6t30 transmission problem

[The34]

Hi guys,
I have a 6 speed auto with 1.4 engine ( no turbo, like 1.8 engines in U.S.)
My problem is car jerks when in some gears. I mean 1-2 shift is fine but other gears have problems. For example sometimes when changing 3rd to 4th gear car shakes back and forth two times then engages. Sometimes it shifts smoothly through all gears so no consistency with car’s actions. Most of the time when I feel the car’s gonna shift, I let off the gas and transmission shifts fine.
Similar problem occurs when downshifting from 6th to 5th gear and it’s some kind of consistent. . When car slows down (let’s say approaching to red light and let off the gas pedal) car downshifts 6th to 5th gear with a jerk ( takes 2 seconds to downshift, Car feels response-less during this downshift)
Other downshifts feel like I break too hard causing a forward lurch and returns to normal.
Anyone having similar issues and can offer a fix? I’m open to all recommendations because I’m thinking it could be something other than tranny itself.

 

[JTee2017]

What year ? How many miles on the car?
And. .. has the transmission fluid ever been changed?

The 6T30/40 actually should have the transmission fluid drained and filled every 30,000 miles for long life. It gets very black quickly.

Check out Chevy Cruise tranny fluid change videos on Youtube. Same transmission . . same procedure.

Bascially, drain out when warm, measure the amount drained and refill with fresh Dexron VI fluid. Start the car foot on brake and move the shift lever through all positions. . . . pausing in each for 5 to 10 seconds. Do it several times. Then drive for a day or two.
Repeat the above 2 more times and then check the side level check bolt port after driving a good long time and with the car level, take the bolt ou of the tranny side check port car in park and running . . .. fluid should just drip out a little. . . if it doesn't add a bit at a time till just a drip comes out.

 

[The34]

Thank you for your response, 2012 model with barely has 60 miles on it. Transmission oil is brand new and changed the solenoids as well. According to the transmission shop it’s all good on tranny side, they found nothing wrong internally. Of course I’m gonna go to the shop again, I’m waiting for 1000 miles “relearn procedure” period to be end.
I’m beginning to think something triggering this anormal behavior. Because it’s not consistent, sometimes it shifts smoothly like a dual clutch, and sometimes it shifts like a new driver driving with a stick.

 

[The34]

A bad battery caused my radio to off and on again, locked the doors and unlock them, even powered down the ecu causing engine to shut down. Since newer cars are so complex it made me think some sensors or faulty parts are causing this shifting problem. Of course I’m not saying it’s not the transmission but I’m open to any suggestions

 

[JTee2017]

A bad battery caused my radio to off and on again, locked the doors and unlock them, even powered down the ecu causing engine to shut down. Since newer cars are so complex it made me think some sensors or faulty parts are causing this shifting problem. Of course I’m not saying it’s not the transmission but I’m open to any suggestions

First. . maybe go back to whoever replaced the transmission and have them check all electrical connections and ground points to the transmission and engine block.
Also, the plastic electrical connectors to the transmission could be corroded or damaged and the service people may have missed that.

Or you can try the following yourself - - -
Perhaps carefully check the condition of the battery cables . . . especially the negative cable and follow it to where it connects to the engine block and transmission. As i recall, depending on model year, the negative cable has several grounding points to the body and engine.
Since you had the transmission replaced or worked on, i would make sure any electrical negative ground points are in good condiition. Wiggle and pull on them a bit to see if they are secure. The wire can look good. . . but where it is crimped onto a terminal end like going to the engine, transmission, or engine. . . it can be bad.
You could even temporarily run a separate wire from a transmission bolt to the negative battery terminal and assure a good connection and see it that helps.
Your symptom being erratic, sound electrical in nature possibly.

 

[The34]

Thank you again for your attention. It seems logical, a bad wire Or connection causing electrical issues and affecting transmission. I’ll try to look into ASAP

 

[The34]

You could even temporarily run a separate wire from a transmission bolt to the negative battery terminal and assure a good connection and see it that helps.
Your symptom being erratic, sound electrical in nature possibly.

Just did that. It did not help, still that jerky shifting in some gears( up and down)

 

[JTee2017]

I guess then, I'd take it back to whoever replaced the transmission. They should warranty it and trouble shoot why it is doing that.
Was it a NEW transmission or "Rebuilt"? Rebuilt . . . you never know how good the people were doing it and how well they did the job or replaced ALL necessary worn parts.

 

[Gobinator98]

That jerky shifting is normal in these cars. Nothing you can really do about it. Other people on these forums have had good luck replacing the transmission in their 2012 sonic with one from a 2014 or 2015 and that results in smoother shifting from the updated design. I will be replacing mine with a 2015 transmission.


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[The34]

That jerky shifting is normal in these cars. Nothing you can really do about it. Other people on these forums have had good luck replacing the transmission in their 2012 sonic with one from a 2014 or 2015 and that results in smoother shifting from the updated design. I will be replacing mine with a 2015 transmission.


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I don’t think it’s normal. When it performs it shifts smoothly but when it decides to act weird it shifts harshly into the gear(or out of gear). (Don’t know the exact car terminology)

 

[Gobinator98]

I don’t think it’s normal. When it performs it shifts smoothly but when it decides to act weird it shifts harshly into the gear(or out of gear). (Don’t know the exact car terminology)

That’s normal for the automatics in the 2012 and 2013 model years. There is no way to prevent it unless you put a transmission in from a new model, but even that doesn’t always work. If you read the forums on here, it is a very common occurrence and it is stated many times that the dealer said it was normal and there was nothing wrong.


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[The34]

That’s normal for the automatics in the 2012 and 2013 model years. There is no way to prevent it unless you put a transmission in from a new model, but even that doesn’t always work. If you read the forums on here, it is a very common occurrence and it is stated many times that the dealer said it was normal and there was nothing wrong.

Dude don’t get me wrong, I’m not try to be rude or anything but I’m the one who drives the car and I can tell what’s normal or not. Like I said in previous post
1-2nd shift
generally fine, sometimes (when going downhill with no extra throttle) shifts badly
2-3rd shift
on cold starts it revs much higher than usual and shifts badly as well
3-4th shift
Well this is unusual, feels different from other gear changes, sometimes car wobbles back and forth two times and engages
4-5th shift
Sometimes on a cold start, when it shifts 4th to 5th for the first time, sometimes it shifts badly
5-6th
it’s good

Most of the time 6-5th downshift is bad and other downshifts feel like I’m pressing the break pedal too hard(though I’m not), makes the car lurch forward as well as passengers

 

[Gobinator98]

Dude don’t get me wrong, I’m not try to be rude or anything but I’m the one who drives the car and I can tell what’s normal or not. Like I said in previous post
1-2nd shift
generally fine, sometimes (when going downhill with no extra throttle) shifts badly
2-3rd shift
on cold starts it revs much higher than usual and shifts badly as well
3-4th shift
Well this is unusual, feels different from other gear changes, sometimes car wobbles back and forth two times and engages
4-5th shift
Sometimes on a cold start, when it shifts 4th to 5th for the first time, sometimes it shifts badly
5-6th
it’s good

Most of the time 6-5th downshift is bad and other downshifts feel like I’m pressing the break pedal too hard(though I’m not), makes the car lurch forward as well as passengers

Dude.....not trying to be rude. But I got the exact same year, engine and transmission as yourself. I have the exact same problems and have been told nothing is wrong and everything is normal when I have brought it in. Other people people have been told the same thing when taking it to the dealer.

I gave you a suggestion about switching the transmission with a compatible one from a newer model since other people have had success with achieving better shifting performance. But if you don’t want to take that route, then that is fine. But unfortunately if you have tried shift solenoids + fluid and a few other things, then I don’t know what else to tell you. I’m only responding and trying to help you because I’ve dealt with the same issues the whole time I’ve owned the car and then some. These are very weak transmissions and tend to barely last longer than 100K. Even my 24 year old Corsica (with a 3 speed transmission) I had before the sonic shifted way smoother than any other car that I’ve drove, including the sonic.

Do with this information as you will. Have a nice Memorial Day!


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[The34]

Should’ve gone for a vw group for dsg nevertheless I’ll pay a visit to the transmission shop on Wednesday and see what says. If they managed to fix it I’ll write here

 

[Gobinator98]

Good luck!


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[gnonne]

See if it has the same bad shifts in manual mode.

I've had 3 2012-2013 sonics, all with the 6-sp auto. They rarely shift bad. When it does, it is low on fluid.

 

[The34]

Well i pick up the car from the transmission shop yesterday. They said they changed everything inside with the brand new ones. I’m gonna drive the car and see if it made any difference.
One interesting thing is they said they didn’t calibrated it. I know Fast Learn Adapt Process is required when repair is performed. Should I do something about it or wait for the car to learn itself?

 

[TitanBlue]

Did your Transmission learn anything? What is the outcome?

 

[The34]

Spoke with the owner yesterday, he said new trannys will be in stock next wednesday so we are gonna try them.

****box doesn't learn anything but I learned where the shift points are, when in proper speed, i let off the gas pedal and it shifts smoothly :banana:

 

[TitanBlue]

What is it costing roughly to install a new Trans? Parts and Labor?