It is discussed in the section covering
The XJ-S has apparently been fitted with at least three different
differentials ("final drive units" for you Brits).
Salisbury 4HU Powr-Lok
From 1976-1985, the differential was a Salisbury 4HU Powr-Lok that
came with either 3.07:1, 3.31:1 (1976-1982), or 2.88:1 (1982-1985)
From 1985-1987, a 2.88:1 DANA unit was used. This unit can be
distinguished in that the bearings on the output shafts are held in
place with three bolts; the differentials both before and after these
years have five bolts. It also has no drain plug.
When working on a DANA unit, you can get the seals from Jaguar,
bearings from a local bearing house, and the clutches, shims, and
those silly little clutch retainers from any performance shop that
has access to Dana rear end parts. When ordering, they will usually
ask for a ring gear diameter and an "axle" spline count.
Clutch Retainer Problems
Jaguar does not want to admit to the Dana as having ever existed.
The problem is those "silly little clutch retainers." The Jaguar,
with it's high weight and sticky tires, really hammers on the
clutches, which eventually chew through the retainer. By design, the
half retainer can't get out into the gears where they would do major
damage. But it does get pushed out the end of its access hole,
mucking up the carrier bearings.
GKN Power Lock
Beginning in 1987, there was a differential referred to as the GKN
Power Lock with a 2.88:1 ratio.
Jaguar Diff Repair Procedure
Reportedly, the official Jaguar repair procedure for final drive
units is to replace them as a whole.
Limited Slip Diffs
All XJ-S differentials are limited slip, and all the systems
operate using essentially the same principle (a series of friction
discs, with the compressive load increasing through increased drive
torque) although the feature has often been given different names.
DANA LSD Replacement
The gears for the DANA Type 44 limited slip differential will fit
in the Jaguar unit. This includes gears from many larger American
cars and small trucks. However, there are problems that must be
overcome. First, the DANA ring gear will be threaded for smaller
bolts than the Jaguar originals, so bushings will have to be
fabricated to make the smaller bolts fit snugly in the holes.
Second, the replacement pinion will not mate with the Jaguar input
flange, so a Chevy input yoke will have to be used. The Chevy yoke is
the type with U-bolts that retain the U-joint bearing caps directly,
so the flange on the rear end of the drive shaft will need to be
removed. Since the Jaguar driveshaft uses standard Chevy U-joints,
they will match up fine.
The salesman at Quality
Jaguar reports that while the DANA gears will work, they are
considered inferior to the Jaguar parts. Specifically, they tend to
whine more, and of course the smaller mounting bolts are not as
Differential Oil Change
Getting the fill plug out is no picnic. It has been suggested that
removing the center reinforcing plate under the final drive unit (14
bolts, 6 with nuts) may be worthwhile. Don't worry, the whole car
won't fall apart while the plate is out.
Many Jag owners suggest a length of plastic hose and a squeeze
bottle for topping up or filling up the final drive unit. The hose
should be long enough to feed out the right side wheel well so the
oil can flow downhill.
Fill Plug Access in Boot
Brian Sherwood points out that if you open the boot, remove the
spare tire, and peel back the matting forward of the fuel pump, there
is a round metal plug; removal of this plug provides access to the
fill plug on the differential.
I just popped it out with a screwdriver, did my lube thing,
then pressed the plug back in with some RTV around the edge.
LSD Gear Oil Additive
Note that while the diff can be topped up with conventional gear
oil, a drain and refill requires an additive for limited-slip units.
According to a salesman at
Quality Jaguar, the XJ-S
final drive unit uses both natural leather and natural rubber seals.
Therefore, synthetic lubricants are NOT
recommended. It is recommended that synthetics be avoided in the
special additive as well.
Input Flange Retaining
It's a really big nut, obviously it should be tightened down
really tight, right? Wrong. This nut is used to set the preload on
the input shaft bearings. Between the bearings is a "crush sleeve"
and during assembly this nut is tightened just enough to provide the
proper bearing preload while compressing this sleeve. If the nut is
overtorqued, the entire final drive assembly must be torn down to
install a new crush sleeve.
One of the common failure modes of the Jaguar differential unit is
the failure of the bearings in the output shafts, possibly because
these bearings take lateral loads imposed by the working of the
suspension. Whatever, the failure is usually indicated by clunks from
the rear when driving or the tire rubbing the wheel well where it
formerly had clearance.
Checking by grabbing the top of each rear wheel and shaking
vigorously in and out clearly indicates a problem. Closer inspection
shows that the output shaft is free to move in and out, and the only
thing limiting movement is the brake disk banging back and forth
within the caliper!
According to Jan Wikström,
It's very likely that all you need to do is replace the
bearings and seals. This is not difficult, but you'll need to take
the rear subframe off your car. You can do it from underneath, but
that probably takes longer because of the difficulty in getting the
brake calipers off and back on. Besides, taking out and dismantling
the complete rear suspension gives you a great opportunity to
On to the Brakes