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Transmission All about the Chevy Cobalt Transmission

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post #1 of 3 (permalink) Old 08-11-2015, 10:47 AM Thread Starter
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Transmission Roar

Hi, I have a 2007 Chevy Cobalt, 4cyl. with automatic transmission and 72,000 miles. I recently replaced the cv axle. When trying to remove the cv axle the whole axle came out of the transmission. I didn't think there was a problem but I had a mechanic who was working on another vehicle of mine take a look at it. I noticed the keeper wasn't on the axle but he said it was probably still in the transmission and would snap into place when the axle was installed. He completed the work and upon going for a test drive the transmission shifted perfectly although the transmission was making a low roaring sound. I had never had any transmission problems before so it has to be related to the axle being removed. I continued to drive the vehicle since it was my only means of transportation. After a while the car began to act as though it was running out of gas and the speedometer was fluctuating between 80 to 100mph. My actual top speed couldn't have been more than 30mph. I took the vehicle to another mechanic and he said the speed sensor was bad. He also said the gear that the sensor feeds off of had a groove worn into it and recommended replacing the transmission with a used one. He said the price of a used transmission would be less than having this one repaired. After he replaced the speed sensor the car ran fine but he said that was a temporary fix. After several more weeks the sensor went bad again. I removed the sensor and the end had been rubbing against something. I replaced it and the vehicle is running fine but still making a low roar when the transmission is in gear. You can put the car in neutral while going down the road and the roaring stops but as soon as you go back into drive the roar starts again. If the keeper wasn't left inside the transmission and didn't lock in when the axle was replaced, would that cause this problem and if it didn't lock onto the axle, where would the keeper have gone? I know driving the car while it is making this sound is not good but it's my only means of transportation at the time. Driving it can only make matters worse so I need to get it fixed as soon as possible. Any advice would be greatly appreciated. Thanks
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post #2 of 3 (permalink) Old 08-11-2015, 10:59 AM
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I think somebody misdiagnosed from the start. the symptoms you are describing sounds like you have a bad exit bearing where the axle goes in the transmission. Remove the axle and verify that that bearing hasn't fallen apart.

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post #3 of 3 (permalink) Old 08-12-2015, 12:34 PM Thread Starter
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I'll remove the axle and take a look. I'm not sure how the transmission works but a bad bearing on the axle shaft would cause the gear that feeds the speed sensor it's information, which it also on the axle shaft, to be out of alignment causing it to rub the sensor, therefore causing the sensor to fail. Does this sound logical?
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