Short story/question:

would would cause the auto in my 06 g35 to lurch forward violently in gear at idle?


Long story/background:

I built a motor, and got a higher stall tq converter for my auto. Trans already had the transgo valve body upgrade in it. Torqued everything down and started it, fired right up no issues, no leaks. developed a rattle at idle and a couple leaks a couple hundred miles later. the rattle turned out to be the torque converter bolts working themselves loose (and i know i torqued them to the torque listed in the FSM), which i think caused vibrations that led to the leaks. anyway, 1000 miles now on the motor, had a shop tighten the bolts, noise went away. then had them fix the leaks, upper oil pan and rear main seal. also had them do the transmission pan as well since they were under there as it was also leaking. got the leaks fixed, so pick up the car. get less than a mile down the street and am at a stop light in gear at idle engine speed. all of a sudden, the car starts lurching forward repeatedly. i am pushing as hard as i can on the brake so i dont hit the car in front of me. the only way i got it to stop, was to put it in neutral. once you get past a certain rpm, the lurching disappears, probably anything over 1.5k or 2k rpm, so issue is only in the lower rpm. no ses light, shop says everything went back together the way it was supposed to. i never had this lurching problem before they had the car.

any ideas on what this could be?

 

bump

 

no one?

 

Band Brake may need adjusting or the spring broke on servo piston. It seems catastrophic so the servo piston spring likely problem.

 

is a servo piston spring easily replaced?

 

I made a few assumptions but need to be verified.

Are your brakes holding pressure ?
Is the car idling at normal RPM ?
Would have a scan done to check for any codes.
Does the car ever stall when stopped ? If so TC maybe locking up.
Does it shift normally ?


If everything else is normal than continue to pursue Band Brake servo spring. Yes thier easy to replace but need to remove TCM.

Band Brake out of tolerance would cause shifting issues, not sure if thats what your describing below 2K RPM.

Thier are many solenoids that control transmission and need to verify no codes are showing up with scanner before transmission diassembly.

 

Brakes are holding pressure.
idle is normal, very smooth except for a slight roughness from the cams.
i told the shop yesterday to scan for codes and didnt hear back so assume nothing is showing up code-wise.
i didnt drive it long enough to see if it stalled when stopped, but the short time i drove it, it did not stall when stopping. i think one time i may have come close though, but that might have been because it needs a tune too.
for the short time i drove it, the actual shifts seemed fine.

they have just replaced the transmission pan gasket and rear main seal before this started happening, so is there anything that comes to mind on removing and replacing the pan gasket and transmission that maybe they hit or messed up in the process that would cause this?

i will call and see if any codes showed up

 

Don't see any issues with transmission removal/reinstallation that could cause problems your experiencing. If thier are no codes showing up and TC not locking up than servo would be most likely problem.

Haven't seen any threads about High stall TC lock up issues or servo failures on G/Z's.

GTM sells upgraded servo components they use in thier built transmissions.

 

how does one tell if the tq converter is locking up?
thanks for the help btw.