My own 8 speed problems & resolution

brendan4862 · March 1, 2016

Hello everyone!

Love these forums! Great site and everyone is super helpful.

I wanted to post up my own experience with my 8 speed transmission in my 2015 SILVERADO HIGH COUNTRY 6.2L 8 SPEED 8L90

I bought the truck brand new in July 2015. Manufactured date of April 2015. I purchased it from a dealer in NH and they have been great to deal with.

So here is the story-->

July 2015 --> At first the truck was flawless. It shifted butter smooth and on a very rare occasion (once a week maybe) it would clunk slightly when downshifting. It was totally negligible.

***As time went on and the mileage increased it got worse. Here is a list and description of what it was doing once I hit about 3500~ miles. It didn't clunk and act sloppy all the time. HOWEVER, there is a good 65% chance the truck was going to shift poorly.

It clunks (HARD) into lower gears when slowing down/downshifting. This is the biggest issue and has continued to happen up to now.
Taking off from a stop with smooth, consistent acceleration, it has trouble deciding the correct gear and vibrates.
Same scenario as above, the rpm's fluctuate.
It makes clicking noises constantly when shifting. If you manually shift it, you can hear clicks in almost every gear.
I can MAKE it clunk hard if I coast in gear 7 and manually shift it into gear 6. NO RELATION TO AFM/DoD WITH THIS.
For some reason, turning into another road or turning in a slight corner and accelerating will make it downshift and clunk hard.
Going from Park to Reverse either cold or after driving it would slight clunk, then engage a second or two after the initial clunk is heard/felt.

December 2015 --> I took it to my dealer at the 5000 mile oil change/scheduled maintenance and I had the service manager ride with me to hear the clunking. The truck was really acting up that day, and it was clunking like crazy. The service manager said he heard the noises clear as day. He told me the 8 speeds have some clunks, and because they are so new people need to get used to them. He gave me the whole they need to learn and EPA demands greater fuel mileage talk. I disagreed with him and we had a long conversation. I mentioned to him when the truck was new it did not do this.

When we returned to the dealership, this is exactly what he told me: "this is normal operation, we are not going to do anything about this issue"

I asked him to at least check for updates and go over the truck top to toe and check motor mounts, transmission mounts, spring shackles, etc. Just to rule out any possible 'looseness' that could cause the clunks. The work order said they checked for updates and looked the truck over. They found nothing out of place and no updates available.

Around two weeks later, with 7200~ miles on the truck, I was talking to my uncle about the transmission issues and he called his local Chevy dealer on my behalf. The service manager said the 8 speeds have a couple updates available, and to bring my truck up to see if they apply to it. He said the update had really helped a couple 8 speeds they had recently sold. So I drove up to their dealer (an hour in the opposite direction of MY dealer) and they hooked my truck up. I figured MY dealer had done the updates, but there was an available update. They updated it and it really didn't help much. It seemed to make the truck hold a little higher RPM cruising, but I didn't notice anything besides that.

March 2016 --> Just yesterday I dropped my truck off at my purchasing dealership with 9800~ miles. I asked them to do the scheduled maintenance, and look into the transmission one more time. Especially considering it hasn't gotten better, it got worse. I specifically asked them to drop the pan and look at the fluid, valve body, etc. They called me Monday afternoon and told me they took an extensive look at my transmission and they are going to put a new transmission in it. They said after driving it/taking a look that it is "A GM candidate for a new transmission" because of the "symptoms it exhibits"

In 5-8 days the transmission will arrive from Detroit and then they will put in a new transmission.

I will keep you all posted on the results and we will see if over the next 10k miles the new transmission stays smooth.

Dunc · March 1, 2016

Perhaps I should make a trip to talk with my dealer as well since mine too does exactly what you mentioned.

Wnc66 · March 1, 2016

I'm glad to here that Chevy or the dealer actually done something about this.....I've got the same issues maybe worst....the dealer admits there's a problem but tells me there waiting on Chevy to make a call! It's very disappointing too say the least. I'm trying to stay clam.. And let things play out.... But who's addressing this problem... I've called my so called case engineer with Chevy only to get a answering machine... We'll be in touch within 24 hours! 2 weeks later....3 calls...no call back... Nothing! I'm really hoping the new one works! I need to keep some hope... I bought this truck to be my last...way to much money to keep trading and losing! I'll be watching for update.... Thanks Asheville Nc

pm26 · March 2, 2016

And what makes you think that the new transmission will be any better? It will probably work the same as the old one at first and after a while you will experience the same problems. And then what?

Edited March 2, 2016 by pm26

Daryl Z71 · March 2, 2016

And what makes you think that the new transmission will be any better? It will probably work the same as the old one at first and after a while you will experience the same problems. And then what?

Not really any other options at this point, especially when GM is paying for it.

brendan4862 · March 2, 2016

And what makes you think that the new transmission will be any better? It will probably work the same as the old one at first and after a while you will experience the same problems. And then what?

I have thought of this and it's a valid point. Here is how I look at it:

I am giving GM a chance to fix the problem. Out of all the 8 speeds they have manufactured, they can't ALL be bad.

If this doesn't fix it I will ask them to buy it back. If they wont buy it back, then I will trade it in. Lesson learned.

brendan4862 · March 11, 2016

UPDATE 3.11.16

I just got back home after the two hour round trip 'down and back' to the dealer. They didn't get the transmission from GM until Tuesday of this week and they got the transmission swap done on Wednesday.

They said there was an internal failure that causes the transmission to shift hard and not 'mesh' properly. (this is what my service writer told me, so I do not know if this is entirely accurate) The transmission was something GM wanted shipped back to them to investigate further. So that's all the detail I got even though I wanted to know more.

I will be monitoring the way it shifts from here on out closely to see if it has made a big difference. I've only driven it highway thus far and it was smoother than before. I'll keep you all posted.

CounterMeasure · March 11, 2016

They said there was an internal failure that causes the transmission to shift hard and not 'mesh' properly. (this is what my service writer told me, so I do not know if this is entirely accurate) The transmission was something GM wanted shipped back to them to investigate further. So that's all the detail I got even though I wanted to know more.

This is Standard Operating Procedure. When I had my transmission replaced, the dealership was not allowed to open it up. GM wanted it as-is, filter, fluid and all, shipped back to them so they could tear it down and diagnose it. As such, the dealership couldn't tell me much at the time what was wrong, so I believe the same holds true for your dealership at this point. I found out later on that the diagnosis yield no problems, and the issue in question was not related to the transmission at all! The positive side of the experience was I got a new revision of the transmission with gear cut changes and other improvements.

pm26 · March 13, 2016

UPDATE 3.11.16

I just got back home after the two hour round trip 'down and back' to the dealer. They didn't get the transmission from GM until Tuesday of this week and they got the transmission swap done on Wednesday.

They said there was an internal failure that causes the transmission to shift hard and not 'mesh' properly. (this is what my service writer told me, so I do not know if this is entirely accurate) The transmission was something GM wanted shipped back to them to investigate further. So that's all the detail I got even though I wanted to know more.

I will be monitoring the way it shifts from here on out closely to see if it has made a big difference. I've only driven it highway thus far and it was smoother than before. I'll keep you all posted.

I hope this works out for you.

brendan4862 · March 14, 2016

I haven't been able to drive the truck too much since I picked it up. So no update on if it shifts better or not. HOWEVER, when I picked it up I noticed a rather loud exhaust leak. Instead of turning right around and going BACK to the dealer I put it on the lift at home and had to tighten all six (three per side) bolts that hold the catalytic converter/y pipe at the manifold. I can't believe I didn't have a check engine light on the hour drive home. None of the bolts were tight. I think they hand snug them then forgot...

5829BMG · March 14, 2016

Fingers crossed waiting for updates

Sierra Matt · March 14, 2016

Subscribed... I'm having problems with my 8 speed as well. Tranny doesn't engage well especially going from park to reverse and if you give it gas before it's ready, it will hammer into reverse and jerk the whole truck violently. Makes you look

like an idiot driver when it happens. Truck just lurches backwards. Also clunks when stopping or starting from stop. Also clanks between most shifts. This tranny was definitely not ready for prime time. If it had done this when I test drove it.. I would

not have bought the truck.

brendan4862 · March 14, 2016

I just got done driving the truck for about 45 minutes. Mostly around town and here are my findings thus far.

Shifts a lot smoother than before. Sometimes you can't even tell it has shifted. That is a nice plus.

I don't believe the new transmission has fixed my issues though. It had a couple different moments of clunking hard today.

1st: While slowing down at a stop light it went HARD into first.

2nd: While coasting in traffic around 30mph, in V4 mode, I gave it throttle to speed up because traffic was moving again, and it went 'clunk-clunk-clunk-clunk' in quick succession then accelerated. It was switching to V8 mode and trying to get the right gear. It could not figure it out.

3rd: It still takes a while to shift from P to R even when it's warmed up. You really have to give it a few seconds. I have timed it for me. It takes a solid count to three seconds before it engages Reverse.

SO! Here is where I am at right now.

I will be driving the truck for the rest of the week quite frequently and I will monitor its performance for this next week. I am trying to be optimistic about the whole thing, but my patience is starting to wear thin with this entire experience. I cannot say enough good things about my dealer and the service department though. Even though they originally turned me away with my transmission inquiry, they have been trying to work with me & GM to figure this out. No dealer/shop is perfect so I understand when things get missed (my exhaust...)

I'll keep you all posted.

pm26 · March 15, 2016

Maybe disabling the AFM would be a good test to see if the transmission will be less confused and shift better. Personally I would gladly sacrifice 1 or 2 MPG for smooth shifting if it was my truck. Just a thought if shifts continue to be clunky and abrupt. We have a 2013 4X4 crew cab Silverado with the 5.3 engine at work. It has a 6 speed auto transmission, all stock. The AFM works absolutely seamlessly and the transmission shifts perfectly. I cannot get it to act up or shift strange no matter what the traffic conditions, and it never ever slams into gear. Why is it that GM screwed up these new trucks so badly compared to the previous generation? It seems that they went way overboard tuning these trucks for maximum fuel economy.

Edited March 15, 2016 by pm26

brendan4862 · March 19, 2016

UPDATE 3/18/16

I just got home after driving the truck all day. I had to make a round trip to my works warehouse.

I have an appointment on Tuesday to bring the truck back into service. It was clunking all day. Slowing down into first clunk, coasting then throttle application clunk, turning accelerating clunk, you name it. All of which loud enough to hear clearly and jolt the truck. At that time I will be speaking with my salesman and manager about what we can do if it can't be fixed.

It really is a shame. I'm such a fan of GM and they have really let me down. My dealer, thus far, has been excellent.

I'll let you know how it goes.