8spd issues

CamaroVetteGuy · January 10, 2021

On 1/1/2021 at 12:48 PM, UGADawgs said:

To describe it, it is like the truck goes to speed up and is then slightly being pulled back by tug rope and then it releases and it lunges and drives normally.

I had a 17 Silverado with the 6 speed that did this.

Swofford · January 10, 2021

well, I have the truck back and I don't see any reason to back out (at least at this time).

The issue with the transmission hard downshift and a temp high-idle situation were caused when the dealership replaced a valve body on the transmission, when they found a slightly out of spec one during the GM pre-owned certification process (according to them). and apparently as part of the replacement, a software update to the TCM software is made. In this case, the software update did not complete successfully, causing the issue. Once the update was applied and completed successfully, the transmission is as smooth as anything I have ever driven. Time will only tell if this is the total resolution for the future.

Additionally, the SRS messages and airbag light issue was a clock spring issue. They replaced the clock spring and no more message....

flyingfool · January 10, 2021

the software tune is the main issue in all the trans. they need reprogramming, its designed around highest MPG and maintaining low emmisions

SilveradoRST · January 10, 2021

The hard shift when cold is a known thing for the 8 speed. Just found out now myself. Seems like it is nothing to worry about.

https://static.nhtsa.gov/odi/tsbs/2019/MC-10168176-9999.pdf

flyingfool · January 10, 2021

i recommend buying the GM transmission tuning book at the Tuning school,

Phantom 4D · February 8, 2022

Cold hard shift seems to be an issue for sure. My truck had been sitting since Friday 2/4. The temps dropped at night in the low 20s. Monday 2/7 I got in to go run some errands. Shift from first to second was so hard it threw me forward. Second to third was hard but not as much as 1-2. the remaining shifts were a bit rough. Had the familiar hard downshift coming to a stop the rest of the day. The fluid was change at the last service due to shifting issues. Didn't help. Aggravating.