8l90 Reverse only clunk

11bravoZ71 · December 13, 2021

Tried to upload video but to big I guess.

I was wondering if it’s normal for 2019+ Silverado 8l90’s to have a clunk/bang going in to reverse from park and also from any gear to reverse for that matter

I saw the drive shaft that connects to the transfer case when testing and it moves shakes violently when I go reverse only.

Truck has almost 60k miles. And has had the atf changed. Always thought this was normal. Until my inlaw said wth is wrong with your truck.

my in laws 6 speed older Escalade doesn’t do this all at always shift like butter going into reverse.
could it be a characteristic of the 8l90’s?

I attached a photo of the shaft that shakes like crazy and the transfer case. Only when I go into reverse. Has done this since brand new. Just always thought it was normal. Maybe the transfer case is loose or idk. Worried this tranny can go after warranty. If this isn’t normal and the dealer says it’s normal might potentially trade in.

Does your 8l90 have a heavy loud bang going into reverse? Cold or warm

Edited December 13, 2021 by 11bravoZ71
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AD80 · December 14, 2021

My 2019 8 speed. does the exact thing. Only in reverse it slams into gear. After I drive it a few miles it doesn’t do it. You can let it sit and warm up all you want but that doesn’t help, it has to be driven a while for it not to fo it. I’ve gotten in the habit of backing in to the garage or parking spot after driving so it doesn’t do it, that way after it cools down I can pull out in forward to avoid the hard clunk. Carried it to the dealer a while back but of course when I get here it was warm from the drive and didn’t do it. Of course they said it was normal. It can’t be good for the trans, this isn’t your normal jerk, it’s a hard clunk like gears slamming together, shakes the whole truck. As far as driving, it shifts smooth. No problems there.

11bravoZ71 · December 18, 2021

On 12/13/2021 at 7:02 PM, AD80 said:

My 2019 8 speed. does the exact thing. Only in reverse it slams into gear. After I drive it a few miles it doesn’t do it. You can let it sit and warm up all you want but that doesn’t help, it has to be driven a while for it not to fo it. I’ve gotten in the habit of backing in to the garage or parking spot after driving so it doesn’t do it, that way after it cools down I can pull out in forward to avoid the hard clunk. Carried it to the dealer a while back but of course when I get here it was warm from the drive and didn’t do it. Of course they said it was normal. It can’t be good for the trans, this isn’t your normal jerk, it’s a hard clunk like gears slamming together, shakes the whole truck. As far as driving, it shifts smooth. No problems there.

Thanks for the reply. Yup so we seem to have the same issue. Expect yours doesn’t do it anymore when you drive it a few miles at least. I think yours sounds like the “delayed engagement”
Because that issues explains that it only does it on the initial reverse then goes away…. And comes back if left overnight etc…probably a good idea to leave it at the dealer over night so they can see the issue on a cold start.

In my case The only time mine doesn’t clunk/slam is on a cold start when the RPMS are over 500 if I shift to reverse quickly it won’t do it at all. everything is quite. Once the normal idle of 500 comes in it’ll clunk 24/7 all day everyday into reverse smh.

And yes when it’s slams it feels like something drops hard down underneath you… one solid loud bang. it can’t be good but I don’t get why some 8l90 are smooth as hell. Must be a software issue. Or idk my transfer case because all that moves and shakes hard on the clunk… it shifts just fine other then that.

Going to try and get it to the dealer before warranty is gone. I’m at 55k

11bravoZ71 · December 21, 2021

Got the dealer to take a look. And they said they also saw a shutter due to the fluid and also confirmed my reverse clunk issue. According to their computer graph they can see the shutter. They did the Mobil 1 blue label flush. It did not fix the reverse clunk/bang into gear.

Edited January 19, 2022 by 11bravoZ71

11bravoZ71 · January 19, 2022

So anybody have this jolt/clunk/bang with a small delay going into reverse? Along with a rattle on their drivetrain near the transfer case.. . Or does your 8l90 shift like butter going into reverse??? With no noise from underneath. Is it supposed to?….
I did try it in 4lo and 4hi and the clunk is actually a lot less going into reverse not sure how.

if you had this issue what was the fix? It happens every single time I go into reverse unless the RPMS are high on a cold start the drivetrain feels tight. Then at idle it gets sloppy again.

my in laws 6l80 shifts in to reverse like butter you don’t feel any noise or delay or movement in the drivetrain.

Taking it back for the dealer I have 2k miles left on my warranty. Last ditch effort if they say it’s operating as designed or cannot fix it otherwise. Might trade this in for a custom trail boss with the 6 speed idk…. unfortunately don’t want to risk this failing after warranty… things like this make me want a more base trim for the long run… the less tech and less gears the less complexity.

Edited January 19, 2022 by 11bravoZ71

AD80 · January 19, 2022

As I said above, mine goes away after driving a few miles, but when driven little or cold it does help when the rpm is up, so I just put it in nutreal, hold the brake, run it up to about 1000 then go to reverse real fast. and it gets smoother. Their seems to be a sweet spot. If I were you, I’d just do that when you back up until you figure it out. I have plenty of warranty left and I plan on trading it when the new 2022s comes out, so I’m not too worried about it, but if you plan on keeping yours a while, then I would definitely have the dealer fix it before warranty is up.

Also if they try to say it’s normal (like they did me), I would let them feel yours, then go get in another one on the lot that shifts smooth , so they can see the difference and that it’s not normal.

Edited January 19, 2022 by AD80

M1ck3y · January 22, 2022

The trans fluid exchange only applies to k2's; T1's should have come with that fluid from the factory. Imo I would try another dealership and see if they can't diagnose the issue for you.

Edited January 22, 2022 by M1ck3y

Silverado4x4 · January 22, 2022

6 minutes ago, M1ck3y said:

The trans fluid exchange only applies to k2's; T1's should have come with that fluid from the factory. Imo I would try another dealership and see if they can't diagnose the issue for you.

No it also applies to the T1 built in 2018 till something like March of 2019 for the fluid exchange. I had mine done in like August of 2019 for the shutter and it's been fine since mine was built in November of 2018.

M1ck3y · January 22, 2022

12 minutes ago, Silverado4x4 said:

No it also applies to the T1 built in 2018 till something like March of 2019 for the fluid exchange. I had mine done in like August of 2019 for the shutter and it's been fine since mine was built in November of 2018.

My mistake. They must have ended up including that year after the original tsb's were issued. A T1 is considered a 2019 model regardless of build date.

https://gmauthority.com/blog/2019/08/tsb-seems-to-fix-8-speed-automatic-gm-transmission-problems/

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163890-9999.pdf

Edited January 22, 2022 by M1ck3y

11bravoZ71 · January 25, 2022

Took the truck in last week to continue the diagnoses on the reverse clunk. But the transmission techs were both out due to Covid. Service adviser said they should be back this week. Then I’ll go back. So far this dealer has been good going to let them check if they can’t then I’ll try another dealer. I have 2k miles left in my power train warranty. But the service adviser said he noted my issues in case I go over my warranty.

Michel vidana · August 1, 2022

My 18 with the 8 speed does the same thing but only when hot. When cold shifts like butter. Was at dealership for 2 weeks and they took transfer case apart. Took a look at yokes and they said no issue. Some do it. Some don't. Who knows anymore

GMCustomerService · August 5, 2022

On 8/1/2022 at 5:27 AM, Michel vidana said:

My 18 with the 8 speed does the same thing but only when hot. When cold shifts like butter. Was at dealership for 2 weeks and they took transfer case apart. Took a look at yokes and they said no issue. Some do it. Some don't. Who knows anymore

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