Transmission shifting hard only after engine has warmed up

JESSICA A RIVAS

MEMBER
2005 CHEVROLET COBALT
4 CYL
4WD
AUTOMATIC
124,546 MILES

Okay, so my car started having some issues. When I turn it on and drive it in cold it works great but when It gets to 180 degrees it starts to accelerate and gives a hit forward. Like when have a rubber band and pull it back and then let it go it hits you. Something like that. This happens only when the car has been driven for a while, but as soon as I turn it off and restart it the problem goes away. I think it must be a electrical problem. I took it about a week ago to a local mechanic and he said it was the motor mounts, (he replaced them and nothing). They also did a transmission oil and pan and gasket change. Then he told me it was the throttle body, also replaced it and no change. Now they told me that maybe it could be the TCM module. Honestly I don't know what to do because I have been to almost every mechanic/ transmission shop near me and no one has told me what's wrong with my car. They only run the code scanner but no codes pop up. Also my speedometer and power steering is working fine so I dont think it's the TCM. Any help would be appreciated

I have been paying attention to the issue and like for example; when I'm at a stop and then I accelerate my car reaches the 2-3 RPMs then give a hard shift and then the RPMs goes back to about 1-2. Then I accelerate again and it goes to 2-3 sometimes 4 the it shifts hard again. * But only when the car is hot.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

They may be correct that this is the TCM or it is another internal issue in the transmission. The only thing that cares about it being hot or not is the fluid and the clutches and seals inside the unit.

If the fluid is new then I suspect you have a clutch/seal issue because what happens when the fluid gets hot is it gets thinner. When it gets hot and thinner, it can cause a small crack in a rubber seal to open up. Once this happens it allows pressure to bleed out of where it is needed and as the RPMs get higher the pressure builds until it bangs into the next gear.

There are times that shifting issues are caused by engine issues but this is less likely.

What I would do is check for codes and go from there.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If there are no codes then I would test the pressure of the transmission when this is happening and I suspect the pressure will be low which indicates there is an internal leak causing the pressure to bleed off.

Let's start with this and go from there. Thanks.