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Just got our 2012 back yesterday seems it is caused from the purge valve and the mixing canister being bad and leaking which was causing all the hesitation and it sends the computer into a frenzy and creates a nightmare long story but $1200.00 later it finally is fixed
 

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First, I am not a mechanic. My car is a 2012 (purchased in late 2012) with about 107K miles. In great condition cosmetically but with some "old age issues'. I noticed the shuddering, jerking, skipping, quick hesitation at about 106k, about 1-2 months ago. It happens going up small inclines, on flat roads, highways... at any speed and Usually once in the AM and maybe PM. In late December, I needed to change the SPark Plugs and the Water pump ( I had an ongoing leak for about 2 months). My next fix, part of the "annual physical on my car" would be a transmission flush just due to the miles. My aim is to be preventative and plan out potential cost. But I called a mechanic today to find out about the "shuddering" and his 1st thought was transmission. We schedule an appt for Friday with a stop at transmission person. On my way home tonight, the shuddering/hesitation feeling happened many times. My car felt a bit sluggish also. I have no warning light. On some occasions (2-3 times a month), there is a burning smell which I have smelled for years and the dealer could not ID the problem. If it happens to be a transmission issue, would a transmission flush fix the problem. New transmission is definitely not part of my plan. Thoughts?
Hi.
I'm Ken. This is my first post and reply.

I have a 2011 Acadia Denali AWD. I was experiencing a very similar issue, if not the same. The torque converter was the culprit. I purchased a remanufactured torque co=onverter, and, because I am a technician, pulled out the transmission and replaced the converter. it took about five hours, but the torque converter solved the issue.
I purchased a reman unit on eBay for about $170.00.

My symptoms were as follows:
Initially was feeling the "rough road chugged." I thought it was a rough road surface. After shifting lanes I found that it was something with the car.
Light throttle, light load, mostly higher gear ranges. Feeling would go away on deceleration or acceleration and come back once it settled back into light throttle light load cruise. Also noted rapid small fluctuations in the RPMs
I first suspected a misfire, however, if it had a misfire that could be felt for a sustained period, the CEL would hace set and I would have gotten a misfire code. There was NO Check engine light.
My wife, the main driver, didn't feel it around town and on her short highway runs.

A few weeks later and on a long trip pulling a pop up trailer I began to suspect the transmission. I quickly decided the torque converter was not staying in lock-up or that lock up was chattering, creating the "chugged."
I had recently purchased a newer scanner due to rebuilding a wrecked Cobalt SS, needing the air bag function. I was lucky in that I could watch the input and output speed of the transmission. I took it on the long trip and experimented. during the chuggle I saw the slip speed was erratic. based on a later internet search, this led me to the torque converter.

NOTE: The lock-up function of the torque converter clutch used to be an on-off thing. light load, high gear, lock up solenoid would allow the fluid to lock the torque converter clutch. deceleration, acceleration or a brake pedal application would disable the torque converter clutch.
Not so these days.
The way it works now is through a variable phasing of controlled voltage. It is very hard to determine the on off of the converter clutch now. This threw me for a loop since I couldn't FEEL the converter lock up or disengage. The converter definitely fixed the issue.

Not sure if your issue is the same, but it sounds like a torque converter to me. It took me about 6 hours to drop the tranny out, replace the converter, and put it back together. Not too bad of a job, if you've ever done a FWD GM transmission R&R.

Ken
 

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Lubegard 19610 Dr. Tranny Instant Shudder Fixx, 2 oz.
recommended by a trusted mechanic. Eliminated shudder on my 2012 SLT in about 500 miles but had noticeable improvement right away. It's about $8 at Amazon
I have 2009 sometimes vibrate my mecanic say I need torque converter do you thing lubegard will help ?
 

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Hi.
I'm Ken. This is my first post and reply.

I have a 2011 Acadia Denali AWD. I was experiencing a very similar issue, if not the same. The torque converter was the culprit. I purchased a remanufactured torque co=onverter, and, because I am a technician, pulled out the transmission and replaced the converter. it took about five hours, but the torque converter solved the issue.
I purchased a reman unit on eBay for about $170.00.

My symptoms were as follows:
Initially was feeling the "rough road chugged." I thought it was a rough road surface. After shifting lanes I found that it was something with the car.
Light throttle, light load, mostly higher gear ranges. Feeling would go away on deceleration or acceleration and come back once it settled back into light throttle light load cruise. Also noted rapid small fluctuations in the RPMs
I first suspected a misfire, however, if it had a misfire that could be felt for a sustained period, the CEL would hace set and I would have gotten a misfire code. There was NO Check engine light.
My wife, the main driver, didn't feel it around town and on her short highway runs.

A few weeks later and on a long trip pulling a pop up trailer I began to suspect the transmission. I quickly decided the torque converter was not staying in lock-up or that lock up was chattering, creating the "chugged."
I had recently purchased a newer scanner due to rebuilding a wrecked Cobalt SS, needing the air bag function. I was lucky in that I could watch the input and output speed of the transmission. I took it on the long trip and experimented. during the chuggle I saw the slip speed was erratic. based on a later internet search, this led me to the torque converter.

NOTE: The lock-up function of the torque converter clutch used to be an on-off thing. light load, high gear, lock up solenoid would allow the fluid to lock the torque converter clutch. deceleration, acceleration or a brake pedal application would disable the torque converter clutch.
Not so these days.
The way it works now is through a variable phasing of controlled voltage. It is very hard to determine the on off of the converter clutch now. This threw me for a loop since I couldn't FEEL the converter lock up or disengage. The converter definitely fixed the issue.

Not sure if your issue is the same, but it sounds like a torque converter to me. It took me about 6 hours to drop the tranny out, replace the converter, and put it back together. Not too bad of a job, if you've ever done a FWD GM transmission R&R.

Ken
Do you need take off the engine? For change the converter?
 

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My 2011 does something very similar, but at a lower speed. 140k miles on it. Waiting to take it to a transmission guy.

No lights on the dash, no codes on the computer. The only thing it does is take a little over a second to shift from 3rd to 4th gear.
Mine does exact same thing. They told me its the tork converter and I need to replace transmission. I purchased the vehicle 4000 miles ago. Over 4000 to replace.
 
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