What can be done to stop the Citroen C5 Estate shuddering at 70+ MPH?

[Stuart]

Since my Citroen has had gear linkage cable changed, the whole car shudders when speed hit 70 mph..

it just gets worse the more you increase speed.

Anyone Help Please !!!!!!!

[snow]

There is something out of balance start with your tires and wheels and if that does not stop the vibration then look at all moving rotational components, Prop shafts, crankshafts etc. all these components have been balanced at the factory and is commonly known as harmonic balance.