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2007 GMC Acadia SLT FWD; 2008 GMC Acadia SLT AWD
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Discussion Starter · #1 ·
This is my 07 SLT. I was having the well known shudder at low rmp ~ 1200-1500. It has gotten worse lately. I have read lots of post here on the issue and have tried many different things including adding Lubegard shudder fix that did not make a difference.
The transmission has been replaced and rebuilt by me with help from this forum (in this post 07 transmission shifting troubles | GMC Acadia Forum ). That did not make a difference to the shudder.
I can rule out engine misfire issues as the spark plugs and coil are less than 20K kms, all the coils fire when I tested them.

As all indications pointed to the torque converter, I decided to it take out and replace it. Took it to a local transmission shop that rebuilds torque converters in-house. They did not have one in stock so they opted to rebuild mine.
I received a call today that the torque converter was fine and they only cleaned it as there wasn't anything to rebuild. Although I had to pay the full cost of the rebuild since the converter had to be cut open before they could determine it didn't really need a rebuild.

Now my dilemma is whether to trust the shop (I have no reason not to trust them) and reuse the cleaned torque converter or buy another.
I currently have the engine and transmission out sitting in the garage so I can check or replace anything that could be a culprit besides the torque converter.
Any ideas on what else I should check or replace that will help with the shudder whiles everything is out and accessible?
 

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Not meaning to be pessimistic, but at this time, many parts are difficult to get for rebuilding anything let alone and entire end item part.
So i have to wonder if they just found that parts are not available and so just cleaned it.

Maybe see what availability for the entire TCC is online or elsewhere?
 

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Not meaning to be pessimistic, but at this time, many parts are difficult to get for rebuilding anything let alone and entire end item part.
So i have to wonder if they just found that parts are not available and so just cleaned it.

Maybe see what availability for the entire TCC is online or elsewhere?
I tend to agree. Shudder almost always points to the converter. I might check with another transmission shop for a rebuilt one.
 

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2007 GMC Acadia SLT FWD; 2008 GMC Acadia SLT AWD
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Discussion Starter · #4 ·
Thanks JayTee and Divotdog for the input.
I was also "1000% sure" the torque converter should be the issue given all the other likely suspects have already been taken care of.
What baffles me is if the converter was bad and they couldn't rebuild it, they could have easily told me they rebuilt it (although in reality they did not) as there is no way of telling without cutting the converter open.

I will shop around and see what I can find locally.
If prices aren't crazy expensive I will just get another rebuilt unit.
Too bad the torque converter replacement involves dropping the engine and transmission. I would have tested a new one and then if the issue goes away, put back the cleaned one just for knowledge.
Interestingly, I have a used torque converter that came with the used transmission I bought sitting in the garage. I did not use it because the oil in it was too dark and thought it might be too risky to use.
 

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Good luck with your investigation and choice. Repairs. . . always do not seem so clear cut these days.
 

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Discussion Starter · #6 ·
Just an update.
I ended up getting a new rebuilt torque converter and used that.
It appears the transmission shop was right about my torque converter not being the issue.
After test driving the shudder was still present exactly as before. Test drove it for about 180 km.

I had read about the transmission adapts reset after a transmission change or rebuild. So I had that done.
This smooth out most of the shudder as I kept driving although it is still noticeable when speed is about 60km/h, albeit less intense than before. I will keep driving to see if the adaptive learn continue to improve the shifts and stop the shudder so it begins to drive as smooth as our 2008 Acadia.

I noticed after the reset that the transmission jerks once in a while as if it isn't sure what gear to shift to. Shifts are generally smooth most of the time. Also, the tech bounces around a lot more after the reset but my guess is this is a symptom of the adaptive learning.

Has anyone had their transmission adapt reset and can share what their experience?
 

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Thanks for the update. Have not had any experience in these earlier Acadia 6 speeds. I can say, though, that our 2019 6 speed is not near as smooth shifting as basically the same transmission we had in out 2015 Equinox LTZ 3.6L.

I can say that in our 2019, it doesn't seem to like to be "babied" or allowed to bog down. The shifting is much smoother with the tachometer at the 2,200 to 2,500 RPM for shifting. In that RPM range, shifts occur more as expected . Letting the Acadia shift below those RPMs seems to inspire uneven pull and a lurching behavior.
So I find that pressing the gas pedal to attain about 2,200 RPM or so produces a better driving experience.

Unlike other GM vehicles we've had with either the 6T70 or 6T75 transmission. I do not think the earlier versions of this transmission had a clutch aspect to the lock up torque converter. In the earlier versions, the lock up just occurred with no slippage at about 42 MPH or so. That doesn't seem to be true for all applications across the GM models however.
At least. . . . that seems to be my observation. I could be wrong, . .
 

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Discussion Starter · #8 ·
I can say that in our 2019, it doesn't seem to like to be "babied" or allowed to bog down. The shifting is much smoother with the tachometer at the 2,500 to 2,700 RPM for shifting. In that RPM range, shifts occur more as expected . Letting the Acadia shift below those RPMs seems to inspire uneven pull and a lurching behavior.
So I find that pressing the gas pedal to attain 2,500 RPM or so produces a better driving experience.
This is exactly what is happening. The jerking I mentioned only happens when gear shifts occurs at or below 2000rpm, which is mostly during city driving.
I guess having the 2008 be as smooth as butter had me expecting all Acadias to be that smooth :)

Haven't had a chance to driver more yet as I had to take down the tail gate to get some rust issues fixed.
I will try and update this thread again when I have added more kms to the vehicle.
 

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Came across this thread regarding the accelerator position sensor that could be the culprit. Haven't had the chance to replace mine yet to see if it is the root cause.

 
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