6 Speed Transmission Clunk Downshift

[Grumpy Bear]

Actually the worst transmission I've ever had was a first year TH700R. That one was so bad that GM was forced to fix it. Second worst was the early Ford AOD.  

[JacobC1983]

Always love the "mine is perfect... blah blah blah..." 

 

It is great that you have a "perfect" one, or more likely just don't notice it because you listen to the radio or are deaf, or just aren't in tune with what your vehicle is doing.

 

I have ridden in great trucks, but I have also ridden in service loaners that are brand new trucks similar to mine that also exhibit the same behaviors mine does.

 

Was curious if there was any new news on the 6 speeds, seems like the 8 speeds have gotten all the attention.

 

Chiming in with the "mine is perfect" crap doesn't help.

 

 

 

To be more specific, I get a clunky, audible downshift from 3->2 and 2->1 at least once every time I drive my vehicle.

 

It doesn't happen often when it is cold, usually when the temp of the trans is 120 degrees and above. As the transmission temp increases, the viscosity of the transmission fluid will change which lead me to hypothesize if changing the transmission fluid to a different type might help, because my truck never clunks right when I start it and get up to below 120 degrees

 

 

Edited March 26, 2018 by JacobC1983

[Mike GMC]

I believe the "mine is fine" posts are in response to the equally useless, "they all suck" posts.

 

That said, have you done a fluid change?  What does the fluid look like?  How is the fluid level?  My theory is that the excessive torque management programming with low line pressure for shifting causes the clutches to slip excessively and wear quickly.  It may even cause them to over heat and get grabby.  This might cause some clunky down shifts.  If yours is still new enough, a fluid change may save it.  This is just my theory and I can't back it up.  Personally, I like a transmission that lets me know when it up shifts.  The stock programming is so mushy, you can't feel it up shifts at all.  This is likely mostly due to desire to keep the drivetrain from shock loads as well as appease the general public that doesn't like to feel anything.

Edited March 26, 2018 by Mike GMC
Fat fingers, little keyboard

[JacobC1983]

I had a 2016 with the 6 speed with similar, but somehow different behavior that I changed the trans fluid at 5000 miles to the same factory fluid.  I had no change in the activity of the transmission.  I was specifically asking about a change to a different brand or full synthetic etc.

[Mike GMC]

I'm not a big fan of factory fluids.  They generally are the bare minimum to meet spec and the cheapest thing they can get.  If I were in your shoes, I'd try Amsoil fluid.  When it's time to change mine, that's what's going in.

[JacobC1983]

Thanks for the advice.  Will give it a shot.

[Grumpy Bear]

45 minutes ago, JacobC1983 said:

Always love the "mine is perfect... blah blah blah..." 

 

It is great that you have a "perfect" one, or more likely just don't notice it because you listen to the radio or are deaf, or just aren't in tune with what your vehicle is doing.

 

Chiming in with the "mine is perfect" crap doesn't help.

It should help unless your just bad mouthing the product in good Troll fashion.  It lets you know there are units out there that function perfectly. It gives proof that it isn't 'normal' that can be shared with your GM tech. What doesn't help is denial and kicking every possible fix offered to the curb off hand.  I rarely listen to anything but the peace and quite in cab and I'm not deaf nor 'out of touch' with my trucks mechanicals. Being dismissive and rude wont get you any help either. That's a pretty good formula for getting yourself ignored when you ask for help. Come to think of it, you have it figured out so well I'm unsure why anyone would comment further. 

[JacobC1983]

I acknowledged that there are good working trucks in my post, you clearly chose to remove them from your response.  

 

Please see yourself out of my thread.

Edited March 27, 2018 by JacobC1983

[wforrest08]

 

Just now, JacobC1983 said:

I acknowledged that there are good working trucks in my post, you clearly chose to remove them from your response.  

 

Please see see yourself out of my thread.

Some people on this forum find it necessary to comment on every thread posted even if they don’t have anything to bring to the conversation... 

[JacobC1983]

Apparently so!

 

Since I have had a 2016 and 2017 GMC Sierra SLT with the 6 speeds, I have come to a few interesting conclusions.  All 6 speed (even though the same truck in an assembly line) are not created equal.  My 2016 had a clunk downshifting but it was never as pronounced as my 2017.  However, my 2016 had a weird shift from 2nd to third and my 2017 never has that issue.

 

I always feel the v4 /v8 transition in both trucks though 

[Mike GMC]

Can you explain more about what you mean by clunky?  Are you referring to an actual clunk noise, or are you referring to jerky, slow awkward shift that throw you forward before it throws you back?

[JacobC1983]

Actual clunk noise. Audible over the radio. 

[Mike GMC]

You probably have done this, but it might be worth getting underneath and checking the entire drivetrain for loose bolts.  I'd also check the U joints.  If you can get it up on 4 stands, you might even be able to run it and listen to see if you can pinpoint where the noise comes from.

[Ali Luz]

I have a 2014 with 92k miles on it and GMC just put in a remanufactured transmission covered under warranty. At 89k miles it was slipping so bad. Valves and the torque converter were replaced. But then it had new issues so they got approval to swap out the whole tranny. Hoping some things are better. The 2019 canyon v6 8 speed I’ve been driving has been much nicer as far as shifting goes. 

[NorthEast]

Since it's first month on the road, my 6 speed has clunked, slammed into gear, hesitated, jerked, and popped so hard from the rear end that it felt like someone rear ended me multiple times.  

It happens the most during normal suburban driving.  

 

GM gave me a TSB and explained that it is due to the gears moving at different speeds.  

 

Apparently GM is the only manufacturer who experiences design hardships with confusing, spinning parts.  

 

After reading some of the good experience posts, I've decided to keep pushing the issue before I run out of the powertrain warranty (currently at 20k)