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6T70 Transmission Issues: And POSSIBLE FIX

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6t70
47K views 27 replies 16 participants last post by  hatzie  
#1 ·
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.
 
#2 ·
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.
 
#26 ·
I have a 2014 impala with 64,500 miles on it. Haven't had any problems with transmission. Hopes it stays that way. Sorry to here you had a problem with yours. Of course changing trans fluid at recommended intervals. Filter is inside transmission. Extra cost to service it.
 
#5 ·
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?
 
#6 ·
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.
 
#9 ·
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
 
#10 ·
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).
 
#12 ·
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)
 
#13 ·
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.
 
#17 ·
This sounds like a whole transmission rebuild. My car does this HARD shift when I speed up to pass then let off the gas. It has also developed a "shudder" when I'm accelerating, especially going uphill. No check engine lights are on. I bought my 2014 Impala LT2 3.6 (new model) new in October 2014 and now it has 169K on it so I don't have a warranty on it. I know I won't pay for a new or rebuilt transmission, it has never worked out for me in the past on other cars. I have not done a transmission flush on it ever bc I've always heard so many bad things about them. Does anyone have similar issues with a trans shudder and if a flush will help?
 
#18 ·
Fwiw, my shift points seem much improved when the traction control nanny feature is turned off. Kristy, I'd recommend a tranny drain/refill, no flush. If your car is similar to a '16 Limited, there should be an 11mm drain plug just inside the lf tire on the tranny case bottom. Slide a 6qt.+ drain pan underneath the plug and remove. Refill with 5.5 qts. of Dexron 6 atf through the underhood dipstick/cable tube. Do this each 30k mi. No pan to drop or filter to change making it easier than an oil change. I personally don't even jack up the car for this. Do this on a cold engine.
 
#21 ·
My 2011 Impala with the 6T70 tranny all of a sudden today with no prior warnings (such as early gear slipping, difficult shifting, Check Engine Light(s), etc) lost all accelerating power in ALL GEARS. The Tranny shifts into Park no problem and it actually engages the car into park (preventing rolling), I can shift into R-N-D-3-2-1 but only my rpms move up as if in neutral. Not low on transmission fluid, and its not any different than a vehicle looking like a tranny fluid change may be due in the upcoming future, but no immediate issues apparent in the fluid.
I shut the vehicle off for a minute, BOOM power is restored in all gears...for about 30 seconds. I've repeated this a few times where I shut the vehicle off for some time, turn it on again, & there is my gears all engaging with regular power again...for however brief a period of time.
Only 182k on the odometer, like I said, no check engine lights are on, & upon turning off and on accelerating power is restored, albeit however brief a period of time.
I need to know what the possible cause of this is, and is it repairable by myself, or requires a rebuild, or replacing of the transmission. also i checked the 10a fuse which looks fine. am at a complete loss as to troubleshooting this issue. Anyone with experience in similar issues please lmk and respond. I'm about to lose my job and house if i cannot be mobile. HELP ANYONE
 
#22 ·
Just for future reference, you do not have a 6T70 transmission in your 2011 Impala (this transmission started in the 2012+ years impala). You would have the 4T65. Sounds like you aren't building line pressure for whatever reason. I would think that it likely needs a rebuild, but I am certainly not a transmission expert. Best bet is to bring it to a transmission shop to have it looked at. If you are handy, you could swap the transmission with a junkyard one, but I doubt you are going to have a simple fix, like switching a sensor or something. Either way I would start with getting it diagnosed by a reputable transmission repair shop in your area.
 
#24 ·
Does anyone know how much a guy can expect to pay to have the transmission filter replaced..currently driving a 2017 impala lt with just under 106000 miles..I usually get work done at my friends shop that is independently owned..thanks
 
#28 ·
You have to open the transmission to get to the strainer. It's a 150-200 micron or so. It's a pickup screen not really a filter.
If you really want a filter get a Magnefine inline filter, install it in the cooler return line, and change it every other oil change. The way I do things that's 10,000 miles or so.

The flush machines I remember from the 1990's and the first decade of this century that force the fluid back in under pressure tend to be bad mojo.
If it's an exchange machine that hooks inline with the cooler return line to swap 100% of the fluid using the transmission pump that's OK. BG makes one among other outfits. They're a sweet piece of kit but they're cost prohibitive for Joe Sixpack. I've seen them as low as $700 used but that's too expensive for the once a decade use I'd get out of one. I can go to a buddys' shop that owns one and let him do an initial fluid swap on my new jewel.

I'd just drain it and re-fill with Dexron VI, run 500 miles, drain it and refill again. If it's still a little dark go another 500 and change it again. Once it looks clean and bright red I'd change the fluid every 2-3 engine oil jobs after that.

It's easier than an engine oil change since you aren't messing around with a filter. Not that the spin on filter is that big a deal. Just drag the drain pan over under the transmission, pull the plug, drain, put the plug back in along with the oil pan plug, then go up top and fill engine with oil and the transmission with Dexron VI.