8 speed automatic problems and B pillar rattle

Waterskier98 · September 24, 2019

I'm trying to see if anyone has a problem with delayed shift engagement with their 8 speed automatic? I have a 2018 GMC Colorado 4x4 V6 crew cab, which I purchased brand new. Since 500 miles the vehicle has had a 5 to 8 second delay in shifting from park to drive (or to reverse), usually after sitting for several hours (example: overnight, in my garage). The vehicle now has 7000 miles and the problem is getting worse. I have taken it in FOUR TIMES for this issue, and each dealer alleges they "can't duplicate" the problem, or allege that it's "normal." The transmission, after being shifted into drive or reverse feels like it's in neutral. It then gradually starts moving (feels like fluid pressure gradually builds up, then the vehicle will move).

Question: does your 8 speed automatic have delayed shift engagement? If so, has GM fixed the problem with your truck? I've had no other issues with the transmission.

Second question, I have a constant B pillar rattle (sounds like two wires inside the B pillar, around the seat belt - at head/ear level). I have made three visits to GM dealers for this problem. They have only made the problem worse - it's now almost constant rattling, even on smooth roads, and VERY annoying. Anyone successful in getting this fixed? And if so, what was the fix? Due to GM's inability to fix the problem I even removed the B pillar plastic myself, but could not find any obvious source for the rattle.Thank you

Edited September 24, 2019 by Waterskier98

Bob Miller · September 24, 2019

Hi Waterskier - there's a long thread about the B Pillar tick going on over here:

There's a lot of guys on that thread with a lot of ideas of what it may be that's making the noise on their various trucks. It's been happening to me but only in the mornings on my way to work when its about 75-85 (or so) degrees outside. Once it warms up during the day it goes away. If its a morning that is gray and rainy or the previous day's temperature didn't get very hot then the noise isn't there (for me at least).

Incidentally my biggest heartache has been my passenger seat. It was rattling like crazy and I finally got the dealer to fix it about 2 weeks ago (they did something to the frame inside the seat). It was dead quiet until yesterday, now its rattling like crazy again and I'm about to bring it back tomorrow.

For the pillar I'm thinking that I'm going to take the b pillar trim back off (I've had it off before looking around and like you couldn't figure out anything) and I may just get some real good dynamat or some other sound absorbing material and just place it all inside there. I've even been toying with having a stereo shop or other such type of place do it. If its only $150 or $200 it may be worth not having to take it back to the dealer 20 times .