Hi all,

I have a 2004 Vectra C with V6 petrol engine & automatic transmission. I'm from Australia & here the model is referred to as ZC & the brand name is Holden.

When vehicle is cold, there is a harsh 'thud" when downshifting from 2nd gear to 1st gear.
Occurs only for first 3 or 4 kilometres of driving.
Downshifting 3rd to 2nd, 4th to 3rd, & 5th to 4th are all smooth.
When vehicle is warm, the 2nd to 1st downshift is smooth.

All upshifting is smooth.

My local Holden dealer suggested to changeover the transmission fluid. I did, but no change.

Can anybody give me any ideas as to what is might be ?
Worried that I might need to replace the transmission.
The problem started when car had about 90,000km. Now it has 125,000km and problem seems to be getting worse - but very slowly.