i have a vibration that apears at 45 and shakes the whole car any help please

possible propshaft bearing gone, also chack all wheels for play and check wheel nuts

 

some older cars with uprated alloys (bigger), suffer from old nuts coming loose due to stretched threads on them

 

but i reckon deffo propshaft bearing

not being cheeky but looking at your user name, it is a 300zx you are asking about and not an almera aint it

may possibly need the wheels realigning or tracking perhaps!?