Converting to sport shocks

I have a 1990 4.0 Sovereign which my wife and daughter complain is too soft and makes them feel sick. I used to have an X300 3.2 sport which was a much firmer ride due mostly, I think, to having firmer green Bilstein shocks.

Is it possible to fit the same Bilsteins to the Sovereign and will this be sufficient to firm it up a bit? Should I expect any complications in doing such a conversion?

Thanks in advance. This is an extremely useful site and this is the first time I’ve needed to ask a question of my own.

Short answer, no. Rear suspension on the X300 is vastly different to a 1990 XJ40.

Any Jaguar saloon that is designated ’ Sport ’ will have firmer suspension than a regular saloon, but, saying that I’ve never heard of anyone complaining or even mentioning that the suspension fitted to a standard car is too soft IF it is good condition. Have you checked the suspension on your car ? It could just be the original standard shocks are very worn. The suspension on an XJ40 works very hard most of the time and lots of parts such as bushes can wear out quite quickly, the same applies to the shocks. Have you tried bouncing the car by pressing down on one corner to check the damping effect of the shocks, there should be no bounce at all if the they are in good condition and working correctly.

Bushes etc. all in good order. Shocks do need replacing hence the motivation for the change and I’m sure that is contributing to the softness but I’m wary of putting on new standard shocks only for it to still make everyone feel sick.

I thought the X300 sport shocks were the same as fitted to the XJ40 XJR and therefore interchangeable between the two different models despite the slightly different rear suspension set up? Is this incorrect?

Thanks guys.

I can tell you with certainty that rear shocks from a 93 XJR will fit a 94 XJ40 Sovereign. I did a close comparison with an old one from my XJR and one I’d kept from my 94 Sovereign. The Bilsteins were almost treble the price of the Boges, but the bright yellow paint apart they are identical to look at. After comparing the resistance using several levers I was left feeling I’d paid an awful lot for that yellow paint. I’m convinced the difference in ride between the two cars is mostly due to the much thicker anti roll bar and road springs on the XJR rather than the expensive shocks, and if I’d opted for the Boges I would not have noticed any difference, but that’s just my opinion. I also thought my Sovereign was a much nicer ride compared to my XJR, again just my opinion.
What I can’t say with certainty is whether my 94 Sovereign was fitted with the ‘soon to come’ X300 rear suspension modifications that Jaguar began using sometime that same year, it was a February built car and I’m not sure when the change began.

94’s and X300 springs don’t sit on a collar on the shock like the 1990 models - way different setup.

Too hard, too soft, too fast, too slow, too cold, too hot, how far, too far, buy them a truck.

Thanks Casso, that’s interesting. I was wondering if there were other differences contributing to the stiffness of the ride.

It sounds like X300 shocks won’t fit but I only mentioned them because I have experience of them. Looking at Sng parts lists it would seem there are black and green (sport) shocks listed for the 1990 XJ40. Presumably these are interchangeable between cars for the same period? Anyone have experience of fitting the greens to a Sovereign?