2018 sierra Denali weird vibration

hackitz · September 2, 2020

hey all,

so i have a 2018 denali, bought new. truck came with the 6.2l.

so truck seems to vibrate/ shutter, shake when it's changing gears and steady at 100 km an hour.

i took it into the dealer and they said my tranny fluid was burnt and changed it. it's now back to smooth riding.

my question is two fold, has anyone had issue with the tranny fluid?

next i had a pedal commander installed and left it on the sport+ setting, could that have caused the tranny fluid to go bad? i'm not sure i want to install the pedal commander back in the truck until i know why the fluid went bad so quick.

oh, i've had the truck for 1 and half years and it's only got 55000 km on it.

thanks

silveradosid · September 3, 2020

pedal commander had nothing to do with it, your 8 speed transmission needed the updated fluid to correct the problems you described

Lsgun1 · September 3, 2020

Very common problem with the 8 speed. Use your pedal commander if you want, it won't hurt the new fluid and it isn't what caused the old fluid to suck.

hackitz · September 3, 2020

ok thanks.

i did notice sometimes the tranny was the weak link with the pedal commander installed. engine would rev but took a second for the truck to move and with a slight clunk from the tranny/drive shaft? i'd be off.

i'll put it back on and keep an eye on the fluid.

i did remove it before i took it in just incase the dealer said it caused the issue.

also was there an issue with the type of fluid gm used? or does it need to be replaced every 50 km or so?

HOGNATION_64 · September 3, 2020

I just had my 2018 Chevrolet Silverado Crew Cab LTZ 4x4 in for the same thing. They flushed my fluid and put in a Mobile HP Blue Label fluid and I have put about 500 miles on since and no problems. I'm just always in the back of my mind thinking is that the shutter shake again even though it just might be the road.

hackitz · September 3, 2020

33 minutes ago, HOGNATION_64 said:

I just had my 2018 Chevrolet Silverado Crew Cab LTZ 4x4 in for the same thing. They flushed my fluid and put in a Mobile HP Blue Label fluid and I have put about 500 miles on since and no problems. I'm just always in the back of my mind thinking is that the shutter shake again even though it just might be the road.

man aint that the truth, my 2014 had the shake.

dwchapmanjr · October 4, 2020

My 2015 had the shake about a year in and it took about 2 years for them to find a permanent fix with the new Mobil HP fluid. I went through quite a few flushes and even a TCC replacement but the Mobil HP flush I had done early 2019 fixed it. The issue with the other fluids is that moisture builds up and causes increased friction.

You don't mention your mileage but in my maintenance schedule it indicates 45k miles for fluid and filter change which I imagine for a 2018 you're probably close to that.