Hi last week while driving i felt a major vibration coming from the rear of the car when i was driving above 40kmh, i replaced my diff 3 months ago so my brother thinks its the tailshaft that isn't balanced, does it matter which end of the tailshaft i rotate or does it have to be the diff end?

 

May want to check the simple stuff too since it started 3 months after the diff:
out of balance wheel
warped brake rotor

 

is it just above that speed, or is it under load as well?

 

I get a bit (not major) of vibration in the colder months, but mine goes away after I drive it for a bit. I am pretty sure mine is just the cold fluid in mine......

 

yeh it seems to happen just above a certain speed, dont feel a thing if its under 40 usually, ill try the wheel balancing and the brake rotor

 

If after wheel balancing and brake rotor check and it still vibrates....try reading this thread and doing the CV bucket swap....worked for me... https://www.s2ki.com/forums/index.php?showtopic=693173
also here: https://www.s2ki.com/forums/index.php?showtopic=241367