Automatic transmission thump at 60- 70 Kph

[apache]

Would be very interested to know if anyone knows of any problem with the Automatic Transmisssion on the VX. In my case at around 60 - 70 Kmph when going uphill the transmission seems to brake and cause severe thump as if hunting for the right gear. Holden Service reckon this is peculiar to the VX and have noted it on the Extended Warranty. The vehicle now has 27000 K on the clock but the problem has been there from approx 17000 k. At other speeds the transmission appears to change smoothly.
After the six month service the thumps are not so severe, but are still there.

 

[grafxworld]

same problems on VT v6

Our vt does it on hot days going up hill feels like it's going to blow up. loud cluck with a slipping feeling on part throttle at about 80k-100k

 

[apache]

Glad I am not the only one with this problem. Now you mention it, the hot weather does seem to bring on the transmission lock. Maybe the viscosity of the transmission fluid changes. But I cannot see why it should cause the gears to clunk.

 

[grafxworld]

Not sure, mine even has new fluid in tranny, but every time it's over 35 and I go up a decent hill at mid throttle the tranny and or motor feels like it's thumping for a sec then stops for 30 sec or so and does it again until I back off totally to light throttle,,,, it feels like a knock sensor on the motor but the motor has hi octane fuel in it so it should be knocking.
I also notice the A/C is on at the same time it happens ? not sure it thats related.
the feeling is not a good one when it happens, feels like a stick car that jumped out of gear for a split second.
I'm new to commie ownership and GM cars in general but living in america I know that have issues with trannys and motors mostly leaking.
I've got a friend who used retired from chevy as a mech. so I might email him to see what he says.

 

[apache]

Yes you have described the situation very well It feels like a sudden brake has been applied and have to either increase of decrease throttle to get it to continue uphill without stalling completely. I have also noticied that it is more likely to occur when there are a couple of passengers . So we have: hot weather, full load, uphill and aircon as the likely culprits, which indicates some sort of design deficiency. Wonder if GM has any line on this??