Hoping I could get some advise. I recently got a sapphire cosworth RWD and it runs fine with no knocks or bangs but at around 65mph+ it seems to be vibrating a lot from the rear. At first j thought it may be the wheel balancing but thats been done and it's still there. I then checked for play on the drive shafts and 1 has slight play around 1mm on the Diff side.
It goes up and down around 1mm inside the diff.
There was also what looks like grease marks over the drive shaft boot where it looks like the boot has been leaking while spinning.

Could this be the cause of the vibration and if not what else can I do to diagnose ?

Thanks is in advance.

 

The U joints in the propshaft can also be a problem

 

Thanks for your reply mate, but I've checked them for play, dont seem to be any there.... however I have since discovered a little play from the centre mount. Wkndering if it could be that

 

The U joints can have 'heavy' points in them. But of course it can something completely different. I would first fix the issue with the drive shaft and see from there.