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GM 8-speed transmission

40K views 122 replies 42 participants last post by  Dougyfd  
#1 ·
From GM Authority:

[h=1]The GM 8-Speed Transmission Needs To Go Away ASAP: Opinion[/h]


It’s no secret that the GM 8-speed transmission is not great. Also known as the 8L90 and 8L45, the 8-speed pairs to rear-wheel-drive architectures in GM’s bread-and-butter products, including pickup trucks, SUVs, sports cars and luxury cars, and to say that it has a few issues would be a major understatement. Owners have complained far and wide about the 8-speed’s strange tendencies, such as waiting too long to upshift, downshifting at odd times and lurching when coasting or coming to a stop light. Long story short, GM needs to do away with the 8-speed and replace it with the much-improved 10-speed automatic… and quick.
In fact, GM was recently slapped with a class action lawsuit over the 8-speed gearbox. The plaintiffs assert the GM 8-speed transmission is defective, creating violent shakes, jerks, and a “hard shift” when selecting a gear. For its part, GM has filed 13 technical service bulletins concerning the unit, none of which remedied the issue. Following the lawsuit, more owners have spoken out over the issue, and we’ve even heard from our own readers about it on our forums.
The issue seems to be most common when accelerating or decelerating as the transmission tries to find another gear, with the problem believed to stem from the torque converter as well as the gearbox’s shifting logic.
Following a litany of complaints, GM tried to “improve” the 8-speed in the 2019 Silverado and 2019 Sierra. In a press release, the automaker said it made “enhancements designed to improve shift quality, while also adding a new centrifugal pendulum absorber torque converter” to improve smoothness. The new revised transmission was assigned RPO code MQE, replacing the M5U 8-speed unit on the half-ton Silverado and Sierra, but not (yet) on other GM products like full-size SUVs or mid-size pickups.
Taking all that into consideration, The General seems to have grossly mishandled the entire situation with the 8-speed transmission. What it should have done is replaced the GM 8-speed transmission outright with its new 10-speed automatic (jointly developed with Ford) in every vehicle application. Of course, that would have required some doing, as the GM product lines that would qualify for the change-over today include:

Previously, the GM 8-speed transmission was also used in sunset models like the Cadillac ATS, third-gen Cadillac CTS (except for the CTS V-Sport, which used an Aisin eight-speed), and the 2016-2018 Cadillac CT6 (the vehicle switched to the 10-speed transmission for the 2019 model year). In addition, the GM 8-speed transmission was also used in the 2016-2018 Camaro LT and SS, along with the now-discontinued C7 Corvette (apparently the 10-speed was too wide to fit into the C7).
[h=3]The GM Authority Take[/h]To play armchair quarterback for a quick minute, The General should have bitten the bullet and replaced the GM 8-speed automatic transmission in any applicable vehicles with the new 10-speed unit as soon as the new 10-speed was launched, no matter if the model was due for an update, refresh, or overhaul, or not. Instead, The General dug its heels in and continued to offer vehicles with the lackluster 8-speed, going so far as to launch all-new products – most notably the 2019 Silverado and 2019 Sierra – with the 8-speed that was “improved,” but that didn’t deliver any noticeable improvements.
Sure, switching to the 10-speed mid-stride would have created additional expenses and required additional engineering work. So yes, it would have cost GM money. But wouldn’t those funds have been well-spent when compared to the gobs of money GM will probably end up spending in legal fees to defend itself (and potentially pay out on the class action), while also causing reputation-based damage as a result of customer dissatisfaction in its bread-and-butter products, thereby potentially losing customers for life?
Why, yes it would have.



Read more: http://gmauthority.com/blog/2019/06...g/2019/06/the-gm-8-speed-transmission-just-needs-to-go-away-asap/#ixzz5rE2lWBYA
 
#2 ·
Terrible transmission! Harsh, finicky, and sluggish - adjectives you'd want to avoid when describing a transmission.

To date, the best automatic transmission I've owned was the 5-speed found in the 2006 Acura TSX. The transmission was quicker to shift and had excellent engine braking, excellent control.
 
#4 ·
I've had mine in twice for the herky-jerky. My dealer had never heard of the latest TSB. I had to tell them about it which is why I went back a second time.
 
#6 ·
#8 ·
Had my fluid flushed under warranty, a replaced torque converter under warranty and another recent flush on my dollar. This morning, had a violent bang shift, 1 to 2 gear, on a fully warmed up tranny. I'm afraid we are going to have to live with this problem to the very end. Shame....the tranny was brilliant at COTA!!
 
#11 ·
Had the flush done, appears to have sorted out the shudder, which was in it's beginning stages on my car. I wasn't getting the rumble strips effect, but rather a stuttering at low throttle in high gear when going uphill. I also had the coupling/uncoupling at highway cruise. Seems to all be gone now. As others have stated, the 1-2 is still sometimes harsh, but that is always after a first startup.. doesn't seem to matter whether the car is warm or cold. The "fix" for me has always been to start out in M1 when I am going through a parking lot, etc.

I'm eager to see if a recall will happen. I just think there will be lots of resistance to it from the bean counters at GM, because of the number of vehicles that have the 8L90. It will be a very expensive recall for them, even if they limit the work to a flush and valve body replacement. Replacing the TC on tens, maybe hundreds of thousands of vehicles will be very costly, and I could 110% see GM trying to weasel out of that.
 
#12 ·
Had the flush done, appears to have sorted out the shudder, which was in it's beginning stages on my car. I wasn't getting the rumble strips effect, but rather a stuttering at low throttle in high gear when going uphill. I also had the coupling/uncoupling at highway cruise. Seems to all be gone now. As others have stated, the 1-2 is still sometimes harsh, but that is always after a first startup.. doesn't seem to matter whether the car is warm or cold. The "fix" for me has always been to start out in M1 when I am going through a parking lot, etc.
So I just had mine done too, for the exact same issue. The shudder and coupling/uncoupling at highway cruise is gone. However, the issue persists where gears 2-3, 3-4, 5-6 are a bit harsh and sometimes it feels like the gear is slipping a little bit. Does your car exhibit those symptoms? I have the dreaded 1-2 when I first drive off in the morning but after that the 1-2 is fine.
 
#15 ·
I believe the latest shudder TSB has been posted her. Need to search for it. It is in 2 parts and many pages long as it covers all the cars using the A8.

I have two 8L90s. The one in my 16 Corvette Z06 is not terrible but definitely is not as good as the one in the 18 ATS-V. So they have made some improvements.
 
#19 ·
Fords always stunk. I thought GM were supposed to gone solid
So I just had mine done too, for the exact same issue. The shudder and coupling/uncoupling at highway cruise is gone. However, the issue persists where gears 2-3, 3-4, 5-6 are a bit harsh and sometimes it feels like the gear is slipping a little bit. Does your car exhibit those symptoms? I have the dreaded 1-2 when I first drive off in the morning but after that the 1-2 is fine.
mi e runs poorly when hot
 
#48 ·
Terrible transmission! Harsh, finicky, and sluggish - adjectives you'd want to avoid when describing a transmission.

To date, the best automatic transmission I've owned was the 5-speed found in the 2006 Acura TSX. The transmission was quicker to shift and had excellent engine braking, excellent control.
I have a late model year 2016-V automatic coup. I have been following all the threads about this transmission. The only behavior that I have experienced with this transmission is that cold start initial harsh 1-2 shift. And after the car is warmed up even that goes away. If a want and have time, I will sit and let the car come up to operating temperature, and then the harsh 1-2 shift does not even occur. There is no "shudder". and all other shifts are perfectly fine. I read the TSB about the transmission flush and re-fill with the new Mobil 1 transmission fluid. I was in the dealer yesterday for an oil change and we had a conversation about this topic. This is an individual with years of experience that I have been going to for years. I trust him. He remarked that people have been coming in and requesting, even demanding that this TSB be performed and after wards, the transmission winds up with problems that it never had before. He asked me if I wanted to "roll the dice"? I declined to do it. Those of you thinking about doing it, IMO, should think long and hard about this decision.
 
#25 ·
Ive had all of the above problems with mine jerky first gear, confused shifting, and converter highway surge.The tcm relearn wont do a thing and it will just come back.You need to have the TSB for the triple transmission fluid flush with the new fluid for this issue to be gone.I had it done on mine and it is honestly a different car to drive.I have driven cars with the new GM 10speed and it drove even more confused than the 8speed honestly
 
#32 ·
From what I've learned the problems are separate but indirectly connected. In otherward, you can have the shudder and have it remedied by the new fluid and flush TSB but if its been going on for a while the damage may have gotten to the point where the harsh shifting is still and issue. At that point they do the torque converter.

I noticed the harsh shit got noticeably better after the shudder TSB was performed but no after 10k miles the harsh shifting is returning. I may see the dealer again at some point.
 
#28 ·
Change dealers is the best you can do. My tech told me as we were on a test drive that the dealer must verify certain codes that are specific to your vehicle (and VIN) and they must have this code(s) in order to be reimbursed by GM.
 
#29 ·
I agree with tinman. You may have to change dealers. At my Cadillac dealer, I described the 1-2-1 hard shift. The service tech said they had a new TSB to address the problem. They flushed the tranny fluid and refilled it with Mobil synthetic fluid. They said give it about 400 - 500 miles to correct itself. After about 400 miles, the 1-2-1 hard shift is gone! Whew!
 
#30 ·
I have a 2016 that has no shutter and only an abrupt initial 1/2 shift in the morning and after that no issues whatsoever. By the way no blue smoke issue either. I have observed that if I let the car sit until the oil temp comes up until a little below normal operating temperature that there is no abrupt shift at all. Just the same, next time it is in for service I will ask that the transmission be flushed and refilled with the Mobil Synthetic as per the TSB,
 
#31 ·
I used to have the harsh 1-2 shift, and the shudder. I had the first TSB performed and it took care of the shudder for a while but it came back. But, after driving the car for a while, the shifting if pretty smooth, or at least acceptable. The 1-2 shift deal is totally gone. Now that it looks like they have a real solution for the shudder, I will have the dealer perform the fluid swap again at my next oil change.
 
#33 ·
I think the 8L90/8L45 is a pretty good design.

What was bad in it's first couple of years was GM's transmission fluid formulation. That was the cause of the shudder problem in the vast majority of transmissions which exhibited that characteristic.

GM went though at least three iterations of ATF for the 8Lxx transmissions. The last time I checked, GM had decided that Exxon-Mobil's "Mobil 1 LV ATF HP" (stands for low-viscosity, automatic transmission fluid, high-performance) is what should be used in those them. My belief is GM, also, replaced some torque converters and even whole transmissions because their clutches were degraded by the chatter/shudder caused by the ATF problems. I advise anyone who is not using that fluid to have the trans flushed with it immediately. Also, don't be tempted by some of the aftermarket Dexron 6 fluids. The HP additive package is far different that the Dex6 additive package and using Dex6 in an 8Lxx may damage the transmission. Right now there are few aftermarket ATF choices which meet the "Dexron HP" specification.

I have two 8L90s (one in an ATS-V and the other in a Corvette ZR1) and one 8L45 (in a Chevy Colorado ZR2). None of them have exhibited the shudder issue. The only negative is with the one in the ATS-V and I think that's more of a calibration problem rather than a transmission mechanical/hydrauic problem and that is: occasional hard or delayed upshifts in lower gears during very light throttle operation.

As for the 10L90, while the 10-speed auto might be a better transmission, some reasons it might not be used in place of the 8Lxx are:

1) Cost

2) No advantage over the 8spd. In some lighter, non-high-performance cars and light trucks, two more gears won't achieve much improvement in fuel economy.

3) Architecture. The 10L90 is a longer transmission and may not fit some platforms without costly redesigns.

Lastly, some folks may not know that the 10L90's core was developed by a partnership between Ford and GM.
 
#35 ·
The 18-NA-355 has been modified and in fact renumbered. No longer is the shudder verification via picoscope necessary. GM also has reduced the labor payment to the dealer accordingly. One flush with the new fluid per car under warranty. They must like the new fluid and say that it has "fixed" the shudder problem. Had the Z06 done 3 weeks ago. Only put 200 miles on it so far and they now say 300 miles to get full effect. The day after the work the 8L90 was very confused and exhibited all sorts of shifting issues but that was with only 8 miles on the new fluid. Now with 200 miles the car shifts as it did which was smooth with only the cold first 1-2 shift and I believe that is much less jerky than before. But that first 30-40 miles was pretty brutal so I saw how bad the shifts can get up and down. However as the fluid got itself distributed around the system it got smoother and now it is really pretty good. My shudder was intermittent so couldn't do the flush as I couldn't count on them diagnosing it. With the new TSB, that wasn't a problem. So far no problems with the 8L90 in the ATS-V but I only have 10,000 miles on it (2018). That A8 is perfect. No harsh shifts, no shudder so far, and much much better programming than the Corvette.