Bad vibration at exactly 60mph

Hi there I had a vibration in my 89 xjs v12 at 60 mph. I assumed it was the wheels needing balancing. So I purchased 4 new tyres as I was told mine were perished( they’ve been on the car since 96!!)
However now the vibration is worse and strangely it is at exactly 60 mph not coming through the steering wheel, seems to be coming from the rear…
I will bring the car back to check the tyre balancing again. But was wondering if anyone had any ideas if it’s not the tyres…
Regards Scott

Many would suggest checking the transmission mount first.

Could it be driveshaft out of balance?

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Ya there’s a new gearbox mount… Could be the driveshaft… Fingers crossed it’s the tyres!!

Universal joint in driveshaft or axle

What trans mount bushing did you use? Foam, rubber, or poly?And was it installed so the trans can freely ‘bounce’?

It was rubber… Bought from jaguar…think its a rotational issue

I hope your bearings are ok.

From my experience, driveshaft vibration is approximately at 40 - 60 and 120 Km/h.
Wheel imbalance is at 90 Km/h and usually felt only in the front. They must be really bad to feel them at the rear.
Driveshaft imbalance has a much higher pitch than wheels imbalance.
I would look at the transmission mount as suggested and also the driveshaft central bearing.

Thanks will keep you posted