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reach into the wheel well, grab the top portion of the shock and pull it downward. If it is in good shape, it should move
downward smoothly with a hiss, and when released should move smoothly but forcefully back to its full extended
position by itself. If the motion is not smooth, or the shock compresses easily and quickly with no damping effect, or
fails to extend itself when released, replace the shocks.
The traditional tests of shock absorbers involving pushing the car down and noting its recovery or noting the car’s
reactions over bumps are not entirely applicable to modern gas shocks. If a gas shock loses its gas charge, it may still
appear to pass these tests; if it still has fluid in it, it will still provide some damping. The damping effectiveness is
greatly reduced, however, and will get much worse over a series of bumps. And, as noted above, the car’s ride height
will be affected. There seems to be no substitute for disconnecting the shocks and checking them by hand. Checking
the rear shocks will require a spring compressor to remove the springs from the shocks.
The original shocks on the XJ-S are Boge. Shocks are also offered by Unipart, Spax, Armstrong-Girling, Bilstein,
Monroe, Gabriel, KYB, and Koni, some of which are actually reasonably priced. The only consistent reports received
by this author regard the Gabriels -- consistently negative. They should probably be avoided, despite their lifetime
guarantee.
Monroe, sold by NAPA and many other auto parts outlets in the US, used to offer reasonably-priced, serviceable
shocks for the XJ-S. However, reports are that they came up with the “Sensatrac” design and it went to their heads, and
their prices are no longer reasonable.
Terry’s Jaguar Parts (page 693) offers some “competition gas-filled shock absorbers” with adjustable spring supports
and spherical bearing mounts.
Matthias Fouquet-Lapar points out that Bilstein is now online:
http://www.bilstein.com/
“There is lots of tech info.”
RIDE HEIGHT -- HESS & EISENHART CONVERTIBLE: The H&E seems to ride low even when the shocks and
springs are in good order, especially at the rear. This is apparently because the H&E is heavier than the stock coupe,
but the springs were not altered.
One possible solution is suggested by John Warr: “The shox recommended by Koni for the front of the XJ-S are gas
charged, those for the rear are gas charged, adjustable spring height.” Terry’s Jaguar also offers “competition” shocks
with adjustable spring supports. Coupled with the fact that Jaguar provides shims for the front springs, it may be
possible to set the ride height of both ends where the car looks right.
Of course, another possibility may be to use the springs from an XJ12.
VIBRATION AT PARTICULAR SPEEDS: This is a common complaint with the XJ-S, with owners frustrated that
wheel balancing or other efforts have no effect. Marty Sullivan fixed the problem on his H&E convertible with a
correct alignment; see below. The H&E also has some dynamic absorber weights mounted behind the headlights, so an
investigation of vibrations should include a check to make sure they are mounted properly. Chris Carley, who owns a
’91 (factory) convertible, fixed his problem by replacing “the S-rated Dunlop Qualifier tires 235/60 15 that came new
with car with Yokohama AVS V-rated 235/60 15. Well - why didn't I do this a year ago? The shakes are gone, the car
steers & brakes much better. Also rides smoother and sits at a better ride height. I noticed the shakes were less when it
was cold (read Florida 60ºF), so I can only assume they flexed too much when warm and went out of round?”
ALIGNMENT: First off, note that while many cars are aligned only at the front, the XJ-S requires that all four wheels
be aligned. Although there is really only one adjustment at the rear (camber), it is likely to take most of the mechanic’s
time if any adjustment is necessary; it requires that the driveshafts be unbolted from the differential unit and shims
changed.