Computer creating transmission problems

impala
chevrolet

#1

I have a 2008 Impala, bought used, with 67000 miles on it. Last year, the car started having what I thought was intermittent transmission problems. When I would stop at a light/stop sign, and then accelerate, it would hesitate momentarily and then take off with a thud. It felt like the back wheels were spinning but couldn’t get any traction. I was also having a hard time getting it out of park and into reverse if the rear-end of the car was lower than the front. There are no check engine lights when this happens and it doesn’t happen all the time. I took it to my mechanic first and they couldn’t diagnose it, so I took it to the Chevrolet dealer. The dealer said that this was caused by the computer and that it needed to be reset. They reset the computer, which helped for about 12 hours. I took it back and they said it was operating within normal specifications. Does anyone have any ideas about what is causing this and how to fix it? Thanks.


#2

"It felt like the back wheels were spinning but couldn’t get any traction.

Now that’s really weird, since it’s a front wheel drive car.


#3

There could be several things causing that. A leaky clutch would cause the momentary neutraling. The computer is another. What really needs to be done is to run the vehicle with the scanner attached and see whats happening when the problem occurs. You stated that this is an intermittent problem. Was the dealer able to duplicate the problem??

transman


#4

If the clutch is leaking, would there be spots on the ground under the car indicating a leak? It did its thing once when the dealership had it, but didn’t do it again when they were test driving it. They ran it on a scanner for about 12 hours and didn’t get anything. When it idles, it doesn’t have any problems. When it does it, I definitely feel the thud in the back, right about under the back seat. We took Hwy 35 to Corpus last March and it did it several times when we stopped at the traffic lights and then started again. Thanks.


#5

There would be no sign of leakage–the leak is internal to the transmission and basically means that it takes longer for the pressure to build up before the clutch can actuate.


#6

Forgot to mention that this is an automatic transmission–don’t they use torque converters rather than clutches? Thanks.


#7

They use a torque converter - which is more or less instead of a clutch as the link between the engine and the transmission for a manual trans. But the torque converter isn’t involved in changing gears.

Each gear in an auto trans has a “clutch pack” - basically works the same way as a regular clutch but the engagement and disengagement are controlled by fluid pressure. If you didn’t have clutch packs to give some slip and smooth engagement between gears you’d have whiplash and broken transmission shafts (not to mention no actual motion). The torque converter itself actually has a clutch that, at certain times, will lock the transmission & engine together so that they both spin at the same speed. (Its gives better fuel economy and keeps the transmission cooler).

Anyway, you need not a dealer nor a local mechanic. You need a local shop that specializes in transmissions. The dealer doesn’t want to be bothered, your local mechanic (unless a transmission specialist) probably can’t handle it.

Be prepared for annoyances and perhaps an ongoing saga. The transmissions in those cars are great when they work. But they often don’t work and when things start to go wrong finding remedies seems to be something of a crap shoot. GM can’t even get straight on all of the things that might go wrong and what to do about it when it does. Its likely a 4T65E - search the web for similar reports if you like.


#8

I will repeat what I often advise as one of the inital steps,search for Technical Service Bulletens. Transmission isuues are well covered in TSB’s. Finding a TSB related to your problem could save you a ton of money.

There is one TSB for your car that states a 2-3 upshift and 3-2 downshift “clunk” is normal and no repairs should be attempted.


#9

Yes, I’ve read those and I’m not sure they are talking about the problems my car is having. The slow shift bothers me because if I had to get out of someone’s way at a light, I couldn’t. When the slip happens, it takes 4 to 5 seconds before the car starts to go after I step on the accelerator. And then when it does go, there’s a thunk and a hard jolt. It’s a hard enough jolt that if you were holding a drink in your hand, the liquid sloshes out and it actually moves the people inside the car forward and back like if you have to stop really fast. So it makes me thinking something’s eventually going to break in the transmission and the dealer won’t fix it until it’s out of warranty.


#10

I was going to ask you about warranty as I thought you were in but I saw 68000 miles. Are you still in warranty for some reason?

We have a current post from a person with a Saturn and no second gear, this person is A OK with not being able to get out of someones way.


#11

What you are describing is called “Neutraling” It is a loss of fluid pressure, in your case in the forward clutch assy. It goes back to what I said earlier about a leaky (forward) clutch. Piston seals can cause this, sealing rings or worn bushings will also do it. The pump itself could be leaking internally and not regulating pressure properly at the lower RPM’s. If I were working on this I would now be putting a pressure guage on the trans to check the hydraulic integrity of the forward clutch. I’d let a trans shop have a look. They might test it they might not. Bottom line is you are losing pressure and the only real cure is to take it apart.

transman


#12

Thanks for the info. I will take it to a transmission shop and have them look at it. The strange thing is that it only does it when the temperature is about 75 degrees or lower, so I usually don’t have a problem in the summer. The ironic thing is that I got rid of my 2002 Impala (which I really liked) because it was having transmission problems, only to get another Impala with problems. I’m not buying another Chevrolet after this.


#13

I conclude this means you are not under warranty, when you said "the Dealer won’t fix it till it is out of warranty, I wondered.


#14

This might help you. Rubber clutch piston seals harden with age. When they harden they tend to leak. The cold will cause these already hardened and leaky seals to leak even worse. As the transmission warms up the hardened seals will soften up. When they do, they will hold hydraulic pressure better allowing the clutch to apply faster and hold better. Thats why the transmission is worse when cold.

transman