Hard Shifting

[Jerry 05]

Recently bought an '05 Grand Prix GT with 126,000 miles. It really is a clean car. Had the tranny pan dropped (pretty dirty) and completely cleaned out during flush and also had some other preventive maintenance done. A few weeks later had the throttle control module replaced because when starting the car would just die after the engine turned over. Once that repair was done my mechanic called and said the car started and ran great (he drove it 30 minutes). When driving the car home after the control module was replaced all of a sudden the car began shifting extremely hard with very little power to accelerate. The entire car would jerk when it shifted. Pulled off to a side street and the same continued until I got home. My mechanic (who is a high school classmate and has been in the business 31 years) came over to my house because he was bewildered and actually gives a darn and got in the car, stated it and it ran like a champ. His idea was maybe something had got sucked up into the mass air flow sensor while I was driving home but that is almost impossible he said.... The car then ran perfectly for a month. Then in the last couple weeks, randomly the same hard shifting will happen but not as extreme? My 16 year old son is driving it so he isn't too mechanically inclined but I worry about his safety. I told him when the car acts up, pull off the road, shut it off and restart it. When he does that it runs fine again! Any ideas????

[WarStryker13]

That's the trans going into "limp" mode, it increases line pressure because it senses a slower shift than normal.

$45 bucks for a TransGo shift kit off Amazon, and a bottle of Lucas stop-slip will most likely cure the issue.

[Fivefingerdeathpunch]

When it starts shifting hard, pull the codes before shutting the engine off. Though that is not easy to do, it's the best way to insure that you see the code. It may be possible that is will be a stored code on the transmission side.

Most transmission related codes do not set the check engine light. I tend to agree that it's throwing a P1811 max adpat shift code and causing the harsh shifting. A shift kit can stop the issue from happening.

[rickisrad]

^^I agree with them.

About the Maf sensor, have you Pulled it and made sure it is clean?

[Jerry 05]

Thanks for your reply, so what you are saying is the tranny literally "resets" each time the engine is shut off? That is why turning the engine off and restarting seems to "cure" the issue?

I guess i am confused as to why it happens at completely random times and according to my son it acts up immediately after starting once it is put into drive, not 5 minutes later or when the engine warms up?

Then he will start and drive the car 15 times in a row without a problem and then the next time he starts it and takes off to go somewhere it happens....

Not to sound completely stupid, but how does the shift kit correct the issue?

Thanks again!

[Bronco Boy]

Thanks for your reply, so what you are saying is the tranny literally "resets" each time the engine is shut off? That is why turning the engine off and restarting seems to "cure" the issue?

Yes.

I guess i am confused as to why it happens at completely random times and according to my son it acts up immediately after starting once it is put into drive, not 5 minutes later or when the engine warms up?

Then he will start and drive the car 15 times in a row without a problem and then the next time he starts it and takes off to go somewhere it happens....

That is how it can go down. Mine would do it every time I started the car for a few days, then nothing for a few more days, then back to every time.

Not to sound completely stupid, but how does the shift kit correct the issue?

Code P1811 is from the transmission shifting milliseconds to slow (due to worn or faulty internal parts). The shift kit ensures proper shift times, thus no chance of the code coming back. I've had mine installed for over 5 years now and no P1811. It is a band-aid solution as you aren't really fixing the problem (usually the pressure control solenoids go bad), but it is a good option.

[WarStryker13]

It's a quirk of the 4T65E, I guess you could say. They're iffy at best.

The shift kit physically forces the transmission to shift to the next gear faster, by increasing the pressure required to overcome the new stronger springs in the accumulators. A tune could do the same, but shift kits are cheaper.

There's probably other issues inside the transmission, input clutch piston seal, worn clutch packs, bad solenoid, buildup of clutch material in the valve body, etc... But the shift kit with a bottle of Lucas stop-slip will help prevent most of those from getting worse and can delay the need for a full rebuild for years in some cases.

[Bronco Boy]

Jerry 05, give this a read.....
http://www.grandprixforums.net/threa...Shift-Solution

[WarStryker13]

DISCLAIMER: my transmission is one of those freak unicorns, it won't even go out of neutral if it's cold. It'll slip occasionally until it warms up. I've got the trans-go shift kit in it, along with two and a half bottles of Lucas and the trans file has been tuned... It's actually pretty impressive how many "bandaids" have been thrown at the damn thing.

There's still some hard shifts every once in a while, and it without a doubt needs a full rebuild, but I'm slowly stockpiling parts to build it into a "performance" trans. It'll hold until I have everything, but if I hadn't done anything, it would be undriveable by now.