Jaguar XJ-S. Service manual — part 101

399

Figure 23 - Rear Swingarm Outer Pivot Assembly w/ Oil Seal

1) Install the outer races.

2) Trial-assemble the center stack using the real fulcrum shaft, distance tube, preload shims, bearings, seal tracks, one

5/8” fender washer, the inner races of both the old bearings as spacers, and the nuts. Use 0.010” more preload
shims than came out of it. Tighten the nuts to around 40 ft-lb and measure the end play.

3) Take it back apart, and remove preload shims equal to the end play plus 0.002”.

4) Reassemble the distance tube, selected preload shims, and bearings, using the dummy shaft this time.

5) Divide the fork spacing shims that came out of it into two nearly equal groups. Insert one group of fork spacing

shims against each bearing, and put the seal tracks in.

6) Trial fit the hub carrier to the swingarm fork again. If it isn’t a snug fit, you need more shims. If the clearances

between the edges of the hub carrier and the inside surfaces of the swingarm fork aren’t nearly equal front and rear,
you need to redistribute the fork spacing shims.

7) Insert the skinny spacer ring C20180 in each end against the outer bearing race, along with an additional spacer

made by forming some steel wire about 0.060” thick into a ring.

8) Remove one of the seal tracks. Push the seal track into the center of an oil seal, and check it carefully to make sure

the lips are positioned properly on the track. Install the pair together, carefully tapping the seal in until it seats on
the spacer rings. Repeat for other end.

9) Install the hub carrier in the swingarm fork. Insert the fulcrum shaft, pushing the dummy shaft out the other side.

If the fulcrum shaft starts to hang up on a shim inside somewhere, merely turn the shaft to screw the shaft past the
shim.

10) Install washers, the link to the shock absorber bolt, and the nuts, and tighten.

REAR SWINGARM INNER PIVOT: Unlike the tapered roller bearings at the outer end that are sealed with felt, the
bearings at the inner end are non-tapered needle bearings and sealed with rubber rings with an X-shaped cross section.
These seals don’t really seem to be a problem. The rubber sealing rings can be replaced with an O-ring in a pinch, but
the OEM rings C17213 are probably better.

The bearings will still have the wear problems associated with non-rolling roller bearings. Gran Turismo Jaguar (now
defunct) offered brass bushings to replace these needle bearings; you could probably have bronze bushings fabbed up at
any machine shop. Since the OEM roller bearings are not tapered and have no adjustment, you should be able to easily
attain comparable or less slop with bushings as with the OEM bearings.

400

IRS UPGRADES: When searching the various sources for products to improve the XJ-S suspension, keep in mind that
the Jaguar rear suspension has been largely unchanged since the introduction of the E-Type. This assembly is very
popular with the hotrod and custom car types. As a result, ads for parts for improving this suspension can occasionally
be found in some decidedly non-Jaguar publications.

CHEAP REAR SUSPENSION UPGRADE: On the SportsPack, the bushings at both ends of the radius arms are
different. The bushings at the small end are made with a stiffer rubber. However, the bushings at the front end are the
same as on the standard XJ-S except that they are rotated 90º. These bushings have two holes through the rubber, and
on normal cars the holes are aligned with the radius arms so that push/pull forces apply directly at the holes. On the
SportsPack, the holes are aligned crossways to the radius arms, so push/pull forces apply to solid rubber. If you’d like
your IRS to be a little stiffer, you could apparently do some good with a press without even buying any new parts.

REAR ANTI-ROLL BAR BUSHINGS: If you are adding a 9/16” bar to the rear of a car with no rear bar or simply
wish to replace the existing bushings on a pre-1982 model, in place of the stock bushing C44931/2 and bracket C42114
you can use a generic 9/16” polyurethane bushing and bracket assembly available from many aftermarket sources. J. C.
Whitney (see page 691) offers “A” and “B” style “ProThane” bushing/bracket sets (see Dee Engineering, page 713),
with the “B” type being a little larger and more substantial. The “B” bushing must be modified slightly for the XJ-S by
cutting notches along the bottom edges, but polyurethane is easy to cut with a razor knife or hacksaw so it only takes a
minute and this makes an excellent installation. The “A” type would probably also work in this application.

If you are adding a heavier rear anti-roll bar or replacing the stock bushings on a Sportspack model, Addco (see page
710) also offers polyurethane bushing kits in sizes 5/8” and up and in several different styles. Their “B” series is their
“small shoulder style”; their “D” series is the larger, heavier unit with no shoulders; and they also have a “W” series
that is a large shoulder style. Any of these can be made to fit the XJ-S rear, although the “B” series requires that the
slotted holes be enlongated a little with a round file to fit over the studs. The “D” and “W” come only in urethane,
while the “B” normally comes with rubber bushings but can come fitted with urethane if you ask. The “W”, being
similar to the J. C. Whitney “B” type described above, may require the same minor trimming on the urethane bushing.
Addco’s catalog lists their “B” for the rear of the XJ-S, but the “D” or “W” are actually better choices.

As with the Addco front bushings, cutting a slit in the polyurethane rear bushing will make it much easier to install and
won’t hurt anything. At the rear, the loads are vertical but the bushings are mounted at an angle, so the cut should
ideally be made at an angle so it is located horizontally when installed.

ANTI-SWAY BAR END LINK BUSHINGS: If your XJ-S has an OEM rear anti-sway bar, the “dogbone” end links
(C42907) that connect it to the radius arms come complete with pressed-in bushings; when they are shot, Jaguar
expects you to purchase the entire dogbone. Joe Bialy found the individual bushings, though: “Try C10940. They're
$3.57 each from Welsh. I think they're an E-type part, but they are an absolute perfect press fit into the dogbone.”

If this is true, maybe somebody makes a urethane part for an E-type that could be used here. Or, maybe a larger
bushing intended for something else could be machined down for use here.

It isn’t all that important anyway; the OEM bushings are actually pretty stiff. The real problem is in the radius arm
bushings; see below.

GT Jaguar (now defunct) offered a rear anti-roll bar kit in which the end links appeared to be totally rigid, having metal
ball-and-socket joints at both ends. Note that, if a lack of harshness or noise is important, it may not be necessary to
have soft components at both the end links and the center mounts; rigid links at the ends may work fine for street use if
combined with rubber or poly center mounts. One would expect, though, that using rigid end links together with the
rigid blocks for center mounts might be best considered a competition-only configuration.

401

REAR ANTI-ROLL BAR MOUNT STIFFNESS: While you are trying to stiffen the mounts of the rear anti-roll bar to
increase its effectiveness, note that the end links on this bar don’t connect to the hub carriers. They connect to the
radius arms, which in turn are connected to the hub carriers via a very soft bushing. Hence, even if you make the anti-
roll bar mounts and end links totally rigid, much of its effect will still be absorbed in the soft bushings at the rear end of
the radius arms. Conversely, if you replace the soft bushings at the rear end of the radius arms with something more
rigid, you will suddenly find your rear anti-roll bar more effective. Note that the bushings at the rear end of the radius
arm on the SportsPack models are stiffer than the basic units.

REAR SUSPENSION REINFORCEMENT: Among those who have developed more torque at the rear wheels of a
Jaguar, the rear suspension cage mounts are a known weak spot. If your car can smoke the back tires, it apparently can
also rip these suspension mounts fairly readily. According to Mark McChesney, “There are hard rubber mounts
available from SNG Barratt” (see page 693). British Auto USA (page 689) also offers a set “in a bonded neoprene of
higher durometer than stock.”

However, the problem isn’t really with the stock mounts; it’s a result of the way in which the rear cage is supported --
which is in turn a result of the way the rear suspension works. Since the lower swingarms swing about a pivot parallel
to the centerline of the car, the hub carriers need to move only vertically and laterally through the suspension travel
range. The radius arms, however, pivot around their forward mounts and therefore try to pull the hub carrier axially
forward and back a little as the suspension travels. If all of the mounts and pivots were totally rigid, the whole
suspension would seize up. Since the cage is mounted at the top with four rubber mounts that are fairly close together,
the entire cage is free to tilt slightly forward and back to allow the radius arms to pull the hub carriers forward and back
a little. Also, the rubber mounts at both ends of the radius arms are very soft, so they can give a little to reduce the hub
carriers axial motion.

This all works very well under most conditions, but doesn’t take to drag racing well. The radius arms are supposed to
absorb the forward loading at the hub carriers, and also prevent excessive tilt of the cage assembly -- they attach to the
lower swingarms, but those in turn are rigidly pivoted (needle bearings) at the diff to only move up and down and not
forward or back, so cage rocking should be effectively limited. However, the radius arm mounts are soft and a lot of
torque apparently causes the entire cage to flex and twist, and the upper cage mounts seem to suffer.

The best solution appears to be to add some sort of additional link to accept the torque loads within the cage while
allowing the stock mounts to deal with weight loading only. Several of the aftermarket outfits reportedly offer some
sort of kit along these lines.

REAR SUSPENSION GEOMETRY CHANGE #1: The combination of rigid needle bearings and soft rubber mounts
in the rear suspension assembly have a net effect of pulling the rear wheels forward a little as the suspension travels
either direction from normal ride height; effectively, the hub carrier rotates about an axis that is roughly a line from the
inner end of the lower swingarms through the forward mounts of the radius arms -- an axis that is at a rather severe
angle to the centerline of the car. In other words, as the wheel moves away from level, it also moves forward and turns
in a little, providing a little rear-wheel steering. The effect of this stock design is to provide a lot of stability on the
freeway, making the car impervious to crosswinds and the like. (And you thought it was just because the car is heavy?
Get real.)

In racing, such stability due to rear wheel steering is also desirable, but to a much lesser extent -- a lot of it tends to
make the car corner poorly when fitted with racing tires and driven near the limits of adhesion. So, the radius arm is
often altered to move the forward pivot closer to the centerline of the car. The axis of suspension travel is still a line
from the inner end of the swingarms to the forward mounts of the radius arms, but since the forward mounts of the
radius arms are closer to the center of the car, this line is much closer to parallel with the centerline of the car. This
reduces the rear wheel steering effect and allows the driver more control over how the car drives at the limit of
adhesion. According to Mark McChesney, “Terry’s (page 693) is now selling a full kit to convert to a diagonal radius
link (with diff cage supports). I’m not sure the kit will work on an XJ-S, I think it’s intended for E-types.”

402

REAR SUSPENSION GEOMETRY CHANGE #2: The Jaguar IRS is commonly used on hot rods, Cobra replicas,
and other custom applications. In these applications, it is typical to mount the differential rigidly to the chassis of the
car and eliminate the radius arms altogether, in order to provide the cleanest and most visually attractive chassis. Some
people advocate making the same change to the stock Jaguar; the components are certainly strong enough to do this.
However, this is a radical geometry change from the stock IRS in the XJ-S resulting in no rear-steering stability
whatsoever and will make a quite noticeable change in the handling of the car. Also, having the diff rigidly mounted
will result in more gear noise and road noise transmitted into the car.

In both the hot rod and Cobra applications, the suspension is normally sprung so stiffly as to not move much anyway,
you’re driving a go-kart rather than a car, suspension geometry is not an issue. The Jaguar XJ-S is an excellent
handling car even though it is softly sprung. If you wish to maintain this, you should not consider eliminating the
radius arms.

Wheels and Tires

ALLOY WHEEL SEIZING: 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.

If your wheel is already stuck, you might as well try loosening all the lugs about two full turns, take the car down off
the jack and drive it up and down the street. Swerve left and right a couple of times. Of course, if the tire is flat you
won’t want to do this -- so you might want to check if your wheels are stuck now and take corrective measures before
you’re stuck on the side of the road with a flat tire.

XJR-S WHEELS: John Goodman reports that the XJR-S uses “8" wide special alloys (the front and back wheels are
not interchangeable because of different offsets).”

SPOKE WHEELS: Yes, a Jaguar with real wire 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 ‘50s
when Jaguars needed to maximize air flow to cool their brakes. Since that time, two changes have conspired against
spoke wheels:

1. 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!

2. 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 ‘50s. But it is a structurally poor design for modern
low, wide wheels.

Furthermore, Jaguar XJ wheels need an offset (distance from mounting surface to centerline of wheel) of around 1¼”,
which is not conducive to spoke wheel strength. It requires all the spokes to be crammed together near the outer edge
of the wheel rather than centered and optimally oriented for strength.

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 right is a challenge. Often the wheels must be returned to the manufacturer for truing. Truing will
obviously require removing the tire, remounting the tire afterward, and rebalancing -- so it probably would make sense
to plan on a wheel truing whenever new tires are fitted.