Ha Ha! Cheers,
Yes very observant it has only done 25,000 miles! It was originally a dark red metallic 2.4 that was stood on blocks for many years! It has now a fully rebuilt 3.8 in it with an all synchro S type box with overdrive. ( I still have the original engine If anyone would like to buy it ). It is very low geared as it has the original 2.4 diff which I would like to replace at some point with one from a 3.8 with lsd
Ray

 

You would be revving the heck out of your engine as the original 2.4 diff was a 4.29 and even with overdrive it is still a very low ratio.
I have a 2.4 MK2 which has been retrofitted with a late model all syncro OD box and a 3.77 diff and I have modified it with the Jaguar approved 1 3/4 inch HD 6 carbies. Goes very well!
The best diff for you would be a 3.77 which is correct for 3.4/3.8 MK2 with overdrive. I don't really think it is worthwhile chasing an LSD diff unless you have ideas of competition driving.
The simplest upgrade for you would be to source the diff centre/gears out of an automatic XJ6 (S1,2 or 3) which are typically 3.53. A 3.8 engine will handle the taller diff ratios easily ( unless you live on a cliff)
I think you would find that is the cheapest and easiest way to up grade your very nicely finished MK2.
Cheers
Bill Mac
MK1
MK2
XJ6S3
X300

 

Hi Bill,
Thank you that is very useful information, I will be looking out for an XJ6 diff now!
Cheers,
Ray

 

Spot on. 3.77 : 1 is ideal for the MOD all Sync box with longer 1st gear than the Moss. Perfect from in town to high speed cruising. For general use LSD is only of real help if you drive hard in the wet often or on dirt. My S has an LSD 3.77 & I doubt I've ever triggered it hard.

 

I've taken a look at the XJ6 Diffs and I didn't realize they had independent rear suspension, so what you are saying is that it is possible to remove the guts and put it into my back axle?

 

Rear diff set up on the XJ6 is the same as the 60s S type, E type, Mk10, 420 they just had different length drive shafts and some had bigger brakes. The diff sits in a cage that is bolted to the underside of the car where as the Mk2 is a solid back axle. The diff externally is not the same as the Mk2 although the internals ie crown wheel and pinion might be the same. You would have to compare part numbers.

 

The differential centres are interchangeable.
Don't worry about the housing, Whether hard (live)axle or independent.
Heaps of XJ rear ends around unless the hot rod builders have got there first. Very common in OZ hot rods as the whole rear suspension cage assembly bolts up easily to a hot rod body.
cheers
Bill Mac
MK1
MK2
XJ6S3
X300

 

A 4.29 axle might be good for racing on a short, tight circuit, but not for general touring. Some of the later (not sure how late) XJ/XJS diffs are Dana rather than Salisbury and may be more difficult to swap into a live axle. As I understand it (I've not tried) swapping the internals of a Salisbury diff is not minor work. If you can find one in good order, the easiest way to a better ratio is a live axle from any 3.4 or 3.8 Mk2. The autos and non-ODs are 3.54 and the overdrives are 3.77. The 3.8 axles are LSD, which might or might not be an advantage - I'd take it for use on snow or mud or for racing but nothing else. The 3.4 and 3.8 axles are more difficult to find and significantly more expensive than the lower ratios from the smaller engined cars. My guess is that, while 3.77 is quite acceptable, the best ratio for most people's uses of a 3.4 or 3.8 Mk2 would be 3.54 or even 3.33.

A final note, when removing a Mk2 axle, remember it's very heavy and will break anything it falls on. Do not put your fingers between the axle and the flange on the fuel tank.

 

I have found a complete set up from an S type with a 3.54 ratio diff in it! Could I leave my axle in place withdraw the halve shafts and swop the diff that way? I've looked in the Service manual and it doesn't look straight forward. The guy is going to check the Diff flange for movement on Monday they are asking £500 for it
Cheers
Ray

 

Peter. Do your axle ratio comments hold true for Moss and synch4 gearbox?

The scribes comment:

"The Moss gearbox was, frankly, old-fashioned and was not at all suitable for a car of the S-type’s pretensions, let alone those of the Mk X in which it was also available. Perhaps customers who bought the S-type as a small luxury saloon usually chose the automatic option, but there was no doubting the need for that new gearbox."

"Despite these advances, the Jaguar [synch 4] gearbox still has its detractors more than fifty years after its introduction. They argue that the higher first gear takes the edge off initial acceleration; that the gear-lever travel is longer than on the Moss gearbox and so hinders quick changes; and that the newer gearbox lacks the character of the older one. So be it: Jaguar probably knew at the time that they would never be able to satisfy everybody when they introduced major new components."

All those magazines that road tested the synch 4 equipped car don't agree.

By character I presume they mean the loud whine from the straight cut first gear in the Moss?

 

Yes ~ make sure that the pinion bearings have not lost preload.

We did a complete rebuild of my 3.77 and it's quite a job setting up the crown wheel & pinion meshing correctly & setting up pinion bearing preload. The reward, however, is a dead silent axle.

Long section H of S Type Service Manual.

 

To me the price sounds fair for good secondhand and cheaper than a 3.54 live axle. When you say 'in place' do you mean on the car? I think that it would be far better to have the axle on a bench. As for the difficulty of the whole swap process, I don't know as I've not done it. I know someone who swapped the Salisbury diff in a Land Rover and it took him several days as nothing wanted to come apart. Of course, Land Rover axles aren't exactly the same as Jaguar and most likely have had much harder lives.

 

The 4.2 litre series 3 XJ6 comfortably pulled a 3.33 differential. The 4.2 litre engine obviously has more torque than a 3.4 or 3.8 Mk2, but the car is also significantly heavier. As for acceleration off the line, is that something that we care too much about with our old cars or Jaguars in general? The whine (or scream) from a Moss box in first makes most, certainly me, change up fairly soon after the car starts moving. As a ratio, it seems to have been chosen for pulling out tree stumps or climbing vertical slopes. Still, the 3.4 with 3.77 final drive will drive off in its relatively tall (Moss) second gear on level ground, so 3.33 in bottom shouldn't be impossible. Acceleration through the gears should not suffer too much, just hold the lower gear a bit longer. The advantage is saving a few hundred rev/min in motorway cruising.

Going back to the series 3 XJ, the 3.4 litre version had a 3.54 axle and about the same bottom gear times axle ratio as a Mk2 with OD. Accounting for the weight difference, I think that makes a 3.33 OK for our cars, certainly 3.54 should be fine.

I'm no great lover of the Moss box, but if I am to swap it, I really want something a lot better (Ford 6R80, ZF 6HP ...) to make it worth the effort.

 

It looks like its a major job, I've made a hub puller which I used to replace the discs but its saying you need a tool to spread the axle casing ??. I could buy an empty axle casing as there are a few of those for sale and build it up ready and just swop it, or bite the bullet and pay nearly a grand for an unknown 3.8 complete assembly for sale on eBay. I'm in no rush as its drivable although its very low geared I don't suppose I'm going to find one that's only done 25,000miles like the one that's in it. I swopped the diff in my MGB in less than an hour!
Cheers
Ray

 

To Peter ~ Thanks. I actually enjoy the intermediate ratio selection on my S ~ well chosen. First is just fine for how I drive. I don't find it too long at all.

Did they change GB ratios for the XJ6's? I know they changed the tooth cut to make them a little quieter in the intermediate gears.

 

I'd be inclined to have a go, especially if you're confident that it's a good diff. May be it will go easily like your MG. If it doesn't, your only loss is some time. And considering the amount of time we invest in our cars, a bit more hardly matters ...