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Discussion Starter · #1 ·
Hello Everyone,

New to the forum here, happy to be a part of it!

I have a 2017 Acadia Denali with ~133,000 miles. About two months ago I noticed a jerking/shuddering at highway speeds, generally between 50-65mph. This only happens under light acceleration or cruising up a slight incline. If I let off the gas or accelerate harder it goes away. There are no codes/CEL that have been thrown. I can see that the RPMs jump a bit between 1500 and 1800 and the speedo is jumping a few MPH up and down while happening.

The issue feels like a rapid power surge and fade. Since it started two months ago it has gotten progressively worse and seems to happen at times during even lower speeds. Still no codes being thrown.

I took it to my mechanic who also wasnt able to diagnose it. He suggested it could be a number of things(coils, trans, failing sensor) but didnt want to start throwing money at it until a code was thrown.

Im tired of waiting and would like to diagnose!

Any thoughts? Appreciate the help!
 

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Lock up TC locking and unlocking? Shifting up and down?
 

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How many kms since last trans oil change? I've heard of radiator cracking internally and swapping trans oil with coolant on older yukons, and newer blazers.

You might be able to dip a shop towel in your trans filler hole and see if it's murky oil? It's right side of th engine and tucked under some stuff. But I can reach mine on 2021
 

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Discussion Starter · #5 ·
How many kms since last trans oil change? I've heard of radiator cracking internally and swapping trans oil with coolant on older yukons, and newer blazers.

You might be able to dip a shop towel in your trans filler hole and see if it's murky oil? It's right side of th engine and tucked under some stuff. But I can reach mine on 2021
Last trans oil change was about 25k miles ago (at 105k). Trans shop guy said it was dirty but nothing alarming.

Yes I found filler hole, planning on putting lubegard shudder fix in to see if that helps. Will also dip a rag to see how oil looks.

Also on a second round of injector cleaner.
 

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Discussion Starter · #7 ·
Last trans oil change was about 25k miles ago (at 105k). Trans shop guy said it was dirty but nothing alarming.

Yes I found filler hole, planning on putting lubegard shudder fix in to see if that helps. Will also dip a rag to see how oil looks.

Also on a second round of injector cleaner.
OK so I just checked trans fluid. I wouldnt call it murky was more of a light brown/reddish.

Also put a 2oz tube of lubegard shudder fix in. I am going to log about 150mi for work today.

I’ll also try tow and sport mode as I usually run in 2 or AWD.
I will keep ya’ll posted on how it runs later!
 

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OK so I just checked trans fluid. I wouldnt call it murky was more of a light brown/reddish.
Also, make sure the fluid level is within range (use the proper method for checking fluid level). Too much or too little fluid can make the transmission shift 'funny.'
 

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Lock up TC locking and unlocking? Shifting up and down?
The 8 and 10 speed transmissions had TCC slipping or shuddering at certain speeds.
Apparently some owners with 6 speeds also now are seeing it.

I'm thinking whoever did the transmission control software wasn't given enough time to get it refined.
 
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Proper method of checking Fluid level? Isn't this to hoist it perfectly level and then unscrew a plug while car is running?
 

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... Isn't this to hoist it perfectly level and then unscrew a plug while car is running?
I believe that applies to the 9-speed transmission. The 2017 Acadia has a 6-speed. The 2017 owners manual makes reference to a dipstick.
 

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Discussion Starter · #13 · (Edited)
Ok so somewhat of an update!

First off, thanks for all the replies.

Trans was serviced at ~100,000 miles @divotdug Also, yes there is a dipstick, its below and to the left of the battery. It is more of a cap with a dipstick attached to it than what you would see as an engine oil dipstick.

The shudder mostly goes away in sport mode. In tow mode it completely goes away. @Erickson6111

I read that the lubegard shudder fix takes ~25 miles to start working and that's about what happened. About an hour into my workday yesterday I noticed that the issue was reducing a little at a time. I'd say that today (day two after lubegard) its 50-75% better. Still getting the vibration/shuddering mainly while accelerating on an incline but less severe and frequent.

I called my local transmission mechanic and explained the situation. He is going to hop in the car with me on Friday AM and have me replicate the issue while his scanner is plugged in. He gave me a little insight into what his suspicions are. Basically these tranny's start to lose the ability to hold enough pressure to lock the torque converter clutch as they age. He said when you switch to sport or tow mode the system automatically increases the pressures and will mask the problem.

If that is indeed the issue he listed a few options with different price points to fix (replace with remanufactured, rebuild, replace with used). I'll have to see what he quotes for each before I make a decision. Any future advice on which route to take will be appreciated. Acadia is in great shape otherwise!

The kicker is I made my last car payment on 8/17/21, was excited for no more car payments and then this all popped up within a few weeks. That's the brakes!

I'll have more info after my ride Friday morning, keep you posted!
 

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Hello Everyone,

New to the forum here, happy to be a part of it!

I have a 2017 Acadia Denali with ~133,000 miles. About two months ago I noticed a jerking/shuddering at highway speeds, generally between 50-65mph. This only happens under light acceleration or cruising up a slight incline. If I let off the gas or accelerate harder it goes away. There are no codes/CEL that have been thrown. I can see that the RPMs jump a bit between 1500 and 1800 and the speedo is jumping a few MPH up and down while happening.

The issue feels like a rapid power surge and fade. Since it started two months ago it has gotten progressively worse and seems to happen at times during even lower speeds. Still no codes being thrown.

I took it to my mechanic who also wasnt able to diagnose it. He suggested it could be a number of things(coils, trans, failing sensor) but didnt want to start throwing money at it until a code was thrown.

Im tired of waiting and would like to diagnose!

Any thoughts? Appreciate the help!
My bet is failed torque converter. They are tiny 12 inch diameter and for horsepower / weight of the car way too small.

Same issue with my 2012 Acadia. I put in a new one and the issue went away. Unfortunately the torque converter sheds debris and may kill the transmission too.
 

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Discussion Starter · #15 ·
Just got back from trans shop.

Mechanic is relatively certain that the trans control valve body is worn out and in turn is not holding enough pressure to lock the torque converter clutch. Once that starts happening the clutch itself begins to wear out as it starts to slip more and more.

He gave me two options for repair.

First is simply replace the valve body. Its the least expensive (~$1700) and should work fine as long as the clutch isn't too worn out.

Second is a more comprehensive repair and runs about $3500. He drops transmission and replaces valve body but also checks out Torque converter clutch. If its worn out, which he suspects it is given that this issue is two months old, he will replace that as well. I also have a small leak at transfer case where it meets trans (old issue ive been keeping an eye on) that would be fixed by going with this route.

I am leaning toward the second option as I don't want to mess around any more with this. Let me know if ya'll have any input on this!

Dropping Acadia off for repairs on 10/25. Will be sure to update the thread afterward as nothing grinds my gears more than when people don't post what final solution was!
 

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Just got back from trans shop.

Mechanic is relatively certain that the trans control valve body is worn out and in turn is not holding enough pressure to lock the torque converter clutch. Once that starts happening the clutch itself begins to wear out as it starts to slip more and more.

He gave me two options for repair.

First is simply replace the valve body. Its the least expensive (~$1700) and should work fine as long as the clutch isn't too worn out.

Second is a more comprehensive repair and runs about $3500. He drops transmission and replaces valve body but also checks out Torque converter clutch. If its worn out, which he suspects it is given that this issue is two months old, he will replace that as well. I also have a small leak at transfer case where it meets trans (old issue ive been keeping an eye on) that would be fixed by going with this route.

I am leaning toward the second option as I don't want to mess around any more with this. Let me know if ya'll have any input on this!

Dropping Acadia off for repairs on 10/25. Will be sure to update the thread afterward as nothing grinds my gears more than when people don't post what final solution was!

Here's hoping whichever choice is made resolves the issue. (y)
 
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