What causes trans to shift hard?

Does it shift at its normal low rpm or does it go higher than usual when it happens? Like tom said also just because the trans is mechanically sound doesn't mean the parts telling it what to do are.

im not too sure about the solenoid, when i called the shop, they said that he had no interest in the solenoid since everything else is sound. as for the rpm of the shifting it goes up to its rpm(say 2500), shifts, then drops down(1200). on a typical 2nd to 3rd shift. at average acceleration....

So the rpms don't go higher when it happens, it shifts at the same point as when it doesn't do this?

could be a blown diaphragm; try changing the vacuum modulator.. that should bring the shift down to 2000 rpms as it should be. if not, there are other slight problems.

Jason its all electronic no vacuum lines involved. The throttle position sensor controls that now.

Finally got someone from Weber Transmission to get it to duplicate the harsh upshifts as they call it, come to find out that the last time they "flushed" the tranny fluid, that the sediments werent completely flushed. thus creating a periodic problem.... fortunately it was caught in time and didnt damage the transmission. they flushed it properly, removed the sediment, and no more sticky shifts.... you shouldve seen the buildup they removed... i got to watch it... also, the key to the guy figuring it out, was that if i stop and move the shifter back and forth and then start it back up it was fine.... i was just clearing the blockage until the next time it cycled through again.... kinda like a moving blood clot.... thanks everyone for your help it was greatly appreciated.....

That's why the pan is supposed to be removed cleaned completely and filter replaced before the "flush" is done. Only reason it would need flushed is to remove the old fluid from the torque converter.

i see.. you need to change your X-mission fluid at GM specified times. i do mine every 40k miles to avoid that.

had my transmission rebuil it was sliping 5 week ago still slip by new millennium ask for my refund back no refund so i am takeing them to court can u help me with my transmission slip

Nothing I can have you do unless you want to swap or rebuild it yourself bud.

Mines hard shifting from 2nd to 3rd and 3rd to 2nd. Just started. I have 198,000 on my 04. I love my car, don't have much cash, and want to remedy it. Any advice. Cars in mint condition otherwise.

I have a 2005 Grand Prix and I was also experiencing the occasional hard shifting. Two weeks ago I switched to high octane fuel and the hard shifting has not occurred. Give it try, it's a lot cheaper than throwing parts & unnecessary repairs at it.

My goodness that's cool I am going to do that to see if this helps my hard shifting....and I will be watching the shifting as it goes into different gears my RPMs seem to stay pretty normal but the shifting is hard sometimes some days are better than others it seems to me I did get motor mounts that did seem to minimize some of the knocking I do have a question though does this car have any dog bones that go on the transmission I have a 2005 GT

Get some MAF sensor cleaner and clean the MAF sensor. The oils and other debris get on the sensor, then the PCM does not get a good reading and doesn't send the signal for more fluid pressure to the tranny.

I have hard shift turning left and going around traffic circles, have grand prix 2006, started couple weeks ago had new converter put in and still doing it shop doesnt know what is causing it going to trans shop in am very frustrating taking back to mechanic several times

I am having hard shifting problems with my 2006. It just started 2 days ago. It had been raining and when I got in to go to work in the morning, I put in my keys and turned the ignition and all the power went out. It did this 6 or 7 times. I could hear what sounded like an electrical arc each time. Finally my car started but now it shifts hard. Any ideas why?

2003 Grand Am with 3.4 v6, twice this has happened and both times it was the MAP sensor, doing original equipment this time instead of aftermarket.