Jaguar XJ-S. Manual - part 90

 
 

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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. 

 
 

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Randy Wilson sends a warning to be careful which alignment shop you choose to align a Jaguar:  “The generic 
American tank has shims to align the front suspension camber and castor.  These shims are placed at both the front and 
rear pivots of the upper control arm.  By adding or subtracting shims equally at both ends, you change the camber.  By 
adding or subtracting shims at one end only, you change the castor.  Jaguars do not work this way, but look like they do 
to the uninitiated.  The Jaguar has shims at the upper pivot just like the Chevy/Ford above, but they must be used as 
camber adjustment only with equal amounts of shim change at both front and rear pivots. The castor adjustment is done 
by a separate set of shims at the upper ball joint.  If some hack jumps in there and adjusts camber and castor by 
staggering the pivot shims, you will end up with a car with a sort of correct alignment (dynamic castor gain will not be 
as Jag intended), but the car will just eat upper control arm bushings. 

“The good news is that the XJ front subframe is one stout critter.  Unless it has been seriously whacked, it is rare for 
camber or castor to need adjusting.  Alignment is usually just a matter of setting the toe correctly after the latest steering 
rack change/rebuild.” 

Peter Havas adds, “It is easy to remove the two bolts holding the carrier, and dropping the washers behind the spring 
tower, or confusing the number which go on each side when you re-assemble.  Additionally, I have taken some front 
ends apart which have been re-aligned in the states, and "U" spacers were substituted for the originals to save time.  
These fall right out when the bolts are loosened.”  They also have a nasty habit of falling out when driving; if you don’t 
believe that, just check out how many alignment shims you can find laying on any stretch of road. 

The castor is adjusted by rearranging the shims either in front of or behind the upper ball joint -- but the total number of 
shims surrounding that ball joint should always be four.  Just move them from front to back, don’t remove any or add 
any to the total. 

There are reports that the spec books in the alignment shops consistently list the wrong alignment specs for Jaguars.  
Just to be sure, take your own repair manual with you, and if the numbers that you have disagree with those they have, 
insist they use yours.  They shouldn’t care, it’s your car and your money. 

The XJ-S really needs to be aligned according to the procedures outlined in section 57.65.04 of the ROM -- namely, 
that the ride height must be restrained at a specified position for the alignment.  The standard alignment shop shortcut of 
aligning the car at whatever ride height it sits at is not acceptable; both the front and the IRS geometries change with 
ride height, and many (most?) XJ-S’s don’t sit at the correct ride height by themselves.  Failure to establish the correct 
ride height during alignment may result in a shaking in the front end at 50-60 mph -- a notorious problem in the H&E 
convertible, perhaps because the H&E convertible is also notorious for a low ride height. 

If you’re gonna pay good money for an alignment, you might as well insist it’s done properly.  Of course, it’s not likely 
the alignment shop you choose will have the special tools used to establish the ride height on Jaguars -- unless you go 
to a dealer.  So, if you’re going someplace other than the dealer for the alignment, you’d be well advised to take the 
tools with you -- and the instructions from the repair manual showing how they’re used. 

The tools for setting the ride height of the front suspension are made from short lengths of tubing, and there’s enough 
info to make them provided in section 57.65.04 of the ROM.  The tools for setting the ride height of the rear suspension 
are a pair of metal hooks, and are described only as Jaguar tool no. JD.25.  These would be even easier to make than the 
tubes, if only you knew what the key dimension was -- and just what is this book for, anyway?  Figure 17 should 
provide the info needed. 

 
 

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REAR CAMBER SETTING LINK JD.25

(2 REQ'D)

1" MIN DIA

9 1/32" (229mm)

 

Figure 17 - Jaguar Alignment Tool JD.25 

Note that although the official Jaguar tools are made from a single 9/32” steel rod suitably bent, there’s no reason you 
shouldn’t be able to screw together suitable tools from eye bolts, threaded hooks, threaded rod, and some coupling nuts 
-- all available at any hardware store for peanuts.  Remember that you’ll need to make two. 

These tools might actually be a suitable thing for local Jaguar clubs to keep on hand for the benefit of their members.  
Apparently, these exact same tools have been used on all Jaguars that use the same IRS as the XJ-S -- which means all 
E-types, all XJ6/12 SI/II/III -- basically all Jaguars made for about four decades.  In fact, the dimension shown in the 
drawing was provided by Michel Carpentier, who got it from a Mk10 service manual.  At the time the Mk10 was made, 
the tool was called a J25; the tool names were changed to JD after Jaguar bought Daimler. 

When either end of a Jaguar is being aligned, the ride height setting tools should be in place on both ends. 

In what must be considered a serious shortcoming, the Haynes manual does not discuss this ride height setting 
procedure at all, and lists an incorrect tool number (JD21 -- actually the number for a bushing tool of some sort) 
without going into any detail about using it.  It suggests that alignment is not for the home mechanic, but provides a few 
generic guidelines for what is done -- just enough to get you in trouble.  If you have only the Haynes manual, it is 
recommended that you obtain a copy of the alignment instructions from a Jaguar ROM or shop manual before having 
an alignment done by a non-Jaguar shop. 

Finally, note that most of the above info probably applies only to the pre-1993 XJ-S with inboard rear brakes.  From 
1994 on, a completely different IRS was used with outboard brakes, and it presumably requires different alignment 
procedures. 

If you’d like to try tackling the alignment job on your own, Tony Watts points out that there is a description of how to 
perform your own alignment with simple tools on the WWW at: 

 

http://www.vtr.org/maintain/diy-alignment.html

 

 

ANTI-ROLL BARS -- WHAT THEY DO:  An anti-roll bar (also known as a sway bar, anti-sway bar, or stabilizer bar) 
is simply a spring that resists one wheel from traveling up or down without the wheel on the opposite side moving 
likewise.  For a car to lean, one wheel must go up (relative to the car) while the other goes down, so the anti-roll bar is a 
spring that resists leaning.  This has many benefits, including reducing the shift of the center of gravity caused by the 
leaning, and better traction and tread wear due to keeping the car, and therefore the tires, upright in a corner. 

 
 

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It is a good idea for the roll stiffness to be balanced between the front and rear end of a car.  If one end is stiff and the 
other isn’t, then when the car tries to lean in a corner the outside tire on the stiff end takes all the load while the outside 
tire on the other end takes it easy.  Typically, this will cause the tires on the stiff end to behave poorly and wear rapidly. 
 In general, adding roll stiffness to one end of a car helps the handling of the other end. 

If the front end is stiffer than the rear, then the car tends to understeer, or plow its way through a turn.  This is the 
accepted norm here in the US.  In this case, when the car doesn’t seem to be going where the driver wants it to go, he 
merely turns the steering wheel farther -- a design considered defensible in this age of litigation.  If the car has balanced 
anti-roll stiffness or is stiffer at the rear, there is the possibility that the car will oversteer in a corner -- the rear end will 
swing out.  The correction is to turn the steering wheel in the direction of the slide -- a design considered indefensible in 
court, and possibly exposing auto manufacturers to liability. 

For those who prefer to drive a car rather than have the car drive them, adding a rear anti-roll bar or replacing an 
existing rear anti-roll bar with a stiffer one on an understeering car is a good idea.  The car will have more neutral 
handling characteristics.  Also, there is a more “precise” feel to the steering, even when driving slowly.  In general, the 
car will feel more stable.  And the front tires will usually wear much longer, and wear less on the edges and more 
uniformly across the tire. 

Ah, but what about the ride?  When driving over two-wheel bumps (such as speed bumps), the anti-roll bar merely 
turns on its pivots, and the ride is unaffected.  When driving over one-wheel bumps, however, the motion of the wheel 
over the bump will have a more pronounced effect on tilting the car.  This effect can be quite noticeable.  In cases 
where a series of one-wheel bumps are encountered, the occupant can feel downright jostled, especially if the added 
anti-roll bar is very stiff. 

The above is a very brief discussion of anti-roll bars.  A more complete discussion would include the effects on 
particular types of suspensions, most notably suspensions with shortcomings that an anti-roll bar tends to compound.  
Also, some cars have suspensions with an inherent anti-roll stiffness, and don’t require a separate bar.  However, the 
Jaguar suspension has no such situations, so there is no need for further discussion here. 

Anti-roll bars are customarily described by their thickness, this being an indication of their stiffness.  In general, the 
stiffness of a typical anti-roll bar (solid circular cross section) is proportional to the 4th power of its diameter -- a 1” bar 
is more than three times as stiff as a 3/4” bar!  However, the thickness of an anti-roll bar can only be used for 
comparison against the thickness of another anti-roll bar that mounts the same way on the same end of the same type 
car.  Because of differences in the leverage of the anti-roll bar linkage as well as in suspension geometry and center of 
gravity, a 1/2” bar may be quite stiff on one car while a 1” bar may be barely adequate on another. 

Aftermarket anti-roll bar kits often take advantage of the geometry issue to make their bars adjustable.  While an OEM 
bar typically has a hole or eye at each end where the end links attach, competition models will often have a clevis 
attachment or “slider link” that clamps down anywhere on the end of the bar.  By moving the attachment inward from 
the end of the bar, the leverage is changed making the anti-roll bar stiffer.  You could even move the sliders for an 
autocross weekend and move them back on Monday.  Some wise guys have even figured out how to sell you just the 
adjustable end links that will clamp onto the OEM bar inward of the eye at the end, thereby allowing you to adjust the 
OEM bar stiffer (but not less stiff). 

It’s also worth noting that the anti-roll bar isn’t the only thing that flexes as a car leans into a turn; the inner mount 
bushings, the end link bushings, even the tires themselves all flex, sometimes largely negating the effect of a stiff bar.  
Aftermarket kits sometimes use this effect to provide a sort of poor-man’s adjustability: they will provide end links that 
have springs behind the bushings that allow them to slip a bit before they apply the full effect of the bar.  The result can 
be non-linear, where the anti-roll bar seems very weak at first and then becomes effectively much stiffer after a bit of 
lean. 

It just so happens that this flex issue is critical in the Jaguar XJ-S.  The way the rear anti-roll bar (when there is one) 
attaches to the rear suspension is via attachment points on the radius arms.  However, these radius arms attach to the 
lower swingarms with a very soft rubber bushing.  You can make the rear bar only so stiff before the bar isn’t flexing at 
all, it’s these rubber bushings doing the flexing.  To increase the rear anti-roll stiffness beyond that point, you’ll have to 
replace those bushings with poly or something -- or completely revise how the end links attach to the rear suspension.