It's been years since I've posted here but this place seems more active then any Grand Prix forums and the Bonneville guys were always more knowledgeable anyways sooooo...(and just so you know I had an 89 Bonneville SSE and 96 Bonneville SSEi before I switched to Grand Prixs, and I only did because I couldn't find any decent Bonnevilles around here anymore )

I currently have a '05 Grand Prix GTP with 205,000 km with pretty much zero problems till recently. Every so often (few times a week?) when I accelerate from a dead stop, there will be a thud that feels like car just changed gears really badly. Everything else about the trans is great. 1-2, 2-3, 3-4 and OD all operate smooth as butter. Goes into drive and reverse with zero issue. Shift at WOT absolutely perfect. Just for fun I dropped the pan this weekend. Nothing unusual, no metal chunks, a bit of clutch material on the magnet. The fluid was dark but didn't smell burnt at all. I changed the fluid and filter, threw in a transgo shift kit and put it back together. It now shifts even more perfect, downshift response is fantastic, but still....every so often from a dead stop I get this clunky thud that feels like a bad gear change. Do I have anything left to try other than replace/rebuild the transmission? The car is otherwise perfect and it would be sad if this was the beginning of the end.

Thanks for any help

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2005 Pontiac Grand Prix GTP Competition Group - 43, 000km - L32 3800 - 3.29 Final Gear Ratio - RETIRED
1996 Pontiac Bonneville SSEi - 203, 000km- L67 3800 - 2.93 Final Gear Ratio - RETIRED
1989 Pontiac Bonneville SSE - 222, 000KM - LN3 3800 - 2.97 Final Gear Ratio - RETIRED

I wonder if there is something in the TQ converter letting lose... idk if you have access to a TECHII or something to scan the trans, sometimes shift solenoids go bad. does it rev or slip before it bangs into gear and move?

S

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Shane "RedZMonte"
2004 Z16 Z06: Virgin
2000 SSEi: Kenwood DDX512, 3.25" MPS, ZZP DP, PLog, Puck Mount, NGK TR7's, DHP Tuned
1995 Monte Z34: T04e "60" turbo, 42.5# injectors, Borla Catback, OBDII swap, DHP Tuned, Much more...

This is called delayed engagement, and there isn't much you can do about it with the transmission in the car. My car has had this issue come and go for years. In my case it seems to be depend on the ambient temps. Anyways, you can read about it here under common problem #2:

http://www.gmls4.com/index.php?topic=2773.0

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

Thanks for the replies! It doesn't rev or slip before it goes into gear, just a big thud and off she goes. I have pulled the max adapt/long shift code before which is one of the reasons I installed the shift kit.

The delayed engagement described in that link sounds exactly like what I'm experiencing. I don't think I'm going to tear into the transmission at this point, but it sounds like you can drive a long time like this without issue. I'd say for me it almost always happens when the car has been heatsoaked sitting in traffic on a hot day.

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2005 Pontiac Grand Prix GTP Competition Group - 43, 000km - L32 3800 - 3.29 Final Gear Ratio - RETIRED
1996 Pontiac Bonneville SSEi - 203, 000km- L67 3800 - 2.93 Final Gear Ratio - RETIRED
1989 Pontiac Bonneville SSE - 222, 000KM - LN3 3800 - 2.97 Final Gear Ratio - RETIRED

Install a trans cooler!

_________________
-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles