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XJ-S Final Drive

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Rear Suspension/Differential Removal

It is discussed in the section covering Steering & Suspension.

Differential

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) ratios.

DANA

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.

Replacement Parts

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 sturdy.

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 Nut

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.

Differential Output Bearing Failure

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 check everything.

 

On to the Brakes

 

 

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