XJRS Suspension - advice needed

[HerefordMark]

I've decided to have a go at the suspension on my XJRS (as I appear to be keeping it - see other posts..!). It's a bit rolly around corners so I assume it needs work. It still sits well, no sagging etc, so I assume springs are OK, shocks probably gone. Am I right? If so, what shocks to use? I am looking at Spax fixed rate shocks - 25-30% uprated over standard, reasonably priced. Original Bilsteins are horrendous, Spax adjustables likewise (fronts OK, but rears at £80 each...). Does anyone know how the original XJRS shocks compared to the standard car? If they were uprated by anything up to 30%, them the fixed rate shocks would seem ok. Anyone got any experience of spring and shock combinations on XJRS? I'm told Konis plus Aston DB7 springs are the ultimate, but at what cost? Can't afford remortgage or divorce!

Any advice, XJRS owners? Glenn, what do you think?

[GlennH]

Hi Mark,
I am delighted you decided to keep the beastie, I take it you tried the fast A road run and convinced yourself of a) the need to keep it and b) the need for new dampers...

I can't offer any specific experience of changing the springs and dampers on the XJR-S as I haven't yet had to touch them. However I can share some information and general thoughts.

As you know, Jaguarsport modified the suspension on the XJR-S, front springs were specially made (shorter and more stiff at 96.5N/mm as opposed to the standard 74N/mm), rear springs were Jaguar sportspack units (41N/mm where standard springs were 30N/mm). The dampers at the front and rear were bespoke units designed and built by Bilstein. I have been unable to find any specific figures for these units, however road test reports at the time suggested the fronts were rated somewhere between standard and sportspack dampers. My feeling is the rears would be of a similar specification.

With regards to manufacturer, I have tried Spax, Koni, Monroe and Bilstein over the years (but not on Jaguars) and always preferred the Bilsteins - expensive but best ride and longest life in my experience. However at about £135 per damper I can see why you don't want to go that route. Over £800 on dampers is scary.

However, the first thing to ask is if you really need to replace them; dampers don't have much effect on body roll, so unless you are getting a 'bouncy' ride, you may not need to do anything. Have you tried the age old test of giving each corner of the car a good hard shove downwards? You should feel a significant resistance on the way down and once released the car should rise just a fraction above normal height and drop back just once - no bouncing. Not very scientific, but will highlight totally knackered dampers. More easily detected at the front than the rear due to the dampers being paired at the back.

On the general subject of body roll, my XJR-S does feel like it rolls more than my mate's 3.6 sportpack XJ-S, but the lack of rear anti-roll bar and the odd mix of tyre profiles probably account for it.

Hope this has been helpful. It would be well worth contacting David Marks for his thoughts on replacements too.

Regards,
Glenn.

[HerefordMark]

Thanks Glenn. I didn't need to even drive it - just started it up (which I hadn't done for over a month) and listened to it!

I am pretty sure the dampers at the rear are shot. It's not that the car rolls so much, but that it is inconsistent, it lurches. It doesn't feel as solid on the road as my old diesel Merc, which is no sportscar but is currently better to drive. I had a similar thing on my Jensen - changing springs and fitting Spax adjustables transformed it. I don't really want to change the springs because as you rightly say, they are not the same size as normal ones. My thesis is that the springs might have gone a bit soft, but as long as the car isn't down on its knees (as the Jensen was) then they still have life in them. Apparently Colin Chapman used to swear by a combination of soft springs and gard dampers, so that's what I will try.

Thanks also for the info on the dampers. I wasn't sure about the rating of the originals, but if they were softer than sportspack, which are apparently about 30% stiffer than normal, then the fixed Spax might be OK. POint taken on choice of damper, price is the killer I'm afraid. Personally I don't mind a hard ride (ooer, missus...) although I know some would say that a Jaguar should not have a harsh ride.

So, I'll give it a go and report back on the results.

HM

[chris211083]

HI, how did the spax go??? my xjrs has adjustable spax and they are knackered. im gonna go for what my 5.3 xjrs had which was bilsteins front, standard rears. nice combo. let me know how you went on?