2020/2021 8 speed problems

[dgstarr63]

Does anyone else have hard shifts into 1st gear when coming to a stop. My dealer says newer trucks don't have a problem. They will have a tech check it out tomorrow, but I am concerned that they won't fix it. My truck is a 2021 Silverado 5.3, 8L90 transmission. I don't see why a fluid change will correct the problem when the truck was delivered with the latest fluid.

Edited April 4, 2021 by dgstarr63
added the year of vehicle

[Adamace1]

I have a 21 5.3 crew cab standard bed. It has the 8 speed. The only thing it does that's not normal, is every 10 days or so it will downshift into first gear 6 to 7 mph hard and kinda jerk the truck. But the next 9 or so days it's perfect. Last time it did it it was only for half an day. I got 4,300 miles. I would have maybe took to dealer buts it's rare, and I know if I tool it there it would not do it when I brought it there.  

 

My 2017 impala did the same thing but not quite are hard. Maybe the rear drive and long drive shift makes it worse.

 

I used to drive ford 150 for work my last two a 2018 and 2015 both did a hard downshift into first with a loud clunk from the drives haft rear end area, was really bad in sport mode.

 

I'm not very worried about it myself.

Edited April 4, 2021 by Adamace1

[Ultimate 2022]

There have been numerous threads on this. It’s a very very common issue. Dealer will swap fluid and reprogram and it’ll help. It’ll also help to warm up the truck before driving and to come to a complete stop before shifting from R to D.

 

I believe there are three or four threads posted regarding this topic in the last week or so, you might check those out, too.

Edited April 4, 2021 by 2020SilveradoCC

[Adamace1]

41 minutes ago, 2020SilveradoCC said:

There have been numerous threads on this. It’s a very very common issue. Dealer will swap fluid and reprogram and it’ll help. It’ll also help to warm up the truck before driving and to come to a complete stop before shifting from R to D.

 

I believe there are three or four threads posted regarding this topic in the last week or so, you might check those out, too.

I thought the gm service bulletins are for tourqe converter vibrations, and hard up shifts on older models. And to replace older fluid with the newer type. A 21 comes with the new fluid and I have seen several people on this site say their dealer will not change the fluid on the newer transmission because they don't have the shudder/ upshift problems. 

 

Also my truck downshift perfect on cold fluid the only time it will downshift hard is on fully warmed up fluid.

Edited April 4, 2021 by Adamace1

[Diamond817]

Can't fix a design flaw. GM admitted it's a design flaw in the ongoing class action lawsuit over the 8spd. 

 

GM is actually arguing they shouldn't have to warranty the the transmissions because it's a design flaw and not a warrantable workmanship issue. Seriously, that's their defense.

Edited April 6, 2021 by Diamond817

[redwngr]

Maybe??

 

This is for 2021's.

As others posted, 2021's will already have the newer fluid.

 

https://gm-techlink.com/?p=14564

Twisted Transmission Cooler Line

March 30, 2021

A harsh shift, shudder, surge or stall condition may be present on some 2021 Silverado, Tahoe, Suburban, Sierra, Yukon, and Escalade models equipped with the 6L80 or 6L90 6-speed automatic transmission (RPOs MYC, MYD), 8L90 8-speed automatic transmission (RPO MQE), or 10L80 or 10L1000 10-speed automatic transmission (RPOs MQC, MQB, MGM, MGU) and with low mileage. These conditions may be caused by a twisted transmission cooler line. (Fig. 11)

 

Fig. 11

 

When checking for a twisted cooler line, it may be necessary to remove the underbody panels in order to clearly see all the lines.

If a twisted cooler line is found, disconnect the cooler line from the transmission auxiliary cooler and untwist it. Reconnect the cooler line if the rubber is not deformed or misshapen or there are not any other issues with the line. If the cooler line is damaged or deformed from being twisted, it should be replaced.

Check the transmission fluid level following the procedures in the appropriate Service Information and add fluid if needed.