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Discussion Starter · #1 ·
Sorry in advance for the long post.

So I think I may have a problem with my trans. On monday my wife was on her way to work when she called and told me that she was hearing an unusual sound coming from the car when accelerating. Knowing that she can be a little paranoid about the car since it is the only one we have and I use it for pizza delivery I figured it was nothing. So later when I am heading to work I notice the sound too. It is kinda hard to describe but the best I can manage it sort of a grinding whine. Now I am starting to get paranoid so i start paying closer attention to the tach. That is when I noticed that if I am cruising along at a steady speed and give it a little gas to accelerate the tach will jump about 500 rpm then slowly settle back to anywhere from where it was at prior to gassing it or as much as 200 rpm lower. The car would continue to accelerate the entire time, even as the rpms were dropping. you could even hear the engine rev up then slowly rev down.

So I take it to my dealership since the drivetrain is still under warranty. I tell them what is going on and they said they would look into it. I even took the tech on the test drive so I could point out exactly what I was concerned about. First the tech tried to tell me the sound I was hearing was my exhaust, which I know It wasn't. Then when I pointed out what was happening with the tach and the engine revving. He tried to tell me that it was just the car shifting. I def know better. I spend about 7 hours a day in my car and I can feel exactly when it shifts. None the less they insist that it is normal.

What I would like to know is if anyone else has experienced this and if so what if any cause was found? There is another chevy dealer nearby that I am going to be taking it too on tuesday and it would be nice if i could go in and possibly point them in the right direction.
 

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just make sure you insist that there is a problem, if you have to talk to a manager and get him to talk to you. if they have another cobalt there then ask them to go with you for a drive in both cobalts so that they can hear the difference. good luck and keep us posted
 

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Discussion Starter · #3 ·
Still no luck. Everyone claims that it is normal. Am now looking for a good local trans shop to have look at it. When update when I hear what they have to say.
 

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re

check your brakes... my 05 balt auto is making the same sound but I've narrowed it down to my brakes (140k on original front pads/rotors)

last time I heard a sound like that it was my a/c belt

I deliver food out of mine too... 70k/yr

I have a prob where if I park with the wheel tight to the left and back up in the same direction then move to drive I will about 80% of the time have a 3 second delay shifting..

but my 4t45e sees 7k several times a day so with that said It's obviously a solid unit!
 

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ok.. now im not totally sure of this but.... i am almost positive that if the trans was slipping the OBD2 would throw a check engine light code... ive seen it in the blazers with the 4L80E trans and i am almost positive the cobalt has a similar system... keep yer eyes out for a check engine lights
 

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Discussion Starter · #6 ·
Found out what the sound was. It turns out there was a tiny leak in the flex piping that connects the front pipe to the manifold. Fortunately I was able to get the dealership to cover it under the emissions warranty. As for the the jump and drop on the tach it is still doing it. hasn't gotten any worse and no codes have been thrown, so I am not going to worry about it right now since I still have about 40,000 left on the drivetrain warranty.
 

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If you deliver food, how fast will that 40k miles come up? Im pretty sure if you keep taking it in for the issue you will have a service log of the problem. This way it will be easier to make them cover it under warranty even if you are slightly over the warranty.

When I was younger delivering wings/subs etc.......40k miles was about 9-10 months.
 

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Discussion Starter · #8 ·
40k will take me a little over a year to hit. I am definitely paying attention for any worsening of the situation and at the first sign it is getting worse i will be taking it back in.
 
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