Thud/Clunk/Jerk When Changing to Drive or Reverse - Pontiac G6 Forum
 
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post #1 of 14 (permalink) Old 08-12-2013, 12:48 PM Thread Starter
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Thud/Clunk/Jerk When Changing to Drive or Reverse

2007 GT 3.5 auto with almost 120k on the odometer.

My wife informs me that recently in the morning she will notice a jerk in the engine when she puts it in drive or reverse. It doesn't really make a noise. Its more like you can feel the whole car shudder for an instant. It just happens once into the forward/reverse gears. It doesn't do it going into neutral or park.

I had her cycle the gears a few times while I watched. It is definitely kicking forward/backwards on each switch. Looks like maybe a motor/transmission mount isn't doing its job.

But it shifts smooth while driving. Even under a heavy load or a spirited take-off. I've checked the 2 mounts I can see, but how and where do I check the transmission mount?

I've also noticed the engine idles very poorly. It bounces almost 700 RPMs randomly when just sitting in park idling. This started really close to when the transmission started jerking, apparently.

Of course both of these problems are more pronounced when the car is cold. Almost none-existant once its fully warmed and been driven for awhile.

So far I've checked the fluid level. It was filled to the top but looks and smells like it should be changed.

The front mount and side mount on the engine are tight. I can't move them more than a few MM with a prybar. Is there a better method to test them?

May not be related but these are the things I've replaced in the past 6 months: radiator, front cat, all O2 sensors, tires, spark plugs, brake pads and rotors all around, and oil many, many times.

No trouble codes at all.

I would appreciate any advice you could give to help me out here. Thanks.

Last edited by s10blazed; 08-12-2013 at 12:52 PM.
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post #2 of 14 (permalink) Old 08-12-2013, 01:34 PM
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When you say the fluid was filled to the top, how did you check it?

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post #3 of 14 (permalink) Old 08-12-2013, 10:30 PM
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To check motor mounts:apply the parking brake and put your foot on the brake and shift into drive and give it some gas gradually, you can watch the motor with the hood up, anything more than 1/4 to 1/2" of movement backwards could mean trouble with front motor mount, do the same in reverse and check movement. sometimes the car can produce more force and show you what is wrong. also look at passenger side engine strut, the piston will show how far the motor moves.
For the rough idle, look at your belt tensoner, does it bounce around or stay steady? if it bounces may need replacing. Mine ran rough, no codes until I changed it.
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post #4 of 14 (permalink) Old 08-13-2013, 05:40 AM Thread Starter
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Quote:
Originally Posted by theshibbykumquat View Post
When you say the fluid was filled to the top, how did you check it?
Well after I replaced the radiator some fluid spilled out so I researched it. I pulled the car onto my ramps and jacked the rear so it was level. I pulled the bolt on the side and filled from the top until it came out just a little. The transmission was warm. The car was not running, though. Some articles I read said to leave it running. Others said to just make sure it was warmed up and recently gone through the gears. I did have to add back in approximately the same amount I cleaned off my driveway.
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post #5 of 14 (permalink) Old 08-13-2013, 05:42 AM Thread Starter
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Quote:
Originally Posted by haliburton G6 View Post
To check motor mounts:apply the parking brake and put your foot on the brake and shift into drive and give it some gas gradually, you can watch the motor with the hood up, anything more than 1/4 to 1/2" of movement backwards could mean trouble with front motor mount, do the same in reverse and check movement. sometimes the car can produce more force and show you what is wrong. also look at passenger side engine strut, the piston will show how far the motor moves.
For the rough idle, look at your belt tensoner, does it bounce around or stay steady? if it bounces may need replacing. Mine ran rough, no codes until I changed it.
Thank you. I will check all of this tonight.
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post #6 of 14 (permalink) Old 08-13-2013, 08:44 AM
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Quote:
Originally Posted by s10blazed View Post
Well after I replaced the radiator some fluid spilled out so I researched it. I pulled the car onto my ramps and jacked the rear so it was level. I pulled the bolt on the side and filled from the top until it came out just a little. The transmission was warm. The car was not running, though. Some articles I read said to leave it running. Others said to just make sure it was warmed up and recently gone through the gears. I did have to add back in approximately the same amount I cleaned off my driveway.
Okay I though you may have filled to the top of the fill cap and that wouldn't be right... But also the transmission needs to be running to check the level properly, not just warm. So I would suggest rechecking the level with the engine running. Also cycle the transmission through all gears once its running and then put it back into park when you check. You want to make sure that all parts of the transmission have fluid in them

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post #7 of 14 (permalink) Old 08-13-2013, 09:19 AM
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Quote:
Originally Posted by s10blazed View Post
Well after I replaced the radiator some fluid spilled out so I researched it. I pulled the car onto my ramps and jacked the rear so it was level. I pulled the bolt on the side and filled from the top until it came out just a little. The transmission was warm. The car was not running, though. Some articles I read said to leave it running. Others said to just make sure it was warmed up and recently gone through the gears. I did have to add back in approximately the same amount I cleaned off my driveway.
It has to be running, if not you are 2-3 quarts low.

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post #8 of 14 (permalink) Old 08-14-2013, 05:40 AM Thread Starter
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Well I guess I better check it again tonight.

Really makes me miss the dipstick on my Blazer.
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post #9 of 14 (permalink) Old 08-14-2013, 10:23 AM
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A little inconvenient. Have ever checked a dip stick tranny cold engine off, level is 1 1/2 to 2 inches over filled, needs to be running and warm.
Needs to be warm because there is a thermo valve to trap fluid in the upper chamber.
My son-in-law ruined a transmission by doing it that way. Never asked, used book.

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Last edited by slls; 08-14-2013 at 10:27 AM.
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post #10 of 14 (permalink) Old 08-16-2013, 06:21 PM
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I had similar issue related to a "Cam Actuator Magnet". I would get a P code and the Traction Control light would come on indicating a "problem".
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post #11 of 14 (permalink) Old 08-20-2019, 10:46 AM
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Assuming the problem has been solved after all these years, what was the issue causing it to happen?? My 2007 Pontiac g6 is doing the same exact thing, only with the no traction control symbol lighting up along with the check engine light. Thanks
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post #12 of 14 (permalink) Old 08-20-2019, 04:09 PM
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I had a similar problem.
As soon as the service traction control light goes out the problem seems to disappear.
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post #13 of 14 (permalink) Old 08-21-2019, 07:20 AM Thread Starter
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Wow, really testing my memory on this one. I got rid of the G6 in 2016 and this issue was 3 years before that. But here is what I remember.

I did re-check the transmission fluid and it was low. Not 2 quarts low, but low enough to feel like I filled it incorrectly. I don't think it was that easy. I recall a motor mount or something, too. It was easy as far as motor mounts go. Shortly after that she stopped complaining about the rough shifting so I am going to say it was 1 of those things.

But more troubling was the BCM. It would do all sorts of random weird stuff. It was even part of a recall if you search it out. It would mess with the brake lights, cruise control, traction control. It would throw lights randomly while driving then go back to normal just as quickly. She got good at opening the panel, wiggling the harness, and putting it back in seconds. Cleaning and re-greasing was the official fix, BTW. We had done that regularly for a few months. It was really the reason we got rid of it. Even a replacement BCM was bound to go crazy again.

It was also leaking oil somewhere around the headgasket or other major seal. I couldn't see where it was coming from but it was doing its own oil changes each month. That is fixable, but the electrical problems were not. So I turned it into a Subaru Impreza and have been much happier since.
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post #14 of 14 (permalink) Old 08-22-2019, 05:52 AM
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Thanks so much for replying back. Glad to see you are much happier with your new ride. If I can’t get to the bottom of it, I might be joining you as well. Thanks
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