What causes trans to shift hard?

110

Asked by Oct 22, 2012 at 10:30 PM about the 2002 Pontiac Grand Prix SE

Question type: Maintenance & Repair

Every so often, almost once a month, when i am driving i notice that 1st to 2nd is smooth but 2nd to
3rd and 3rd to 4th shift hard, pretty much the car kinda jolts when this happens. if i stop, say at a
stop light, turn the car off, then press the brake and run the shifter through each of the gears, twice,
turn the car on, it stops. what is happening and can i do anything to fix it.


All the transmission shops say that the transmission is in superior shape for having 150k miles on it.
according to their machines.

13 Answers

241,905

So didn't they inspect the transmission shift solenoid?

5 of 5 people found this helpful.
33,985

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.

5 of 5 people found this helpful.
110

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....

4 of 4 people found this helpful.
33,985

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

4 of 4 people found this helpful.
7,185

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.

3 of 3 people found this helpful.
33,985

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

2 of 2 people found this helpful.
110

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.....

7 of 7 people found this helpful.
33,985

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.

1 of 1 people found this helpful.
7,185

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

1 of 1 people found this helpful.
10

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

1 of 1 people found this helpful.
33,985

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

30

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.

3 of 3 people found this helpful.

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.

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