TSB Seems To Fix 8-Speed Automatic GM Transmission Problems
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We’ve covered the problems of the eight-speed GM transmission on numerous occasions. In fact, we cover a class action lawsuit brought against GM back in April, complaints from owners, and even a recommendation that GM replace the eight-speed altogether with a new unit as quickly as possible. Now, GM Authority has learned that there’s a new fix that seems to be alleviating the eight-speed’s shifting woes outright.
As of July 8th, 2019, GM began using a new type of Mobil 1 automatic transmission fluid for the troublesome transmissions. Customers that complain of shuddering and harsh shifting characteristics in the 8-speed GM transmissions are recommended for a trans fluid flush. As of August 7th, GM dealers should also be flushing all potentially affected new vehicles on the lot.
The GM 8L45 eight-speed automatic transmission
According to TSB (Technical Service Bulletin) 18-NA-355, the latest update addresses “torque converter clutch (TCC) shudder conditions on 8L45 and 8L90” eight-speed automatic transmissions, RPO codes M5N, M5T, M5U, and M5X. Affected vehicles include Chevrolet, GMC and Cadillac vehicles, as follows.
Chevrolet
- 2015 – 2018 Chevrolet Silverado 1500
- 2015 – 2019 Chevrolet Corvette
- 2016 – 2019 Chevrolet Camaro
- 2017 – 2019 Chevrolet Colorado
GMC
- 2015 – 2017 GMC Yukon
- 2015 – 2018 GMC Sierra 1500
- 2017 – 2019 GMC Canyon
Cadillac
- 2015 – 2017 Cadillac Escalade
- 2016 – 2018 Cadillac CT6
- 2016 – 2019 Cadillac ATS
- 2016 – 2019 Cadillac ATS-V
- 2016 – 2019 Cadillac CTS (excluding V-Sport models)
- 2016-2019 Cadillac CTS-V
The issues with the 8-speed GM transmission are two-fold. First, some customers report the transmission shuddering frequently. Secondly, the shifts are very harsh between first to second, and then second down to first, especially when accelerating and the transmission is upshifting or decelerating and the transmission is downshifting. These conditions are most commonly observed under light and medium throttle applications, and as often during full throttle applications.
However, a new fluid flush appears to fix the issues, with some customers beginning to report a dramatic change in shift quality after swapping out the old juice. If the flush doesn’t fix the issue, the next step may be to replace the torque converter, which could be glazed.
2016 GMC Yukon
The issue seems to stem from “moisture content in the transmission fluid.” As such, the old GM transmission liquid is swapped for new Mobil 1 Synthetic LV ATF HP fluid. Driving the vehicle for about a week or so improves shift quality even further as the new fluid cleans things up inside the transmission and the adaptive shift algorithms relearn various parameters.
This is obviously a big deal for owners struggling with their vehicle’s eight-speed. Hopefully the new fluid swap will provide a lasting fix.
Have you experienced shuddering and harsh shifts with your eight-speed GM transmission? Have you gone in for a fluid-swap fix? Let us know your experiences by posting in the comments section, and don’t forget to subscribe to GM Authority for 24/7 GM news coverage.
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Has anyone tried the Trifecta tune? Curious to see anyone’s thoughts if it made transmission better. Just ordered tune waiting for cable
Has anyone tried Trifecta tune? Curious to see if it made a difference. Just ordered tune waiting for cable
I’ve read where a few people say they got a Trifecta tune and it made a world of difference. If it were that easy wouldn’t you think that GM could do the same? Go figure.
I don’t believe GM can legally deactivate AFM. It would change the CAFE mpg. This may also change/cancel the warranty.
There probably is some kind of regulation for it. I have heard that tuning it out doesn’t change it, and that some owners even report slight gains. I mean the gains aren’t anything significant, like maybe 1 or 2 MPG, maybe more for some people, but it’s small. I think they’re probably on a similar boat with the transmission. Everyone is asking why GM can’t develop a tune like trifecta, and it’s probably the same thing. I’ve seen on here that they’re working on new software. If the regulation part is true, then it could definitely take a little time to develop that new tune, especially to adjust the variables to satisfy regulations, and now customer satisfaction. I’m not sure they’re doing software or not though, because someone said they heard they’re redesigning the valve body or valve body cover. Why did it take 5 years? Well, there’s multiple aspects of the transmission that can cause the symptoms everyone complains about. The engineers probably tested it, and let’s say they changed the fluid on one, and road tested it, they probably drove it for x amount of miles, and released the information to dealers, because they want to get a remedy out there. The problem is, it’s coming back time and time again. Plus you have numbers of vehicles that do not have an issue reported, or you have ones that were remedied by one of the bulletins from engineering, then apparently you have the ones that are still problematic Everything they’ve done sounds good. Everything I’m seeing here with the software or the valve body/ cover sounds good. There’s something going on for sure, but the cause will be known soon. How soon? Who knows? Everyone says the transmission is bad, and wants a new one, or redesigned one. Ok, however there’s something wrong with a component of that transmission whether it’s mechanical, software, fluid, etc. If transmissions are completely junked, why can you get a transmission rebuild, or even buy remanufactured transmissions?
Iam the one who reported the valve body defect.It was relayed to me by the Service Writer of the Dealership(Bradley Chevy/Lake Havasu,AZ.)where my 2020 Chevy 1500 6.2l 10 speed has sat for 5 weeks now(as long as i had it on the road).I have a feeling there are multiple mechanical/software issues contributing to the catastrophic tranny fiasco that is GM.I feel that it is a start,but not a final solution.My prior 2 chevys (5.3l 8speeds) were made in Ohio and had not ONE issue.This one was made in Mexico and well you know the rest…
It’s my understanding that the 10 speed transmission was the result of a joint venture between GM and Ford started in 2013. I wonder if Ford is sorry about that. It would appear to me that teaming up with GM to develop a transmission would be the kiss of death at this point.
I just heard recently Ford dropped the 10 speed after that collab.As well as the 9 that never materialized.Guess they knew more than we did.
Trifecta completely fixed my shifting issues!! You have to pay $710 for engine and trans recalibration. You have to have AFM removed completely. I had a Borla xs-pro muffler installed cause I’m so happy with the shifting now, I wanted to hear it shift and enjoy it. GM should hire trifecta tuner to fix their entire fleet of 8 speeds!!! Makes no sense. I’m telling you guys it’s so worth it! You’ll love your vehicle again. You also have to do the triple flush of trans fluid when your vehicle starts to shudder. Trifecta will take care of every single other issue with trans, even the ones you didn’t know were the problem until you install the tune. Super easy. Just plug it in and click a couple buttons, it’s obvious and self explanatory. Good luck waiting around for gm to fix you vehicle, you have to do it yourself before the stock software ruins your trans.
Great to hear i only paid $669 for tune and thats Canadian. I thnk and hope it’s both engine and transmission calibration. Ordered it through Trifecta Ottawa
That sounds about right, engine $4ish and trans was $3ish. When you get the cord they’ll ask for additional info, have them remove AFM in sport and eco mode. I left AFM on in eco but still had a surge when going up hill with it being bad enough to downshift, thought it was trans related but had AFM turned off in eco a couple weeks later after talking to trifecta BAM haven’t had a single issue about anything again. I turn sport mode on in traffic but usually leave in eco mode. I live in the country so no need to fly. But I can if want with little effort. Your gonna love it I promise!
I had them completely turn off AFM have been using Range device since a year and like the way it works. MPG didn’t change worth talking about. Excited to see what tune will do.
Did it get rid of the lurching/ clunking at low speed 1st to second shifting?
Definitely, why GM is sitting on the fence all these years makes me wonder why?
The timing on the trannys is garbage as a whole.My loaner vehicle(Blazer) always feels a gear off,especially downshifting.It should not feel as if youre engine braking on a substantial decline when you are doing 20 on a flat surface and let off the gas.The AFM,auto kill all that is pointless and i have a feeling that contributes to alot of these issues as well.
Sorry for this being so long!! I drive a 2017 Chevy Silverado 1500 (midnight edition) with the 8-speed transmission, with approximately 80500 miles on it as of now (I bought it new). Sometime year before last (around 60000 miles in 2018) I started experiencing horrible shift from 1st-2nd, very aggressive jerks after taking it out of park and putting it in drive, and constant steering wheel shakes in and out of cruise control at any speed. When I would take it in to a dealership for warranty maintenance (oil change tire rotation etc), never once did they suggest doing a transmission flush or anything of that nature. Was told “it’s just something Chevy’s do”. So after doing some research I found myself here reading all of your comments and suggestions and after doing more research I found out transmission flushes can cost between 200-600 bucks (Texas) and doing that twice and the though of being out of a vehicle for a day or so I didn’t want to pay more then I had to.
So I did it myself, I bought a evac system from amazon ($150) the transmission fluid suggested by Chevy ($120 16qts) a transmission fluid filter($20-30) and a jack set, at this point I had 76000miles on the truck. So once I hooked the hose up to the transmission cooler I noticed the fluid was very thick and dark almost like mud with to much water (Quick shout out to GMC for designing the exhaust pipe to go over the transmission fluid pan (STUPID). Now moving to the pan, after taking out the plug on the side of the transmission and pumping out the transmission fluid, it was the same constancy. Then I had to drop the pan (its gonna take some time!) The pan looked like a kid baked a bad batch of brownies and tried to wash it. So after cleaning the pan and magnets I found two pieces of metal the size of eraser shaving and very fine metal stuck to the magnet. After cleaning all that up and putting it back, I pumped in 7 qts of the new fluid. So now at 80500 miles I no longer have stutters. hard shifts, truck runs like new, there hardly any hesitation when I floor it getting up to speed without the stuttering makes me feel like I’m not losing even though i still owe 20k+ on this truck.
But here is the negative side to changing to the suggested fluid. Expect to see a significant drop in mpg, I remember getting almost 26-30 to the gallon, now its almost the high end of 19. The 4 speed icon rarely comes on and if it does it’s because I’m going downhill, idk if that’s a negative for you but I miss the high mpgs. One thing if you do want to go and just get the flush, they don’t drop the pan to actually clean it out or the magnets they just hook up the hoses and run the system until your fluid comes back clear, nor do they change the filter. I think this is why so many people keep having to go back to get the flush, it’s like installing a dirty filter in your ac at home like damn this air smells stale. Now once again I’ve only done this one flush and it’s been 4500 miles still have 0 problems, no check engine light no weird sound no leaks nothing. It took about 2.5hrs to do because it was my first time. But with all this I will not be buying another GMC product especially after making a statements like “it worked before you drove it off the lot” and “oh well it was someone else’s design” makes me feel like i got hustled.
Sorry if I missed it, but you say you bought 12 quarts of Dexron-VI trans fluid. I only saw that you put in 7 quarts. That would be like a pan drop and filter change and leave almost half the old fluid in the trans. Did I miss something?
I bought 16 so that I could do the flush twice but after pumping out the fluid there was only 6.9 quarts in the container so I put in 7.
I have a 2017 Yukon XL. I have had this problem for a couple years now. First time I took it to the dealer, they said it was fine, nothing wrong. Second time, they said it needed trans flush. Did that. Third time they said it was Fuel Injector #4. I asked them to guarantee their work, that this would resolve the issue. I told them that it did not make ANY sense that a fuel injector malfunction would cause hard shifting. They assured me that their lead mechanic researched the issue and this was the proper fix. Problem persisted…they said it’s now another injector…I gave up. I drive a $60,000 piece of sht. Hoping for class action resolution, retained attorney in the meantime, will be filing suit sooner than later.
It looks like General Motors is going to have the class-action dismissed. Your best bet is to Lemon Law vehicle which is really hard to do or go to a third party Tune which I think is called trifecta. It’s pretty much disables a lot of that garbage software ithat supposedly helps the mileage but more or less gimps the transmission. I would not wait for GM to fix this as they’ve been working on it for over 5 years. I’m not sure GM can disable those features legally you have to take things into your own hands as for the shutter that’s probably fixed with the fluid change but the hard shifting seems like a software issue.
I ordered the Trifecta tune still waiting for cable to arrive. You are correct i wouldn’t hold my breath waiting for GM to fix this 5 years come on. That’s why i ordered tune had enough of all these attempts at a fix.
Just remember once you receive your cable and they ask additional info, have AFM removed in eco and sport mode. Hopefully you purchased the $710 tune for both motor and trans. Your going to love your vehicle. It’ll run and shift as smooth as a import car! Not to mention the extra HP! My truck will cruise all the way up to 80 barley touching the pedal and shifts exactly where it needs to! Please let us know how much you like it! Good luck man!
Ryan i purchased both for $669 Canadian from a dealer in Ottawa. I had them turn off AFM completely because its garbage and for the little MPG gain not worth it plus the damage it can do if it drops a lifter. Looking forward to see how it will performs. If it does what it says ill advertise it here .Will let you know definitely. Thanks
Who sells these tunes?
Trifecta
Why is the Class Action being dropped? It is obviously a flaw.
GM attorneys are fighting the class action to the end according to stuff I’ve read….not holding my breath of getting any resolution out of this….this can drag on for years!
Anthony please report back once you have installed it.
I am interested in the trifecta only if it gets rid of the delay on the 1st to 2nd gear delay that happens on cold start first one of the day that GM says is normal .
Yes i will if i can find you among all the comments Scott hahaha
Anyone who had the flush recently, did it fix the issue? They’re currently wanting to flush mine now and saying they have a new fluid based on March 2020 but the TSB he gave me is still the August 2019 TSB…trying to figure out if I’m putting good money after bad. Has anyone had any luck with getting GM to offer Cost Assistance when out of Warranty?
I just had my fluid flushed at beginning of July along with temp sensor replaced and two new harness. After 800 miles of driving I am currently OMW to dealership again to get them to look at it for shudder at highway speeds still. The hard first to second has been fixed but now there is a hard second to first downshift that makes it feel like I just got rear ended or the rear end is loose.
I had the flush performed on my Corvette about 6 weeks ago. So far it has helped. I had the flush performed maybe 6+ months ago on my Cadillac and it didn’t help at all. I really want the Corvette flush to fix it forever but the Cadillac is headed out the door as soon as I can find a reasonable “Non-GM” replacement. The Silverado got traded on a Ram in April. The Corvette is GM’s last chance to keep me as a customer. The GM transmission problems have cost me $thousands$.
I had another flush done 3 weeks ago, per that bulletin. The flush did not resolve the issue. Problem returned the next day in route to work (33 miles one way). Truck went back in the shop for a torque converter. An entire week then went by, and the converter was not installed. I was told GM is waiting on another solution. That was it for me after 1 year and 7 months (new 2019 Canyon). I drive an F-150 now. I just hang around here to see if a concrete ever presents itself.
Had mine done in recently 17 GMC Sierra…..worked fine for 1 day….waste of money
I am on my second flush as well. The tech said the truck was not even driveable, but GMC will likely do nothing about it. He seemed very genuine and knew how GM operates
(Black label) Mobil 1 Synthetic LV ATF HP transmission fluid Is the new trans fluid that GM dose the triple flush to take care of the shudder, hopefully before you cook the torque converter. The old fluid (Blue label) mobile 1, it would build moisture In it, that’s what causes the shudder. Dealer did mine for free. I’ve seen it cost $500 For the triple flush. O’Reillys has “lube guard platinum” that actually says “shudder fix” on the bottle. my Colorado takes 2 little bottles of it. I bought a gear oil pump to removed a sprite 20oz bottle worth of trans fluid before I added the 2 bottles of lube guard, it says on the bottle it can be added to a full trans and won’t hurt anything but I removed some before I added to be safe. You might be able to add it to the old fluid to save money. I didn’t have that problem anymore after doing both.
7.31.20 2018 Sierra 8 Speed transmission shudder: I have had the same issues with my truck. Currently have 20K miles. The fluid was changed today at the dealer. They used the Mobile fluid and it has corrected the issue. I will post another update if the shudder reappears.
My question is whether one fluid flush is enough or should it require two? The transmission guy drove my truck. He told about the issue and stated that it will need two flushes to fix the issue. However, the service guy today stated that it is all good to go and that one flush addresses the issue. Hmm..
Most posts are 2017 2018 8 speed trans. I have a 2019 silverado built 2/2019 with all the same shuddering, hard downshift 1-2. Delay 1 st startup from rev to drive. now at 18k it is lurching significantly 1-2 in slow moving traffic. Do alot of 2019s have the same issues or did I just get lucky/s
Ryan,
When I get a chance I am going to try to dig through the older versions of the TSB. My memory may be flawed on this, but I thought the old verison of fluid that absorbed water was the black label and that the new “does not absorb water” fluid was blue label. Part numbers would be very helpful. The blue label Mobil synthetic specified in the 8/2019 version of the TSB 18-NA-355 (is there a newer verison? ) has a part number of 19417577.
Also, a version of the TSB prior to the 8/2019 version specified changing the fluid 3x. The 8/2019 version calls for a single fluid exchange.
So, unless there is a new version of TSB 18-NA-355, then it may be possible that your dealership has confused an old version of the TSB with the current one. On the other hand, I suppose that it is possible that GM has yet another new fix that has not gone out to everyone in the form of a revision to the TSB, and your dealer has been given that info ahead of time by a regional manager or something. I would love to know for sure.
I’m pretty sure I switched the blue and black labels. I forgot to add vise versa.. sorry about that!
My 2nd flush in Nov 2019 was done under TSB 18-NA-355 using part # 19417577 which is the new blue label.
My 1st flush in Sept 2017 was done under TSB 16-NA-175 using part # 19353429 which is the older black label.
I have a 2017 Sierra with 25k miles.
Has been in the dealer 3 times for same issues.
1st: Software Upgrade – no fix
2nd: Tranny flush – no fix
3rd: Software reset for adaptive shift learning
(Better but not fixed)
Currently when in manual shifting and in 3rd gear and shifting to 2nd it jerks and I hear a loud clunk. I contacted GM and they are aware of the issue and are handling my case. (I hope they do something) not holding my breath though.
But I’m persistent, I hope I can get this resolved, I love my truck just can’t stand the shifting issues.
I have a 17 GMC Sierra Denali…65000 miles..been to dealer several times..still clunking when shifting…tired of trips to dealer…I’m going to drive it like it is….its either going to last or take a dump…
Guys, have been tuning GM vehicles for quite sometime in the aftermarket world. I bought a sixth generation Camaro myself, and noticed the same shudder at low speeds in between 1000-2000 RPM. If you observe closely, the RPM’s jump fifty or so RPM up and down when it occurs. It is not the trans fluid, it is the TCC locking up the engine at the wrong time with the wrong gear. Fluid flushes and new converters will solve nothing as you can see by the amount of people stating the problem keeps coming back. You need your TCM tuned by the aftermarket because GM is clueless, as are their techs. Find someone local experienced with HP Tuners, and get it done. HTH…