David C. Hobson, DDS

The differentials on our beloved older Jaguars are normally quite reliable. (Unlike some other parts - dare I mention vintage Lucas electrical components?!) Trouble free mileages of 150,000 miles and up are not unusual. However, when problems DO arise, it can be a bit intimidating even for professionals. Thanks to a mechanic who did a beautiful job of cleaning and detailing the rear end in my XK14O OTS, but who forgot to refill it with 90 weight gear oil, I gained quite an education in the rebuilding of vintage Jaguar rear ends! This article is submitted in hopes that it will simplify the process for other owners faced with similar problems. Oh, and for those of you who have wondered what happens when a rear end is run without oil, it starts with strange howling noises, and ends a few miles later when the pinion shaft and bearings overheat and seize! NOT a pleasant experience! By the time it seizes, gear faces and surrounding bearings are beyond hope.

This article is not intended to be exhaustive for all Jaguar rear ends. I have no information on the ENV rear axles fitted to early XKI 20s, nor on those of pre-war cars. It appears, though, that all Salisbury units fitted to later XK12Os through 150s, plus the IRS units on at least some E - Types and XJ 6 saloons used the Dana Spicer 44 gear sets. Though the XJ 40's didn't use Spicer 44 units, I'm told that they can be adapted with only minor modifications. Spicer 44 gear sets are clearly marked with the manufacturer's name and ratio, and must be replaced in matched sets. (There is an ID number on both ring and pinion gears which must match.)

BEARINGS: The bearings used on Jaguar rear ends are the same part numbers as those used on American applications, including pinion, carrier, and wheel bearings. These are readily available through driveline shops or bearing supply houses. The only thing unique to the Salisbury axle are the shims under the brake backing plates. They're not readily available, but can be made using shim stock if necessary.

USED GEARS: Spicer 44 gear sets were used on Ford trucks, AMC vehicles, Jeeps, and most older front axle units of US made 4 wheel drives. (They may be common to other US vehicles as well.) They are also found on Sunbeam Tigers, 283 and 427 Cobras, and probably many other larger British vehicles. Spicer 44 is even available in a limited slip version for those of you inclined to go racing. As for replacement parts, there are many used gear sets sitting in wrecking yards. The front axle of a 4 wheel drive vehicle which has had little off road use may be in near new condition. The difficult thing about obtaining a good used gear set is finding it! They come in numerous ratios and varying conditions. If still attached, the manufacturer's tag fitted to one of the cover bolts may provide information on gear ratio. But to assess condition, at least the differential cover must be removed to visually check things out! This can mean a significant investment of time crawling around a wrecking yard, with the yard owner concerned about possible dirt and water contamination once the unit is opened.

NEW GEARS: On new gear sets, there's also good news and bad news. The good news is that brand new Dana Spicer 44 gear sets are readily available off the shelf at larger driveline shops. Cost is around $350 - $400, and they are available in all catalogued Jaguar ratios, as well as several others not originally fitted by Jaguar. If you decide to change ratios, remember that the speedometer must also be modified. Unlike new vehicles, which have electronic speedometers and require only some computer reprogramming to accommodate a new axle ratio, the old mechanical ones are a lot more complex when rear end ratios are changed. (The Jaguar factory parts manual lists a different speedometer head part number for each rear axle ratio, though a knowledgeable instrument shop may be able to offer alternatives.) The other bad news is that in the mid 1960's, Spicer changed from a coarse, 10 spline pinion input shaft to a fine, 26 spline shaft. And new gearsets with the old 10 spline input shaft have not been available for some years now!

The first proposal given me was to change the end of my driveshaft to accept a universal joint yoke, as my old pinion shaft companion flange would not fit the pinion shaft of a new gear set. (Americans typically put the universal joint yoke directly on the pinion shaft, unlike European and Japanese builders, who use a companion flange between the pinion and driveshaft universal joint.) This involved a lot of extra work, and would have ruined the originality. I looked in vain for a good used gear set, but came up with only one old one which had been damaged by water to a greater extent than I was willing to accept.

I checked with several well-known vintage Jaguar parts houses, but no one could suggest a solution. The logical fix would have been a new, 26 spline companion flange, but I was assured that none was available. I began exploring having a new one welded up and machined, and began looking for someone who could do the fabrication. However, in making one last check with a Jaguar-only wrecking yard located in Central California, I was delighted to find that not only was the proper flange available, but that they had a new one sitting on the shelf! I've since checked the part number, and found that Spicer still supplies it by special order. With the new flange, it's possible to adapt the new gear sets to the older cars without having to modify the driveshaft in any way. Personally, I felt that new gears were well worth the $200 or so difference over a used gear set.

The Dana Spicer part number for the new 26 spline companion flange, which replaces the old 10 spline flange perfectly, is:

DANA Spicer 2 - 1 - 2391


Given the limited amount most vintage Jaguar owners drive their cars, a complete rear end rebuild using new gears and bearings will probably outlast both the owner and the car!

One other item which may be of interest to all the membership, whether or not their differentials need major work: The original Jaguar fill and drain plugs use a square head which is easily rounded off with a wrench (spanner.) New plugs are available from driveline shops, which have a receptacle, which accepts a inch drive ratchet head or breaker bar, thus preventing any possible slippage or rounding off. They even come with an internal magnet, which picks up any bits of metal, which might get loose in the rear axle housing. Great insurance for only a couple of dollars each!

This article may provide a starting point for other owners or specialists to contribute their knowledge on pre-war rear axles, as well as later information on Jaguar rear ends from the later '60s to the present. My experience talking with parts suppliers dealing with older Jaguars is that they don't sell a lot of parts for rear axles, and as a result, aren't really that knowledgeable as to problems and solutions when major work is required!

My thanks to Kevin and his staff at Six States Driveline Service in Orem, Utah, for their patience and help in getting my rear end rebuilt! I'll be happy to answer other questions as to parts sources, etc., if anyone would like to write or send an e-mail.

David C. Hobson, DDS

3882 N. Little Rock Dr.

Provo, UT 84604