Does anyone have the Simply Performance suspension kit with Gaz shocks and Eibach springs installed? Would like to get real world impressions of the setup. Looking to make my '87 V12 feel more like a sports car and less of a cruiser without being harsh.
Hmmm, I didnt know Eibach made performance springs for XJS? I was going to get the 1" lowering performance springs from SNG. Please link to Eibach, I’ve used them on other cars and am very happy with them.
I put Bilstein yellow shocks on my XJS, helps a lot, but you definitely feel the bumps in the road a bit. Not terribly harsh.
Biggest improvement i can tell that i still need is a rear sway bar! I still don’t trust the rear end over 60mph on turns.
It’s on this page. I think they only come with the kit.
https://simplyperformance.com/performance-parts/
Because of the Ford crossover in the early 1990s, the Aston Martin DB7 has the same suspension as the XJS. I have stiffer, and lowered, DB7 springs in my XJR-S and the adjustable Gaz shocks. You don’t need to turn them up very much for it to get quite bumpy.
When TWR did the performance suspension mods for the XJR-S they stiffened the springs and shocks, and removed the rear anti-roll bar. Also, the set up angles are slightly different from stock. I’ve not noticed any problem with the rear end of my XJR-S in high speed corners.
Ride height can be adjusted several ways; shorter springs is one of these, but the others involve the use of spacers between the lower spring pan and A arm on the front, and either spacers or the use of shocks with adjustable spring perches, like can be had from GAZ. I have gone the spacer route and am please with the results.
Rear bar: unless you are adding an OEM XJS rear bar, you will want to change the front bar before adding a rear bar. The after market rear bars are pretty thick, and need a thicker front bar to be used in tandem, so as to not adversely affect the under/over steer situation.
I have the ADDCO front and rear bars on my car, and I really like the result. I DO have to watch carefully how I apply power around curves, and especially in the rain around curves, as the rear will come out quickly. Most track cars (E’s and XJS’s) do not use rear bars, favoring judicious choices of spring rate and damper properties. But for all around street driving, I much prefer the car with the uprated front and rear bars.
M
… favouring judicious depression of the right foot instead… 
I was once followed by a mate of mine around a long sweeping corner, admittedly I knew it well, but he struggled to keep up. I was in my XJR-S (old, but with suspension mods as above), he was struggling, in a new BMW M3 CSL.
Cosmo:
I’ll bet you had a lot of fun on that one!
I suspect that you would find that a car with F/R bars and other bits in good order would be reasonably formidable, too.
A well tuned rear cage (spring rates, dampers, again) would probably be the better way to go, but also probably more costly to do (better quality, adjustable dampers and custom springs, I would wager). You’d still want a heavier bar in front, regardless.
On my car, I have taken the ride height numbers of the XJS-R and matched them, and am using 40 series 17" tires on the front and 50 series 17" on the rear, so the car has that slightly nose-down attitude of the XJS-R. All of the changes substantially improved handling, at the cost of losing some of the Jag magic carpet ride, but in any case, not a rough ride, regardless: firm, and one does feel bumps one did not before, but it is not harsh. The car is a convertible, and these don’t respond well to excessive stiffness and shock rate.
I really like the result, and yes, that unsuspecting bimmer pilot who wants to play will often end up rather shocked, kind of like yours was.
These cars are remarkably competent, especially when dialed in a bit more.
Mike90,
Did you use different suspension bushings? If so, what?
My biggest fix on my 91 conv was the HB front “X” cross bar & aftermarket F&R sway bars. I think the back 3/4" & front is 1". I also did the other usually lot of Poly bush’s, shocks & springs.
Looks like SNG sells the Eibach springs, i may look into them next year. Firmer, and 1" lower.
Who or what is “HB”?
B stands for Bailey, not sure but I think H is Harvey Harvey Bailey
HB is Harvey Bailey in England . Early xj-s conv had a problem with front end shimming around 60 mph. I really don’t know if there ,HB, are even around.
Thanks. There is still a shell of a website, but not much there. The crossbrace was for convertible models from what I can tell. I have a coupe.
Just an FYI, that the front ADDCO bar is back in stock. I’ve been watching for a year for it to be available again.
I have the rear already.
Rob
My understanding is the coupe didn’t have this “shimmy problem”, just the pre 92 conv’s. But don’t know this for sure. I also believe Jaguar recognized this problem & installed a similar “X” brace on post 92’s, but again I’m not sure. The HB X brace was expensive,over $300 with S&H from UK @ 20 years ago prices . But could very well be made if someone had one to copy from with readily available materials & welding skills for MUCH cheaper.
Front suspension was rebushed with poly. After a period of squeaking, it calmed down. I also use poly bushes in the rack mount- vastly more precise steering feedback.
On the rear, I rebushed with factory, including cage mounts. The big end radius arm bushes were rotated 90 degrees to locate the slots parallel to main axis of car. I had looked a poly for the large and small ends, etc. but research on the list showed a sharp divide on whether advisable to do this. Some pointed to the fact that the stiffer compliance led to more cage motion, and rear steering. I paid attention to this, as when I got the car, the cage mounts were in bad shape (too much compliance, effectively!), and the car was REALLY squirrely in sweeping high speed turns on the freeway…I replaced the cage mounts and this went totally away. Anyway, the discussion led me to cast a wide glance at poly for the rear.
I should mention, I run a 5 speed, against a 3.54 diff, and fore and aft cage motion is something to pay attention to. I have had to replace one set of radius arm bushes due to the torque that can be quickly generated with this setup. To address this, I have acquired a ladder frame from an XJSC, which I intend to install with a pair of big end radius bushes attached to the diff tie plate and this frame. This should tighten up the car (convertible) a bit more, and limit the fore and aft tilting of the cage under heavier than normal throttle.
More than you asked, but…I figured you may want to know the picture.
M
Thanks to everyone who’s replied. I’m rebushing the front with OEM bottom bushes and poly uppers, and with poly rack mounts. I’m considering poly front subframe mounts with stock front subframe rear mounts. In the rear I plan to use new trailing arm bushes, with front 90 degrees rotated. May use poly for rear trailing arm bush at the cage. I intend to use the stiffer rear cage mounts from SNG Barrett.
I have a set of Addco f&r sway bars that will be going in. I’m running wheels from an XK8 with wider tires.
jal5678:
You may want to consider reversing the OEM and poly choice locations on the front. I say this because the tops can be done without having to compress the springs and undo the pans to change the lowers. Plus, you gotta get those pivot shafts out and they can be a bitch, both to get to and to drive out. If I could have located delrin bushes for the lower bushes, I’d have used that it instead, so badly mangled were my OEM originals at the lower A arms.
After driving it, I probably would only do poly on the lower A arms, the rest, OEM rubber. Poly made the suspension firmer, but that didn’t do all that much to the handling. At least it fell short of my expectations.
On my car, those lower bushes were trashed, and that is why I rebushed the front suspension. And the metal sleeves bonded to the rubber had corroded onto the pivot shafts. So I had to douse them in PB BLASTER over several days before attempting to drive the shafts out.
More fun than I should have been allowed.
My 2 cents.
M