Oh yes! The parts are heavy and awkward too, I thought I was lucky to get through the process without getting a finger pinched. Always "fun" to get the preload shims correct and the backlash at the same time.

 

Hi, this is Andrew from Jaguar Specialties and I noticed this thread on the differential change. One question that came to my mind was this- are you planning (eventually) to go to an overdrive transmission in this car??? I think you may need it with a 3.54.

Using a basic rpm calculator, and assuming a stock tire size (215-70-15; 26.9" tall) the car will be pulling nearly 3200 rpm at 70 mph. Will that be acceptable long term, or on a long trip?? It seems pretty high, even for a smooth V12. And that is saying nothing for what will happen to fuel mileage.


Just my $.02

Andrew
Jaguar Specialties

 

You are absolutely right Andrew.

I put 3.58 gears in mine it was great when I lived in Sydney as the car hardly ever saw 100km/h, now I live rural it's another matter, with 3000rpm @ 100km/h, not a relaxed cruiser. My car now has a 4L60e and turns about 2100rpm at 100km/h, much better

 

I've been debating this for some time now. The 3.5 gears would be great. I think I'll swap the tranny to the 700R4 with 2500 stall converter first. It has a lower first gear. Then swap the diff for the 3.5s. I have a sbc and comfort is not what I built this car for.

 

Agree with Andrew and Warren,
My 6.0 has 3.54 diff as standard with GM 4L80E (4 speed plus torque converter lock up), tyres are 225/50 x 16, if memory serves me right 3000rpm is 90mph and will cruise all day long at this and much higher speeds, speed limits and fuel stops excepted.

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.

yes my RHD Euro/spec XJS 1978 had 3.07 ratio powerlok, now has 3.73, with 700R4 OD!

lot of low speed acceleration and good hiway cruise, with 2.60 final ratio!

 

what I'm looking for is the actual part numbers of gears and bearings and seals and spacers etc to make the gear set work. I was offered a 3.54 rear end for what I think was fair, but I also think changing the gears and "rebuilding" it at the same time would be less than what a complete 3.54 diff of worth. A gear set is about $175. I haven't seen a "rebuild kit" for the differential or what exactly Dana 44 gears will work and if any special parts are needed to use them? What is the most gear I can run with the stock posi unit (carrier). I assume it's a posi , stock for USA 1988 V12?

 

If your current car is 2.88 ( as I suspect it is), that's the lowest gear you can run on that carrier. 2.88 was the break point, so 3.07 and numerically larger gears need a different carrier.

If you look here you will be able to get the part numbers of the components you require. Bearings are the same across all the ratios. The SNG Barratt website is also good for finding part numbers.
https://www.jaguarclassicparts.com/u...nit-components

The Dana 44 gears an be used, you'll need sleeves for the ring gear bolts, as Dana uses 3/8" bolts and Jaguar uses 7/16". The pinions are different too, you won't be able to use the splined Jaguar flange and driveshaft connection. It's been done, but it's not exactly drop in replacement for the Jaguar gears.

 

As an alternative to the Jaguar pinion seal you can also use Land Rover part AAU 3381.

 

http://www.m.ebay.com/itm/JAGUAR-XJ6-X300-XJ40-XJS-4-09-CROWN-WHEEL-PINION-DIFFERENTIAL-GKN-DIFF-AXLE-/222456591970?nav=WATCHING_ACTIVE

 

That's for an XJ40/X300, it has the longer pinion to act as a locating pin that goes into the driveshaft. The extension would have to be machined off at the threads to use the flange on an XJS driveshaft.

 

Yep, that's exactly what I did, and used the original XJS nut.

 

I thought it was the opposite. 3:31 was in the early US cars 71-74 and then they went to 3:07 Before switching to 2:88. In 1981
To be fair I never raced with anything other than a 3:54 switching tire diameters depending on which race track I was at.
Never did race with a speedometer.