4T65E 2006 Buick Lucerne Normal decel gear banging

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I bought an original owner 2006 Lucerne last year. Only about 5k miles put on it since I got it, with near 80k miles on it now (3800 motor.) When I got it, I did several drain and fills with Dex VI. Put a little Lubeguard red as well. (I know some of you say a waste/don't do it with Dex VII) The car/trans was running fine, probably original fluid, and the fluid was reasonable looking.

My daughter had the car at college and I just got it back to daily drive again. On decel to stop or near stop, if I get back on the throttle quick or hard, the car will bang into gear. My best guess is that the trans isn't done downshifting cleanly into 1st (?)

I had read and debated the accumulator mod, which I'm ready to do, but wonder if anyone has additional suggestions before I just do that one part of the Transgo kit alone. The car seems to shift pretty near perfect and smooth on any variety of throttle position otherwise.
 
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Originally Posted By: lexus114
this might sound stupid, but try clearing the ecm with a scanner or neg batt cable. see if that helps.


Thanks- that can't hurt. After driving it for about another week, it hasn't happened again. I'm going to leave well enough alone. When my daughter had it this past college year, it was used infrequently. It will get used every day by me now..that may be better for the car overall.
 
I had a 2001 Grand Prix with the same trans. The shift kit definitely helped my car. One other time I started having erratic banging shifts and it turned out to be the MAF sensor. I tried cleaning it but ended up replacing it and never a problem since. I was the only owner of that car from new to 230k miles. Still shifting great (occasionally slightly rough when really hot and in city driving) when I gave it away. Earlier years used Mobil 1 ATF then switched to Dex VI later on. Tried Redline D4 in it once but was no better for the hot weather condition. It was minor so I quit worrying about it.
 
I did get it to happen once more. Car was about 5 minutes into my morning commute through suburban streets to the bus stop, so still a bit cold. Scenario that caused it is familiar to the previous times now - hard braking to a stop sign, full stop, and a prompt take off. So today I was probably doing 40-45... into the hard stop, full stop, and went to make my departure and it hesitated as it presumably grabbed 1st gear. The braking was fairly aggressive and I certainly could avoid it and give up little in driving behavior flexibility.
 
MY 2005 La-Sabre will do the same thing on aggressive hard stop, then accelerate and there is a bang going into 1st gear, then it shifts great thru the next gears. Note, I am also a fan of Lubegard, but it did not stop the 1st gear bang . If I take off normal after a stop, all is well.
Just stop normally when you can , you should be ok.
 
My Century would bang on the up shift, especially during hot weather. Trav hooked me up with the valve body mod about 35K miles ago. It fixed the problem and according to my son it hasn't returned.
 
Originally Posted By: CourierDriver
MY 2005 La-Sabre will do the same thing on aggressive hard stop, then accelerate and there is a bang going into 1st gear, then it shifts great thru the next gears. Note, I am also a fan of Lubegard, but it did not stop the 1st gear bang . If I take off normal after a stop, all is well.
Just stop normally when you can , you should be ok.


Thanks all for the input. I'm now sure the trans is basically fine and the symptom can be avoided simply by not launching nearly instantly after a hard stop.
 
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