Clunks
If something in the front goes "clunk" when you drive over a bump,
check the rubber bushings on the top of the front shock absorbers.
British non-metallics again. Any generic rubber shock bushing will
do, and will do better than the original.
Front Suspension Check
You may be confident that your front suspension is just fine, but
this test is so quick and easy you might as well try it. Stand beside
the car and grab the top of a front tire and shake it vigorously in
and out. If everything is OK, the only thing you will feel is the
flexing of the tires, and you will hear nothing.
If you feel any slop, or you hear a "clunk" back and forth, your
front suspension is NOT up to snuff. You should check the following
items, which are discussed in more detail below:
- Adjustment of the wheel bearings.
- Condition of the ball joints, upper and lower.
- Wear groove on bottom of front axle.
- Bushings at inner end of upper and lower swingarms.
- Front subframe mounts.
Perform this test and correct any problems noted before having
your car aligned. The repair or replacement of ball joints, tie rod
ends, swingarm bushings or subframe mounts normally requires
realignment, and it's a shame to have to do it over.
It should also be noted that, contrary to common belief, a car
will not periodically require realignment for no good reason. If a
car was correctly aligned at one time and no longer is, it is because
parts are either worn or damaged, and merely realigning without
addressing those parts is unwise.
Front Hub Removal
Michael Neal suggests the brake caliper not be removed when
pulling the hub, to avoid fiddling with the
steering arm shims. Instead, unbolt
the disk from the hub by inserting a socket through an opening in the
dust shield. Then, remove the hub leaving the disk in place.
Front Wheel Bearings
According to Chad Bolles, the XJ-S uses standard front wheel
bearings, available in any auto parts store. The pre-1977-1/2 XJ-S
outer is an A-2, the inner is an A-6. The post-1977-1/2 car uses A-13
for the inner, A-12 for the outer.
Front Axle Wear
The inner races of the inner front wheel bearings tend to turn on
the axles. As a result, they eventually wear a groove in the axle, on
the bottom where the load is. This allows the wheel to wobble even
when the bearings are adjusted properly, and your Jag starts driving
like a Pontiac. To check:
- Remove the front hubs and check the stub axles for a wear
groove. Run your fingernail along the bottom of the axle from the
upright outward. If your fingernail catches at all, the axle
should be replaced.
- When assembling, ensure that the inner races will not turn by
using Loctite 640 or some similar high-strength bearing retaining
substance. Use it on the inner race of the outer bearing, too,
since it has been known to have the same problem.
- Adjust the front wheel bearings as described below.
Front Wheel Bearing
Adjustment
Spin on the retaining nut until it seats, normally a very sudden
change; continue to tighten while turning the hub until an
increase in resistance in turning the hub is felt. This is usually
about 1/10 of a turn after the adjustment nut starts to seat. This
may seem tight, and in fact may be tighter than the official Jaguar
procedure (measuring end play) would result in. Any bearing expert
will tell you that proper operation of a roller bearing requires some
preload. It is better to be too tight than too loose. When tight, the
weight of the car is distributed among the rollers. When loose, the
slop allows the load to be taken by only one or two rollers at a
time, and the unloaded rollers may slide rather than roll.
Front Wheel Bearing Caps
Apparently, some bearing caps are a total seal, while others have
a small hole in the middle. It is suggested that if you have wheels
that don't keep dirt out of this area, put a small piece of aluminum
tape over the hole. Or, just pry it off and take it down to the local
auto parts store and buy a generic replacement.
Ball Joints and Tie Rod Ends
To test joints such as these, it is helpful to find a convenient
way to "shake" them, or to move them in such a way that will cause
them to slop one way and then the other. In the case of tie rod ends,
this is easily done by moving the steering wheel back and forth just
a little. With ball joints, if the front tire shaking described above
caused a "clunk", that same motion will work for this test.
This test requires two people. Place a single finger on the joint
in question in such a way that one side of the finger is against the
hardware on one side of the joint, and the other side of the finger
is against the other side. While holding this position (may be
difficult, since the car should be sitting on its wheels) another
person should provide the shaking motion. If the joint is OK, no
motion can be felt between the two parts. If the joint is loose, a
human finger will easily detect the slop. Typically, any slop at all
is unacceptable, the joint should be replaced.
Swingarm Bushings
Swingarm bushings may be checked using similar methods as the ball
joints, except that the bushings include some rubber so there will be
some slight motion even in a perfectly good joint. Usually, the best
indication that a swingarm bushing is bad is that some of the rubber
is hanging out of it.
Front Subframe Mounts
If your XJ-S goes "clunk" every now and then, notably when you
first start moving, one of the things you should check is the rubber
mounts that hold the front suspension assembly to the frame. There
are two doughnut-shaped mounts at the front, and two V-shaped mounts
near the steering rack. If the rubber is torn or otherwise damaged,
they should be replaced.
Grease (Zerk) Fittings
Unlike the newer American "low-maintenance" cars, the Jag has zerk
fittings all over the suspension. Periodically it should be gone over
with the grease gun, but please be conservative. It is tempting to
grease fittings too often and to pump too much grease, which will
destroy the seals or gaiters on the joint.
The following is a list of the grease fittings on the car:
- All six universal joints -- good luck getting at the forward
one on the drive
shaft. The protective covers on the rear axle U-joints have
openings for greasing, but they may not line up. You can relocate
them as necessary.
- All four corners of the flat plate under the differential
(lower swingarm inner joints). There are holes in the plate for
access to the zerk fittings.
- The needle bearings in the lower pivot joint of the rear hub
carriers; the fittings are just inside the rear wheels at the
bottom.
- Both front hubs. The fitting is on the side of the hub near
the outer cap. With some wheel designs, the wheels do not need to
be removed. Rumor has it these fittings have been deleted in later
cars.
- Both upper front ball joints -- remove the front wheels for
access.
- Both lower front ball joints. The fittings point inward,
underneath the car.
- Steering rack -- see the note
later in this section.
Also, the rear wheel bearings should be greased by removing the
small cap on the hub carrier and spooning a little grease into the
hole. Don't overgrease, because the excess merely spins out and coats
the inside of your wheels.
The pre-1983 Jaguars also had zerk fittings on the tie rod ends,
but the later cars were fitted with "improved" tie rod ends with no
such fittings.
The ball joint zerk fittings are designed with a relief system to
prevent the grease gun from applying too much pressure. Under the
fitting itself is a plastic washer that covers the relief hole. When
the joint is full of grease, any additional greasing will force the
plastic washer to bend, allowing the grease to come out adjacent to
the fitting itself.
Michael Neal sends this tip on lubricating the lower ball joint:
If the grease comes out from behind the plastic washer as soon
as you apply it then the passage is plugged. The best way to clean
the passage is to remove the lower plate and zerk fitting. Ream out
the passage and apply some grease to the cup before reassembling. The
grease in the passage hardens after a relatively short amount of time
and plugs the passage.
When installing the zerk fittings on these ball joints, note that
overtightening the fitting onto the plastic washer will deform the
washer and open the relief hole.
See the note on lubricating the water pump in the section on the
Cooling System.
Don't overlook the zerk fittings themselves as a possible source
of trouble. Each zerk fitting has a tiny spring-loaded ball check
valve to allow grease in but not out. It is susceptible to corrosion
and jamming. They are also easily damaged by impact.
Anti-Seize Compound
See the description in the
Maintenance Tips. This note
is to point out that many suspension components involve tapered fits,
such as the ball joints and the front axle in the upright. It is
suggested that anti-seize compound be used on the tapers themselves
as well as the threaded nuts. It does no harm, and can make the
assembly much easier to get apart in the future. In these
applications, care should be taken to ensure the entire fitting is
thinly coated, since the anti-seize compound will not be spread
during assembly as it is on threads.
Lower Ball Joints
The original lower ball joint is a rebuildable assembly, with
parts books listing the individual components. The lower ball joint
from the XJ40 (the 1988-on boxy XJ6) is a one-piece throwaway item
(part number CAC9937) that will replace the entire ball joint
assembly on the XJ-S, and costs less than the individual parts of the
original design. In fact, Jaguar no longer makes the original,
rebuildable ball joint or parts to fit it; the authorized repair
shops merely replace the joint with the XJ40 item.
An aftermarket parts company, Quinton Hazell, makes a rebuild kit
for the original lower ball joint assembly. QH's prices for this kit
are much more reasonable than the Jaguar parts prices ever were, and
it is cheaper to use this kit to rebuild your ball joint than to
install the new XJ40 unit.
The lower ball joint is assembled with shims to provide a properly
snug fit between the ball and the socket. However, it should be noted
that these shims are intended to provide a proper fit at assembly,
NOT for removing the slop from a worn joint. If a joint develops
slop, it should be rebuilt with new parts or replaced entirely, not
merely readjusted.
When rebuilding the lower ball joint, don't lose the shims that
come out. Although the QH kit includes shims, they are really
intended to provide some adjustment capability from the original set;
there may not be enough to provide all new shims.
When rebuilding the ball joint, thoroughly grease the ball and
socket parts prior to final assembly. Although the joint has a zerk
fitting, its use is no substitute for proper greasing at assembly.
Ball Joint Gaiter
The gaiter on the original Jaguar ball joint is a Rube Goldberg
assembly in itself. It is a clear flexible plastic item, with a steel
ring molded into it to make the small opening fit snugly around the
ball shaft. The gaiter fits into a plastic ring (C22970), and a
rubber ring (looks like a skinny O-ring) fits into a groove on the
gaiter to hold it snugly into this plastic ring. The plastic ring
then snaps onto the ball joint. Be sure that the plastic ring is
oriented properly; the little ridge on the inside must be on the edge
toward the joint itself.
The gaiter provided in the QH rebuild kit is different than the
original. It is a more conventional solid black rubber item with no
metal reinforcement. A metal clip is provided in the kit to be used
in place of the rubber ring on the large opening. The kit does NOT include the plastic ring; if you boogered up the
original getting it apart, it can be ordered separately. In a pinch,
the gaiter seems to work just as well attached directly to the socket
without the plastic ring.
If you are replacing just the gaiter itself and have neither the
metal clip nor the rubber ring, you can simply tie it on with some
wire. If using the QH gaiter, you can use nothing at all -- the black
rubber gaiter fits quite snugly.
The original Jaguar gaiter has a life expectancy of less than five
years. The clear plastic turns dark brown, then rots and falls out in
crumbs. However, the gaiters in the QH kit are also British, so
there's no telling if they are any better than the originals.
The ball shaft must be separated from the lower A-arm to replace
the gaiter. Disconnect the upper ball joint to allow tilting the
upright to get better access. Use of a fork-type ball joint separator
on the lower joint will not only destroy the old gaiter, but the
plastic ring and the upper ball seat as well. The fork type separator
doesn't work very well here anyway; better to have the screw-type
separator on hand. If the joint isn't jammed too severely, it is also
possible to get the joint loose by disconnecting the tie rod and the
brake line (helpful for getting the nut off anyway), jamming
something between the inner edge of the hub carrier and the A-arm,
and forcefully rocking the hub carrier outward.
Upper Ball Joint
The official repair manual calls for "Steering Joint Taper
Separator JD.24", but we don't need no steenking separator! Put the
car on jackstands and remove the wheel. Put a jack and block of wood
under the lower ball joint and jack it enough that the rubber bumpers
on the upper A-arm are not touching the subframe. Loosen the nut on
the upper ball post several turns, but do not remove it. Lower
the jack so that the rubber bumpers sit on the stops and the full
spring force is applied to separating the joint. If you're lucky and
the previous mechanic used anti-seize compound on the taper, you'll
hear a pop as it comes loose. If more difficult, a little judicious
tapping on the side of the upright may help.
Make sure to note where the shims are located between the arms and
the ball joint. Even if you plan to have the car aligned, at least it
will drive better on the way to the shop. The shims are supposed to
lift right out, but they weren't made quite right. They tend to catch
the bolt on the inner corner on the hook-shaped end. If this corner
is filed slightly, reassembly will be easier.
The gaiter and associated parts on the upper ball joint are
exactly the same parts as those on the lower joint -- see notes
above.
Steering Arm Shim
The steering arm bolts to the hub carrier with two bolts. At the
rear (longer) bolt, there is a shim (it looks like a washer) that
goes between the steering arm and the brake caliper. Don't lose
it! Omitting this shim at reassembly screws up your alignment and
distorts your suspension parts.
If you have lost the shim already, replacements are available in
0.004" and 0.010" thicknesses. To determine the thickness required,
assemble the parts and tighten all bolts except the one the shim goes
on. Measure the gap between the brake caliper and the steering arm
with a feeler gauge. After assembly with the appropriate shims, be
sure to have the car aligned.
Front End Alignment
Randy Taylor 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.
There are reports that the spec books that alignment shops have
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.
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
Steering Wheel Alignment
If your steering wheel is cockeyed when driving in a straight
line, your problem may be in the relationship between the steering
wheel and the rack, or between the rack and the wheels. Jaguar has
provided a nifty method of determining which. If you remove the
grease fitting from the steering rack, a dowel (or special Jaguar
tool no. 12279) can be inserted to engage a notch in the rack. When
the notch is lined up with the grease fitting hole, the rack is
centered. The steering wheel can then be lined up properly. Once this
is done, a misalignment when driving straight (be sure you're on a
level road, and not in the right lane of a road that is crowned)
calls for correction at the tie rods. If the correction is minor and
you are confident that the alignment is otherwise OK, this can be
done by carefully marking both tie rods and adjusting both of them
the same amount.
Ride Height
XJ-S owners are often concerned about whether the car is actually
supposed to sit that low, or if something is wrong. The Jaguar XJ-S
Repair Operation Manual describes a check, but it assumes you have
original tires with full tread. It also assumes you have "slip
plates", devices you set the front tires on so they can slide around
and not bind the suspension travel. The following is a derived
procedure that subtracts the tire rolling diameter out of the
equation in order to determine if your car is sitting at the
"correct" ride height for the tires you have on it, and all it
requires is a level section of concrete.
Position the car on level ground with nobody in it, no heavy stuff
inside or in the trunk, a full tank of gas, the emergency brake off
and the shifter in N. Push the car back and forth a few feet. When
pushing rearwards, push on the front bumper and deliberately bounce
the front of the car a little while pushing. When pushing forwards,
push the rear bumper and deliberately bounce that end as well. This
is to make sure the car is fully settled in its position.
Measure the height to the center of the front wheels. With any
luck, they should be the same, but if they vary slightly determine
the average.
Subtract 6-3/8" from this height. This gives you the correct
height above the ground for the flat bottom of the cross member
between the front wheels.
Using the same front wheel center measurement (do NOT measure the
height of the center of the rear wheels), subtract 4-7/8." This will
give you the correct height above the ground for the edges of the
plate between the rear wheels with a full tank of gas.
So much for the "correct" ride height. Now, to describe what you
actually have, a story from B. J. Kroppe:
My former supervisor (a Jaguar employee) did vehicle packaging
for the F-Type. He started with XJ-S drawings and came across some
things which didn't add up. So he went to the assembly plant and
measured some XJ-S vehicles and compared them to the drawings. He
discovered that the cars being produced (this was mid-late 1980's)
were very much lower than the drawings said they should be.
After some investigating he learned that over the years more
features had been put on the car, making it heavier, but springs had
not been changed to accommodate for the added weight, thus causing
the lower ride height in the actual cars vs. what the drawings were
saying.
In practice, it appears the XJ-S may ride about a half inch lower
than the "correct" ride height, even when new. If yours is
significantly lower than that, however, it's probable that either the
shocks or the springs need replacing.
Sagging Front End
If your Jag seems to be riding low on the nose end, a likely
culprit to check is the front shock absorbers. The XJ-S uses gas
shocks, in which the damping fluid is held under pressure by a small
amount of gas within the chamber. A side effect is that the pressure
causes the shock to try to extend. This extending force helps raise
the car a little, especially when the suspension is soft. The Jag was
designed for these shocks, and if they lose pressure, the nose sags.
Since the pressure may be lost while the fluid is still present, the
low nose may be the first sign of failing shocks. Of course, the rear
shocks are also gas type and may cause the same problem, but it
doesn't seem to happen as often.
Shock Absorbers
The mail-order catalogs seem to offer only original shocks or
big-bucks performance shocks. However, NAPA, Monroe, and Gabriel
offer serviceable, reasonably-priced gas shocks for the XJ-S.
To check the front shocks, jack up the car and remove the front
wheel. From inside the engine compartment, remove the locknut, nut,
rubber doughnut and seat from the top of the shock absorber. Then
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 front shocks should be checked before having the car aligned.
The front end of the car sitting lower than it should has an effect
on the camber, and will alter alignment settings.
Steering Column
Installation
If you have lowered your steering column, Rob Reilly sends this
tip for reinstallation:
When putting back the steering column use a little rubber
cement to hold all the washers in place. Leave the bolts loose and
pull the column back about 1/4" before you tighten them; if you
don't, you will get binding in the lower column universal joint and
bumpy steering.
Steering Rack Lubrication
According to the John's Cars
catalog, using the zerk fitting on the steering rack does more harm
than good, and they remove them during their rebuilds. Others have
reported no problems, but obviously one would be well advised not to
get carried away with the grease gun.
Steering Rack Lowering
Any time the steering rack is lowered for inspection or repair, it
is wise to disconnect the bolts mounting the power steering cooler to
the subframe. The pipes on this unit are very fragile, the hoses are
short and often stiffened by age and heat, and a new cooler is of
course more than US$100. It can generally be repaired by any
reputable radiator shop, however.
Steering Rack Mount
Bushings
The mount bushings in the steering rack are parallel to the axis
of the rack itself. Since the forces caused by steering are also
parallel to the rack, the elastomer in the bushings is subjected to
shear. This is a really lousy design; sound engineering practice is
to avoid shear or tensile stresses in elastomers, and subject them to
compressive loads only.
This book is organized such that this section covers maintenance
only, modifications are later in the book. Many people probably feel
that they do not wish to modify their car, and may not even read
through that section. Please, PLEASE, go to
the section on Suspension & Steering
Modifications and take the advice on replacing these rack mount
bushings. Even if the stock bushings have not yet failed, even if the
car is brand new, it is advised to replace them with alternative
design bushings.
Contrary to the instructions in the manual, the steering rack can
be lowered far enough to work on the mount bushings without
disconnecting either the hydraulic lines, the tie rods or the
steering column. The only difficult part is access to both ends of
the three mounting bolts.
John's Cars offers a rental tool
for removing the original bushings from the rack. It is extremely
helpful, especially when working with the rack hanging under the car
where a bench press won't help. Or, you can improvise such a tool
using two 3/8" drive sockets (one deep), a long 5/16" bolt or piece
of threaded rod, and nuts and washers.
Be sure that all rack mount parts fit snugly when assembled. Do
not use the bolts to pull the frame in to meet the sides of the
bushings. If necessary, buy some 5/16" fender washers and insert them
alongside the mounts to make them fit properly.
Steering Rack Mount Bolts
If you happen to be working on the rack with either the engine or
the front subframe out of the car, you may be able to put the bolts
in any way you wish. But for the benefit of those who work on the car
later, please install the upper mount bolt on the driver's side from
the outside inward, and the lower bolts on both sides from the inside
outward. This makes it much easier to install or remove the rack with
the engine and front suspension in the way.
If you must replace the mounting bolts, be careful not to use
bolts that are too long. When complete, be sure the upper bolt on the
driver's side does not protrude too close to the engine block, since
the engine moves on its mounts and will beat against the bolt. And
the lower bolts should not protrude too closely to the lower A-arms,
since they are likewise mounted on rubber and may move during
operation.
Steering Rack Removal
If you have to remove the steering rack, one problem is how to
remove the pinch bolt that connects the steering column swivel joint
to the tower shaft. Remove the oil filter first, then turn the
steering wheel until the pinch bolt is positioned where you can get
at it.
Also note that the pinch bolt must be completely removed for the
swivel joint to be disconnected from the tower shaft. The tower shaft
has a recess the bolt fits through; merely loosening it will not
permit removal.
Steering Rack Tower
Shaft Seal
This seal is prone to leakage. John's Cars offers an aftermarket
seal that is supposedly better than the original. It better be, it's
quite expensive.
Reportedly, one problem associated with this seal is incorrect
installation by driving it too far into the housing. Be sure not to
drive it any deeper than it needs to go.
Steering Rack Rebuilding
There is a "seal kit" available for the steering rack. Note that
reportedly the tower shaft seal is NOT included in this kit; check
with your source and order the tower shaft seal separately if
necessary.
A high percentage of people who have rebuilt their own steering
racks have reported failure on the first try, and all for the same
reason: when installing the rack bar through the seal on the driver's
side end of the rack, the teeth on the rack bar ruined the seal. This
typically results in ordering an entire new seal kit to obtain this
one seal, and greater care the next time. The repair manual calls for
wrapping the rack with tape prior to sliding the seal over it;
apparently this is the minimal precaution, experience says to lube it
up as well and exercise extreme caution during assembly. It has also
been suggested that the seal and the part it mounts into be slid over
the rack separately and then assembled, since installation in the
housing makes the seal more difficult to work with.
Power Steering Pump
The XJ-S power steering pump is a standard GM Saginaw unit.
However, it is uncertain whether the Jaguar system operates at the
same pressure as a GM; so, if you replace the original unit, it is
suggested that you remove the pressure control valve from the Jaguar
unit and install it in the new one. The pressure control valve is
easily removed by removing the outlet fitting and shaking the unit
until it falls out.
Power Steering Fluid
You're supposed to put the same type fluid into the power steering
unit that you put into the automatic transmission. This is
interesting, since the early cars with the Borg Warner automatics
called for Type F fluid while the later cars with GM 400 automatics
call for Dexron II/III, and the power steering system didn't change.
Apparently any ATF will do in the power steering system.
Apparently Type G fluid was called out in some owner's manuals for
the power steering. "Type G is an obsolete designator for Dexron.
It's so obsolete that nobody remembers what it was."
See the discussion on Dexron ATF's in the
Drivetrain section.
Rear End Alignment
There's no such thing as castor on non-steering wheels, and toe-in
is not adjustable on the rear of the XJ-S; if it's off, something is
bent. The only alignment adjustment available at the rear is the
camber, adjusted by replacing shims between the inner end of the axle
and the brake disk. The more shims put in, the more the top of the
rear wheel tilts outward.
Note that there are usually some shims between the brake disk and
the differential unit. These are to locate the disk properly between
the calipers, but also affect the camber as well. If working in this
area, always make sure all shims are reinstalled properly.
Randy Taylor offers this advice:
Camber is not a constant. The camber control is taken on two
pivoted arms (of unequal length) so that the camber can change on a
predetermined curve based on suspension position.
It is very unlikely for the camber to change from factory specs
unless one of three things happens: either something is bent, someone
left some shims out during a differential or brake service, or the
ride height is wrong. The #1 cause is the last: sagged rear springs.
So, when you are told that the rear camber is off, investigate the
static ride height before investing a lot of time/money in shim
swapping.
Rear Suspension
Subframe/Differential Removal
To work on the differential, as well as many major tasks relating
to the rear brakes, it is necessary to lower the entire rear
suspension assembly out the bottom of the car. Fortunately, this is
nowhere near as difficult as it appears. Jan Wikström says:
You need two good stands and a small garage jack, as well as a
friend to stabilise the subframe as you move it down and up (and help
you lift it to the workbench; that sucker is heavy). To make the job
a lot easier, take the spring/shock units out first and refit them
last. You'll need to shift the subframe in two lifts, as the stroke
of the jack won't be long enough. I use a 5" thick wooden block on
the jack and rest the unit on two cement blocks halfway up.
Some others have reported good results with putting the wheels
back on during removal; that way, the assembly can be rolled out from
under the car. It will require positioning the car on even taller
stands, though.
Rear Spring/Damper
Disassembly
The obvious way to disassemble the springs from the dampers on the
rear end is to remove the damper with the spring installed, then use
a spring compressor on the bench to separate them. However, Ian
Macfarlane provides an alternative procedure:
To change the rear shock absorbers without using a spring
compressor, the springs can be held in the compressed state by
fitting four elongated "C" shaped brackets (two per spring) over the
centre 80% of the spring with the car jacked up under the suspension
(preferably with a load in the rear of the car to maximize spring
compression). Then, when the car is jacked up under the body, the
springs will remain partly compressed and the shock absorbers can be
replaced relatively easily.
Rear Wheel Bearings
According to Chad Bolles, the bearings in the rear wheel carriers
are a Bower/BCA part number 18590-18520 for the inner, and
18690-18620 for the outer; available in any auto parts store.
Rear Axle Failure
Jan Wikström reports on his problem and solution:
The stub axle in the hub carrier (the bit that turns in the
rear wheel bearings) is splined for the hub and has a large thread
and castellated nut on its outer end. This thread comes right down to
the splined part with no fillet whatever and creates a horrendous
stress concentration at the end of the thread. Mine suffered a
fatigue fracture in consequence; my local parts pusher tells me this
is not uncommon, as one would expect from such an elementary error,
especially if the nut is overtightened. Accordingly, I ground and
polished a shallow rounded groove at the base of the thread of the
new part... (see Figure 3 and Figure 4, illustrations graciously
provided by Jan Wikström).
Figure 3 - Rear Stub Axle Failure Location
Figure 4 - Rear Stub Axle Modification
The next time you do the rear wheel bearings or U-joints, I
strongly recommend having the stub axles checked and modified; any
competent engineering shop will know about stress relief. Modifying
parts of the Jaguar may be sacrilege to some of us, but fine as the
design is, it isn't perfect...
If the stub axle has already broken, it is possible to fix it by
drilling and tapping a hole in the end and using a bolt and washer
instead of the nut. GT Jaguar offers
a grade 8 bolt and a specially designed washer for this purpose,
although you could conceivably come up with suitable parts from local
sources. This fix may also be used as a preventative measure, since
cutting off the stub and drilling for the bolt eliminates the stress
concentration in the original part as well as the shallow groove
does.
Perhaps one thing to note is that
GTJ offers these parts at all; that
would seem a serious indicator of just how common this problem is,
and how important it is to address it.
Rear Hub Carrier Cracking
Joe Bunik reports that the cast aluminum hub carriers on his car
cracked in the area just above and outward of the fulcrum shaft. The
crack was parallel to the fulcrum shaft, but just far enough above it
to be in the structural portion between the fulcrum shaft bearings
and the wheel bearings. According to his mechanic, this is not an
unusual problem.
Folks, if this part breaks at speed, you will be
taking the Lord's name in vain! These parts are expensive, but if a
crack is found one would be foolish indeed not to address it.
What with the rough surface on the cast aluminum combined with the
dirt and grime normally covering it, it is entirely too easy not to
notice a crack like this. Whenever a rear wheel is removed, it is
recommended that the hub carrier be cleaned up a little and inspected
for cracks, especially in the area just above the fulcrum shaft.
Spoke Wheels
Yes, a Jaguar with real spoke wheels really looks good.
Unfortunately, it generally doesn't drive worth a hoot. The spoke
wheels available have a reputation for trouble. Spoke wheels were a
good idea in the 1950s when Jaguars needed to maximize air flow to
cool their brakes. Since that time, two changes have conspired
against spoke wheels:
- The advent of tubeless tires. Many spoke wheels won't
work with tubeless tires, so you must install a tube. A tube
installed in a speed-rated tire (the XJ-S should be fitted with
V-rated tires) completely negates the rating, and renders the tire
unsafe at speed. Don't drive fast with inner tubes in your tires!
- The advent of low, wide tires. A spoke wheel is a
reasonable structure when it's tall and skinny, like a bicycle
wheel or the automobile wheels of the 1950s. But it is a
structurally poor design for modern low, wide wheels.
Furthermore, modern Jaguar wheels need an offset (distance from
mounting surface to centerline of wheel) of around 1-1/2" which is
not conducive to spoke wheel strength.
Maintenance
Spoke wheels tend to need truing on a regular basis. This is not a
job for the home mechanic, and finding someone who can do it is a
challenge. Often the wheels must be returned to the manufacturer for
truing. Obviously, whoever does it, this process will also require
rebalancing because the wheel is not the same shape as it was.
Rust Problems
Spoke wheels generally have chrome-plated steel rims, leading to
rust problems, flaking chrome, and associated leakage at the tire/rim
seal.
Weight
By the way, if it's a weight reduction you expect, forget it.
There is nothing lightweight about spoke wheels.
It should also be noted that since the spoke wheels are more
flexible than alloy, the handling will suffer somewhat. With a car
this heavy, the difference in the way the car corners is noticeable.
You may even get sounds, as the spokes strain and creak with the
load.
Alloy Wheels
The specified torque on lug nuts on earlier Jaguar alloy wheels is
45-50 ft-lb., and 75 ft-lb. on later ones. This impresses some people
as not being very tight. However, higher torque is unnecessary and
causes damage to the aluminum wheels; this is true of all alloy
wheels, and in this day and age your tire store should know better.
If the shop installs your wheels with an air wrench, tell them where
to get off and take your business elsewhere.
There are now machines in better tire stores that mount tires by
gripping the wheel from the inside with soft grippers and never touch
the wheel's pretty outside surface. Check out the price lists for new
Jaguar alloy wheels and decide for yourself if it's worth finding a
store with this equipment.
You might also want to watch how the wheels are mounted on the
balance machine.
Anti-Seize Compound Again
Believe it or not, one of the places where Jaguars are known to
have seizing problems is between the alloy wheel and the hub. Robert
Woodling suggests use of anti-seize compound on the mating surfaces,
especially at the hole in the center of the wheel. It can be
disconcerting to have a flat tire and be unable to get the wheel off.
Wheel Balancing
Incompetence is rampant in the retail tire industry -- at least in
Florida. Left to their own devices, most of the meatheads in a tire
store will happily static balance your Jaguar alloy wheels, then beat
the weights onto the rim with a hammer.
Static Balance
There are two basic types of imbalance. The old-fashioned bubble
balancing, which engineers refer to as static balancing, only
corrects one type of imbalance -- the type that causes the wheels to
hop. This is generally adequate only for wheels that are very narrow,
and should be considered unsatisfactory for any modern automobile.
Dynamic Balance
The other type of imbalance, dynamic imbalance, is the type that
causes wobble. A wheel that is statically balanced may still be
dynamically imbalanced by having a heavy area on the outside edge of
the wheel and an equivalent heavy area 180 degrees away on the inside
edge. Although the wheel would appear balanced on a bubble machine,
when spinning the two diagonally opposite heavy areas cause the wheel
to wobble. It's usually not too noticeable on the rear wheels, but on
the front wheels it can cause steering wheel shudder. And you may
eventually want to rotate the rear wheels to the front, so it's kind
of nice to have them all correct.
To correct a dynamic imbalance requires that weights be placed in
two separate planes -- usually (but not necessarily) the inside and
outside edges of a wheel. It requires more lead than static
balancing. It also requires a machine that actually spins the wheel;
the bubble balancer is out. Use of these machines has come to be
called "computer balancing." However, note that a switch on the
machine allows the operator to specify a static balance only, so
asking for "computer balancing" does not guarantee a proper dynamic
balance.
The meatheads generally understand that the owner of alloy wheels
is not thrilled about balance weights on the visible outside surface
of the wheel. The standard response is simple: he sets the balance
machine on "static" and applies all the balance weights to the inside
rim of the wheel. This actually makes the dynamic imbalance worse,
since even in the days of the bubble balancer the operator knew to
put half the weight on the inside edge and half on the outside.
Insist on watching what is going on. There is a button marked
"static" usually at the top left on the machine, with a red indicator
light. When on, the machine will read imbalance values on the left
indicator and a blank display on the right indicator. If you see this
happening, I highly recommend you have your wheels put back on your
car and take your business elsewhere.
The balance weights needed are part of the problem. Steel wheels
commonly use "clip-on" weights that are hammered onto the rim. Some
alloy wheels are designed with a rim that can accommodate clip-on
weights, but they may not attach as well to the thicker aluminum. And
use of a hammer to install is not good for aluminum, especially if
the meathead responds to difficulty with a bigger swing.
Clearance
When the steering on an XJ-S is turned full lock, the clearance
between the inside edge of the wheel rim and the front anti-sway bar
is very small. If wider-than-original wheels are used, clip-on
balance weights may actually hit the bar, resulting in a
blip-blip-blip as you roll around a tight turn.
The proper balance weights to use on alloy wheels are called
"stick-on" and are attached to the inner surface of the wheel with a
layer of foam tape attached to the back side of the lead weight. One
problem is that they are not reusable; once peeled off, the tape is
not reusable, and the shops customarily throw them away. I guess
using generic foam tape has not occurred to them, or just isn't worth
it, even though they often complain loudly that these weights are
expensive and charge the customer accordingly.
The problem is exacerbated by the meathead not knowing how to use
the machine properly and having to do a by-guess-or-by-gosh balance
job. With the clip-on weights, he can just keep prying them off and
reinstalling them until he gets it right, but he can waste a lot of
stick-on weights. An intelligent operator, of course, will be able to
set the machine up properly and get the correct weight applied the
first try.
The older computer balance machines were really designed for steel
wheels. They have a setting for the width of the wheel and assume you
will be putting clip-on weights on the edge. While the machines have
a setting labeled "Mag", it is unlikely the operator will know how to
use it. If you are using stick-on weights (which are located radially
inward and on different planes than clip-on), the machine must be set
up properly in order to read the correct amount of weight required.
Simply setting the same width, offset and diameter info as used on
the steel wheels will indicate if the wheel is imbalanced but will
give incorrect data on the size balance weights needed, so the
operator will be making several attempts.
There are newer balance machines that better accommodate alloy
wheels. They can properly balance the tires by applying weights in
any two planes, not necessarily the outer edges; the desired location
for the weights is a separate setting in the balance procedure. They
also can "split" a large balance weight requirement into two smaller
weights, telling the operator where to put them both. This is helpful
for two reasons: first, a large stick-on weight means a LONG stick-on weight, and as it curls around the rim
its effective radius reduces somewhat, and the balance becomes
inaccurate. Second, using two smaller weights may allow the operator
to hide them behind spokes on some wheels.
Owners of alloy wheels should always insist on dynamic balancing
using stick-on weights in two planes within the wheel -- one near the
inner edge, and one just inside of the outer face of the wheel. Since
these planes are closer together than the edges of the wheel, even
more lead will be required to correct imbalances. But the weights
won't show, and nobody will need to use a hammer to install them.
Always insist that the balance machine shows 0.00 on both indicators
before the balance is acceptable.
The only real problem with stick-on weights is a reputation for
getting lost. Since clumps of mud and other debris sometimes gets
dragged around the inside of the wheel, the foam tape can be ripped
away. Two suggestions are in order, and neither is likely to be done
by the tire shop, so the owner should bring the materials necessary
and do them himself while the wheels are off: First, mark the
locations of the stick-on weights with a permanent marker. Then,
secure them with a piece of aluminum tape (available at air
conditioning shops). Duct tape is not good; it quickly dries up and
falls off, often taking the balance weight with it. The aluminum tape
appears to be light enough to not affect the balance when added.
Wheel Interchangability
A few years back when Jaguar introduced the Anti-lock Braking
System (ABS), they also introduced the new faux spoke pattern alloy
wheels. Some reports at the time suggest these changes were related;
apparently, the older wheels (a domed 5-spoke alloy design)
interfered with the ABS hardware. The bolt pattern, offset, width,
and other dimensions remained unchanged, so the later wheels can be
used on earlier cars. But if the reports are true, the earlier wheels
cannot be used on later cars.
Tires
When replacing tires as a set, you don't have to stick with the
brand of tire that came on the car. In fact, it may be better to
change brands according to Michael Neal, who works on Jaguars for a
living:
I've seen hundreds of the 215/70 Pirelli P5s rip out at the
sidewall near the bead. These are the original equipment tires on the
U.S. spec XJ6 Series IIIs and early XJ-S. Sorry, but I would not even
consider buying a set of these. The 235/60 P600s had the same
problem.
Speed Rating
You should insist on at least a V-rating (a speed rating of 220
Km/h, or 137 mph) unless you always obey the U.S. speed limits. In
some countries, you are required by law to use V-rated tires on these
cars. You will find V-rated tires expensive. The rating is either
indicated within the tire size, as in 215/70VR-15, or
elsewhere on the sidewall, as in a 98V adjacent to the tire
size. Other ratings include S (180 Km/h or 112 mph), T (190 Km/h or
118 mph), H (200 Km/h or 124 mph), and Z (250 Km/h, or 155 mph), and
new speed ratings higher than Z seem to be introduced on a regular
basis. In the U.S., if there is no indication of speed rating, the
tire is S-rated.
These ratings are intended to indicate suitability for
Autobahn-style driving -- continuous high speed. Generally, the
limiting factor is heat buildup in the tire. High-speed-rated tires
either run cooler or are made of higher-temperature material, or
both. Much of the heat generated is dissipated to the air inside the
tire and away through the rim, so inner tubes invalidate the ratings
(the flexing of the inner tubes themselves adds to the heat
buildup).
Since the flexing of the tire is what generates the heat, tire
manufacturers usually achieve a high speed rating by making the
sidewalls stiff. Therefore, the high-speed-rated tires drive
differently than normal tires, even at low speed. For this reason,
many recommend the V-rated tires even to those who don't drive fast.
This is especially true for the XJ6 and XJ-S, because the soft
suspensions get downright mushy with the softer, lower rated tires.
There are reports that S-rated tires used on these heavy cars will
flex so much that they will wear out quickly.
The heat buildup due to tire flexing is also the reason you must
have fully inflated tires when driving fast, as indicated in the XJ-S
glovebox.
As the tread wears, the speed rating of the tire will actually
improve. A thinner carcass generates less heat when flexing, and
dissipates heat better. There have been promotions claiming street
tires were successfully used for racing; in these cases, typically
the outer half of the tread was shaved off before the tire was even
put on the car.
Tire Design
One other thing to consider when replacing tires is the intentions
of the tire design. The original Pirelli P5's were designed for a
soft ride, and the 235/60 Goodyears fitted to the later XJ-S
reportedly also provide an excellent ride -- actually an impressive
achievement when maintaining a V rating. However, most V-rated tires
are designed more for performance than ride, and replacement with
such tires is likely to result in vastly better performance and road
feel but a less luxurious ride. A set of Dunlop SP Sport D40 M2
235/60-15's (unidirectional tread, max pressure 44 psi) convert the
XJ-S from a luxury coupe into a GT. Similar results have been
reported with Yokohama performance tires.
Tire Codes
For those who'd like to know, the rest of the tire size code works
like this: The first three digits, such as 215, is the width (mm) of
the tire at the widest point -- the middle of the sidewall. It is
always rounded to a number ending in 5. The two digits after the
slash, along with an implied decimal point, gives the aspect ratio:
the height of the tire above the rim divided by the width described
above. For the 215/70VR-15, this is 0.70. If there is no such number,
the aspect ratio is 0.80. The R in the tire size merely indicates it
is a radial tire; it is sometimes omitted. The -15 indicates it fits
a 15" wheel.
Overall Diameter
The one thing you normally don't want to change is the overall
diameter of the tire, since this would affect your speedometer and
odometer readings as well as your ride height. Changing the ride
height can have adverse effects on the suspension geometry, even if
you don't mind the altered ground clearance. To maintain overall
diameter when you go to a wider tire, you also have to change the
aspect ratio to a lower value. Tire manufacturers also usually list a
"loaded radius", the distance from the ground to the center of the
wheel with weight on it. This measurement is meant to include the
deformation of the tire under load so the consumer can determine the
actual ride height.
The early XJ-S was fitted with 215/70VR-15, and the later models
with 235/60VR-15 tires. The later tires are slightly smaller in
diameter than the earlier, but there is no indication that Jaguar
altered the speedometer or suspension. Both sizes are very suitable
for the car, and there is normally no reason to select tires beyond
these sizes.
Mixing Tires
DO NOT mix tire types, sizes or makes on a
Jaguar. The XJ-S and the XJ6 have a suspension design in which the
entire suspension assemblies are attached to the car with flexible
mounts, and the relative stiffness of the mounts is premised on all
the tires being the same. Mixing tire types, even outwardly similar
ones, can result in dangerous instabilities in this suspension
system. This is no joke; having one type of perfectly good tire on
one end and another type of perfectly good tire on the other can
result in you being rudely introduced to a tree when you aren't even
traveling that fast.
On to the Body