Has anyone had experience of fitting polyurathane front top wishbone bushes on an X300, particularly an XJR. I already have lowered springs, German spec Bilstein dampers a 20mm diameter rear sway bar and rose jointed front and rear sway bar drop links, so I'm quite happy to compromise ride quality in pursuit of improved handling.

 

I know of a number of XJ40s and X300 with top wishbone poly bushes, consensus between the owners seems to be that out of all front rubber, top wishbone bushes are best(and often only) place for poly as they simply last longer than genuine Jag bushes and offer best handling with negligible drop in ride quality.

 

and the lower shock bushing

 

On my XJR, I have Powerhouse stiffer, lower springs & rose jointed ARB drop links (on standard bar, but with poly mounting bushes). I went for poly lower wishbone bushes, but retained (new) rubber upper wishbone bushes. My logic at the time was that the lower wishbone is carrying more of the load, so I wanted that to be stiffer. As the upper bushes are small, there is less room for deflection, so I was trying to keep a little compliance there. The ride is fine, I too prioritise the handling over the ride quality, but it's not noisy. I did retained the standard (new) rubber subframe mounts. Having experienced the ride now, I'd probably try poly bushes in the upper wishbones too.

 

I replaced all the front bushes on my XJR with polly tying to stop tramlineing to no avail (recent swap to 235/50/17 tyres sorted it at last). I have some transmission of noise / vibration on rippled tarmac, but may just be general wear elsewhere in a 170+K miles / 26 year old car.
The key point I would mention is that unlike bonded rubber, the poly bushes need some sort of bearing surface to take the axial load. The outer face of the 'top hats' on the set I bought where profiled to suit a 'special washer' which I think was from the XJ40 or XJS - sorry it was probably 7-8 years ago. On a lot of cars the polly bush kit offered seem to use the mounting brackets as a bearing face - not ideal in my mind. On our front suspension we need some sort of washer for this purpose - ideally bigger then the hole in the suspension arm to avoid shearing force on the bush flange. A friend managed to source some extra large heavy pattern washers to suit the lower arms.