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6T70 Transmission Issues: And POSSIBLE FIX

So, I have a 2014 LT 3.6 with the 6T70 6-speed auto. I have read MANY discussions of troubles with this transmission. My Dealer (Deien Chevy in Trenton, IL) went to bat for me TWICE with GM after I had some symptoms, see below.

I purchased the car used in Jun2019 with 17K miles and some remaining warranty. Shortly thereafter I noticed an occasional very HARD upshift after passing at highways speeds. From say 50 mph, I would accelerate to 70 or 80 or whatever to pass. The car downshifted to pass, from 6th to either 5th or 4thgear. When I let off the gas to finish a passing maneuver, the upshift back to 6th gear was a VERY HARD THUMP. OH CRAP kind of hard. Alarmingly hard. It seemed to happen a bit more if the car was warmed up to full operating temps. For my car, that’s about 185 degrees. So, I took it in to the dealer and they were able to duplicate the problem.

So, my Dealer called GM to investigate. They wound up replacing the “TCM and valve body” under full warranty. I don’t have details on this repair, but it did not solve the problem. So, a few weeks later, I called the Dealer again and they tried again with GM.
This time the problem HAS BEEN ELIMINATED. This is the first time I can read where a 6T70 problem was stopped without an aftermarket tune, so I thought I should share. Below is the dealer writeup of the repairs. I asked them for as much detail as they could manage. I share this now in the hope that this is useful for some of you.
CHECK FOR HARD SHIFT AFTER PASSING ON THE INTERSTATE. ROAD TEST WITH CUSTOMER & THE BUMP SHIFT WAS HARSH ONCE THE ACCELERATOR WAS RELEASED. REMOVED THE TRANSMISSION AND DISASSEMBLE FOR INSPECTION. SEVERAL SEALS DAMAGED & AND THE 4 5 6 CLUTCH HOUSING GOUGED BY DEBRIS THROUGHOUT THE TRANSMISSION. THE SUN REACTION GEAR WAS COMING APART & THE DEBRIS WAS CAUSING THE DAMAGE. CLEANED CASE & INSPECT FOR DAMAGE, WAS OK. OVERHAUL THE INPUT REACTION OUTPUT CARRIER. REPLACING THE 1,3,5,R,4,5,6 (sic) SEALS AND 2 PISTONS. THE CLUTCH HUB HOUSING. THE 2-6 REACTION SUN GEAR, 1,2,3,4 CLUTCH SPRING RETAINERS AND PISTON. AS WELL AS THE GASKET FOR REAR PLATE AND SEALS. CHECKED THE TORQUE CONVERTER, WAS OK. REASSEMBLED THE TRANSMISSION WITH ALL NECESSARY SEALS AND GASKETS. INSTALLED THE TRANSMISSION. RESET TRANSMISSION ADAPTIVE SHIFT. FILL WITH FLUID AND ROAD TEST TO GET THE TRANSMISSION UP TO OPERATING TEMPERATURE, AS OK.
 

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Thanks, this is the first really substantial solution I have seen to the various random issues I have been seeing (hard shift after letting up on gas for a sec and then re-engaging gas, for me it happened in lower gears more). I will keep this in mind as I try to get my car worked on before my certified drivetrain warranty gets closer to expiring in two years.
 
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I am planning on taking the car in to the dealer once the COVID-19 money comes in. Yes, it is under drivetrain certified warranty for two more years, but that doesn't cover investigative work if they say they do not find a problem does it? The one time I called the dealer they said if no engine light comes on then there is no problem. That sounds like lazy bull$&!( to me. Are they basically saying my trans has to totally fail before they bother? SHould I consider biting the bullet and paying an independent shop to at least do the investigative work for the dealer?
 

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I am planning on taking the car in to the dealer once the COVID-19 money comes in. Yes, it is under drivetrain certified warranty for two more years, but that doesn't cover investigative work if they say they do not find a problem does it? The one time I called the dealer they said if no engine light comes on then there is no problem. That sounds like lazy bull$&!( to me. Are they basically saying my trans has to totally fail before they bother? SHould I consider biting the bullet and paying an independent shop to at least do the investigative work for the dealer?
That does sound like some BS. Especially cause transmission codes don't typically trigger the CEL. I noticed my 6T70 starting to develop weird issues (longer time to change from park to drive, ugly shifts, etc), and had no check engine lights. I plugged in my special scanner and it had 2 transmission codes. I had driven that way for a couple months and it never set a CEL. Mine ended up being blown pressure switch disks. I would try to get your hands on a scanner that does transmission codes to see if any are present. I would think the dealer won't accept a diagnosis from a different shop, so there is no point in getting it done elsewhere unless you are going to have the independent shop do the repair.
 

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That does sound like some BS. Especially cause transmission codes don't typically trigger the CEL. I noticed my 6T70 starting to develop weird issues (longer time to change from park to drive, ugly shifts, etc), and had no check engine lights. I plugged in my special scanner and it had 2 transmission codes. I had driven that way for a couple months and it never set a CEL. Mine ended up being blown pressure switch disks. I would try to get your hands on a scanner that does transmission codes to see if any are present. I would think the dealer won't accept a diagnosis from a different shop, so there is no point in getting it done elsewhere unless you are going to have the independent shop do the repair.
I have a cheap code reader and have never seen any consistent trans code thrown. Does the more expensive GM specific code reader report specific codes that the cheap OBD readers won't see? I have had an intermittent 0700 code, but it always goes away and the dealer says that code is pretty generic and a code has to consistently be thrown for them to do any analysis of a potential problem.
 

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I have a cheap code reader and have never seen any consistent trans code thrown. Does the more expensive GM specific code reader report specific codes that the cheap OBD readers won't see? I have had an intermittent 0700 code, but it always goes away and the dealer says that code is pretty generic and a code has to consistently be thrown for them to do any analysis of a potential problem.
I believe you need a code reader that can read from the TCM (although it seems some transmission codes may show up). My basic code reader could only read engine codes, and never showed my transmission codes. Not sure if that's maybe cause they were just pending? Could be. I have a bi-directional code reader now, so I can access each computer system individually and read the codes in them. Was kinda pricey at $700, but has more than payed for itself in saved dealer fees. Either way, I'd try to scan it with a more advanced code reader to see if there is anything pending or in the history.
 

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They charge for diagnostic if no problem is found. I got a check engine light and shortly after the tranny felt funny .i made a appointment and within 500 miles it was undriveable. turned out to be the torque convertor and they replaced under warranty. 2015 10th gen with 71K
 

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My 2011 Equinox 3.0L LT has the 6T70/75 transmission and so far, so good ... at 143,000+. But in recent months I’ve sensed some “flaring” where it seems like it’s “slipping”, but it’s never shifted harshly. I would describe it as “soft”, “wishy-washy”, or “imprecise”. Not sure if it’s always done this or not. I’ve changed the transmission fluid at least twice since buying it new, just draining and refilling what came out (typically 4.5 quarts).
 

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does anyone have info on replacing a trans from LKQ parts....would i need to get anything reprogrammed,or would it be a simple R&R.....i have a 2014 3.6 w/ 6 speed trans...
 

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does anyone have info on replacing a trans from LKQ parts....would i need to get anything reprogrammed,or would it be a simple R&R.....i have a 2014 3.6 w/ 6 speed trans...
Never done it, but I would think it's a simple Remove and Replace ... as long as you can transfer over your Transmission Computer (TEHCM)
 

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I think the local Chevy dealer has started to do service work beyond urgent stuff again now that states are starting to open back up again. So will be trying to get mine in for a look at the weird trans shifting (especially lower gears) and now also a very slight ticking noise under the hood that may have always been there???, I am not sure. If push comes to shove, maybe I will break out the original post on this thread and show them.
 

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Never done it, but I would think it's a simple Remove and Replace ... as long as you can transfer over your Transmission Computer (TEHCM)
The chevy dealer want's to charge $5400 to replace,comes with a 3 year unlimited miles warranty...so you think i need to take the tcm off the old trans and put it on the used trans ?
 

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The chevy dealer want's to charge $5400 to replace,comes with a 3 year unlimited miles warranty...so you think i need to take the tcm off the old trans and put it on the used trans ?
I would think so ... otherwise you'll probably end up at the dealer getting it re-programmed.

Here's an interesting thread on the Acadia Forum about replacing the TEHCM:

 
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