VW t4 vibration at 100kph

[Racemag]

I had new Pirelli Carrier tyres fitted to the T4 syncro as old tyres were badly worn and in poor balance, esp on the front. With new tyres all seemed good until I drove on the fwy at 100kph - there is a significant shake. At 90kph all smooth and 100kph it shakes and it continues to 115kph, which is as fast I ever get this thing to go - the shake increases. I took it back to the tyre place and since the steering wheel was not shaking much they rebalanced the rears - which made it a bit better, but still a shake at 100kph. So I'll go back to the tyre place in the next day or so.
Can it be anything else?
Driveshafts all seem good, tie rod ends are fine. I did check the prop-shaft and I think the rubber coupling to the VC is gone - seems solid and centred - this needs to be replaced and ideas on where to get this are welcome.

[Umai Naa!!]

Might as well get the fronts re-balanced too.

Driveshafts on these well give a big vibration when there's too much axial play in the CVs, but only under load.

[Racemag]

OK, thanks for that. The vibration occurs at speed, not as you might expect there is some load, but not like going up a hill. At any lower speed it is beautifully smooth regardless of load. The issue of high speed mad me check the rear driveshaft and that's when I found the failed GKN coupling. Typically for VW it is supposedly NLA for the T4.
I've spent the evening searching for a replacement flexible coupling for the syncro propshaft and this thread looked like it might have a solution, so I've followed it up: Schwingungstilger Kardanwelle hinten UPDATE ab post 11 - Syncro - T4Forum.de

[Umai Naa!!]

Is it on the front of the prop shaft? Diagram describes the only replacable one to be 'front'.

If so, there are OEM listings from Febi Bilstein and Swag.

Number is 7D0521127

In fact, Tooley Imports in Sydney, have a listing for it.

[Racemag]

testing

[Sunny43.5]

What I find strange with your problem is that the vibration occurred after new tyres were fitted , was there any evidence of vibration up until then ?

[Racemag]

heaps of vibration: previous tyres were shagged and front wheel had thrown a weight.
The coupling is the rear one, which VW say is a non-service item. It's the one before the VC, with the big mass damper. I went on the German T4 forum and the kind gents told me that they use VW 1J0521307C or Febi 19526
Typically the VW Aust price for it is $994 or 604 euro

[Racemag]

I tried to post a link to it on ebay germany where it sells for 160 euro, but this forum did not allow it.

[Sunny43.5]

I put in the part number on Mr Google search and came up with this one is it any good price wise ?Joint, propshaft OE Number 1J0521307C buy online doing conversion with freight came out at $570 AU

[Umai Naa!!]

Find someone who's wrecking a Bora 4Motion, I reckon that'll be the same part.