blew but now it's a ton worse. So whatever settings the GMC dealer did with the new transmission probably overwrite the customer TCM settings.

Trouble is, now I can't get in to the guy who did the custom tune and I have to tow my camper back from Ohio next weekend. I don't even want to try out of fear of blowing another transmission. I really am stuck right now, which sucks going into a holiday weekend.

I'm no transmission guy but I would think the gm dealer would only flash the newest oem settings for your truck. I believe it requires the vin to even download the software. are you thinking a brand new tranny would blow up towing with the oem tune? is this a really heavy trailer?

if you need a aftermarket tune quickly, it seems black bear is highly regarded here. would they possibly be able to load you a tune and ship the flash module to you in time?


this whole time I thought you had an aftermarket tune in you new tranny causing harsh down shifts and clunking. I was under the impression the stock gm tune gave up reliability for smoothness and mpg

I believe you can rent a Ford f250 from Hertz car rental if you need a heavy duty tow vehicle.

j91z28d1 said:

I'm no transmission guy but I would think the gm dealer would only flash the newest oem settings for your truck. I believe it requires the vin to even download the software. are you thinking a brand new tranny would blow up towing with the oem tune? is this a really heavy trailer?

if you need a aftermarket tune quickly, it seems black bear is highly regarded here. would they possibly be able to load you a tune and ship the flash module to you in time?


this whole time I thought you had an aftermarket tune in you new tranny causing harsh down shifts and clunking. I was under the impression the stock gm tune gave up reliability for smoothness and mpg

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Was able to get it back to Baker Engineering to put the tune back on. Seems to be better but still some minor clunking. Not sure where to go from here.

tkdgirl said:

Was able to get it back to Baker Engineering to put the tune back on. Seems to be better but still some minor clunking. Not sure where to go from here.

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Clunky shifts usually indicate weakness in the compensator feed and exhaust backfill hydraulic circuits inside the transmission. Those two circuits regulate shift timing, feel and prevent centrifugal apply of the front three clutch packs in the transmission.

If subsequent tuning doesnt resolve ( it likely wont) but it doesnt get any worse, just drive it. However if you start to notice the clunks get more frequent and/or harshness increases, next step would be a full diagnosis to include electrical, vacuum testing of the TEHCM and Valve body assemblies, respectively. Speed sensors would also be checked...