Vibration when changing gear (auto)

[RattyB]

Hi all,

I have a Mk2 R75 V8 automatic which has covered 39K. I'm getting a vibration from the back of the car when it drops from 3rd into fourth at between 50 and 70 mph when briskly accelerating.

It's an odd one as all the auto gear changes are smooth and it won't do it urban speeds.

Any ideas I can go armed with the garage would be helpful.

Thanks