2015 Sierra, 6-speed transmission clunk

RahinMVA · May 18, 2020

Hi all,

I have a 2015 GMC Sierra, 51K miles, and my transmission acts funny:

- rough shift from 2 to 3 when starting from a dead stop

- occasional "clunk" when decelerating from highway speed (foot off the accelerator)

- when in stop-and-go traffic there is strange / clunky shifting between gears, occasional random "clunks", almost like it can't figure out what gear it wants to be in

Any thoughts on these issues? Could it be related to the AFM / DoD? Could my transmission be going bad already with just 51K miles? Thoughts on how to correct this?

Any input would be appreciated. Thanks!

Rich

Edited May 18, 2020 by RahinMVA

Lsgun1 · May 18, 2020

Sounds like pretty normal operation. The AFM definitely seems to change how they shift even though it's not supposed to. Have you checked the fluid level and condition? You are at the miles it should be changed.

RahinMVA · May 18, 2020

3 hours ago, Lsgun1 said:

Have you checked the fluid level and condition? You are at the miles it should be changed.

Yes, I had the fluid & filter changed at about 48K, per the owners' manual recommendation. Symptoms were the same before and after the fluid change.

It is hard to hear that this might be "normal." My only other experience is my old truck - a 2000 Silverado that had 185K miles on it when I bought it. Other than the typical clunk when shifting out of Park, it was very smooth.

Grumpy Bear · May 18, 2020

Is this something it just started doing or has it been like this from day one?

14TopazZ71 · May 18, 2020

Can you pop your air filter box open and see if there is oil in the airbox? Mine had the same transmission issues, the MAF was coated in oil.

RahinMVA · May 18, 2020

54 minutes ago, Grumpy Bear said:

Is this something it just started doing or has it been like this from day one?

No, not at all from day 1; but it also wasn't anything sudden. It was a subtle ramp up over maybe the last 18 months or so to the point that I now notice the rough shift from 2 to 3 all the time; and the odd clunks described in my original post are now obvious.

49 minutes ago, 14TopazZ71 said:

Can you pop your air filter box open and see if there is oil in the airbox? Mine had the same transmission issues, the MAF was coated in oil.

Just looked. No sign of oil.

Also, FWIW, this truck has only been serviced at GM dealers.

Edited May 18, 2020 by RahinMVA

BlancoSilverado · May 18, 2020

1 hour ago, 14TopazZ71 said:

Can you pop your air filter box open and see if there is oil in the airbox? Mine had the same transmission issues, the MAF was coated in oil.

14Topaz has a good point. you might want to buy a $5 spray bottle of MAP senor cleaner and see what it does.

Grumpy Bear · May 18, 2020

1 hour ago, RahinMVA said:

No, not at all from day 1; but it also wasn't anything sudden. It was a subtle ramp up over maybe the last 18 months or so to the point that I now notice the rough shift from 2 to 3 all the time; and the odd clunks described in my original post are now obvious.

Just looked. No sign of oil.

Also, FWIW, this truck has only been serviced at GM dealers.

Clunk is sound that 'loose' devices make. It's slack take up. As a device wears clearance increases and noise/feel happens. While it may sound odd for this to happen at such low miles it may have started during manufacture that parts were at the top of their specs. Some things easy or at least cheaper to check. Differential back lash. There is a maximum spec for this. A GM dealer can measure this. Front driveshaft yoke splines need heavy grease. Universal joint wear. Just some ideas to add to cleaning the MAP. Let's not worry about the big things until the little ones have been looked at.

flyingfool · May 21, 2020

check this out, no.1 reason to delete the trans t-stat.. minimize heat distortion to the plastics in the valve system

Edited May 21, 2020 by flyingfool

Malibu SS · May 22, 2020

Buy a tuner. Delete the Active Fuel Management....Raise the shift points by about 300 RPM.......and increase the shift firmness by 25% That should fix ya' right up....

Og Goldie · June 4, 2020

yea im having the same clunkness but only at start form a complete stop like at a stop light. Dealer regreased driveshaft plines then it stopped, but after installed a 2.25" front leveling kit the clunk was back. i now have an diablo 87octane tune, afm off, trans point at 15% & still doing it. so at this point im completely convinced chevy dropped the ball with the drivetrain issues

lmcdonald10 · June 8, 2020

On 5/17/2020 at 8:42 PM, RahinMVA said:

Hi all,

I have a 2015 GMC Sierra, 51K miles, and my transmission acts funny:

- rough shift from 2 to 3 when starting from a dead stop

- occasional "clunk" when decelerating from highway speed (foot off the accelerator)

- when in stop-and-go traffic there is strange / clunky shifting between gears, occasional random "clunks", almost like it can't figure out what gear it wants to be in

Any thoughts on these issues? Could it be related to the AFM / DoD? Could my transmission be going bad already with just 51K miles? Thoughts on how to correct this?

Any input would be appreciated. Thanks!

Rich

It is not normal. My 2017 Silverado with 6 speed does the same thing. I just had the transmission rebuilt and it’s doing the same thing. I’m thinking maybe TCM issues? I don’t know but I’m to the point of selling my truck over this

Podcastville · August 23, 2021

This was happening to my 2015 gmc sierra. The occasional clunk turned into more frequent clunks, especially when under load at low rpms. Turns out I need a new transmission at 51k miles. Well that's what the dealership says atleast.