[E-Type] Diffs

Hi all .
Can the xj12 /xjs Diff be transplanted directly into a S1 4.2 They are
both Specified as Salisbury 4HU . and LSD .Looking at drawings in the
Manuals the only difference appears to be that the Half shaft stubs have a
detachable flange on the outboard end in the older version.
I an looking to fit a higher ratio as mine has a 3.5 and I am always looking
for another gear,also I have a good chance to pick up a 12 diff.

Hi Colin,
You are indeed correct in that the diffs are exactly the same case with
different ratios. The output shafts and their associated bearings are
different but as far as the swap is concerned it makes no difference
whatsoever. The XJ12 also had a choice of ratios and they ranged from 2.88
to 3.54, depending on specification and market. You can check the ratio by
looking at the small alloy tag fitted to the differential cover. These tags
often get broken off or are missing. The only way to check the ration, if
this is the case, is to remove the diff cover and then you will find the
ratio stamped on the outside edge of the crown wheel. The figures used
express the number of teeth on the crown wheel and the pinion, such as 43/13.
Hope it helps.
John J. Black

I advised you off list hope it was of help ?

One thing you must be careful of is the fact that the Diff of the XJ sits at
a different angle that is the geometry is different.

This is done by the side members "Mount Bracket"s that bolt to the actual
Diff Head,“CENTRE” they carry the Fulcrum Shafts,the angle is different so
use your
E Type ones on the XJ12 Diff Centre.
You can mix and match the Jag “Mount Brackets”, move the Holes in the Cradle
to get different handling, problem is go the wrong way and it will not be a
user friendly car, it will bite.

If you misplace or lose the original side members,you too will be lost.
Often people exchange the Diff and leave their E Type Side members on.

I think a 2.88-1 Diff is an over kill on a XK engined E Type, first gear
becomes too high
if you need to do hill starts it rip’s the clutch too much.
The 3.07-1 is the highest I would recommend for a XK Engined manual
Transmission “E” Type, even that is too high for me,I like to stand a chance
against the Hyundai’s off the lights, Gees! I hate Hyundai’s.
“Rocket Dan” may need a 2.88-1,do we need one of those Dan ? I would be
thinking 2.56-1.
Terry @JAGPRO__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com

Hi John. Seems to me in the S-III there are some external differences such
as caliper mounting flanges-some have 5 holes and some have ?7 holes. Can
either caliper be used?? Thanks and


Rex Henderson
72 2+2

This is the kind of stuff that makes this list really valuable…
LLoyd - well, I’ld have never guessed… -

JAGPRO wrote:> Colin,

One thing you must be careful of is the fact that the Diff of the XJ sits at
a different angle that is the geometry is different.

Hi! Listers,
Further to the Diff Thread, if when fitting the later or alternative Diff
Centre “Head”
Go with the Caliper Brackets that come with that Centre.

Sometimes there is a slight difference where the Callipers mount,that is the
length of the bolts, so get the calliper bolt for the centre you are
purchasing,best get the whole thing calipers and all, then your not running
around in circles trying to locate or figure out differences.

The best caliper to fit to the rear is the series 3 XJ6,reason the Pistons,
Dust Seals are superior to earlier models,also the pistons are cheaper at
least in Australia they are,the calipers require the suited bolts and a
little has to be ground off one mounting lug.

Generally speaking the Ser3 XJ6 Diff is in better order then earlier Diffs.
Most ser 3 are not LSD, most E Types do not really need LSD as they are not
driven hard enough to take advantage of the power and or they are not
generally driven in extreme weather conditions.
If I’m driving around in an E Type with 3.07-1 Diff and four speed, I don’t
really have enough Grunt for it to be a problem that I lose traction and end
up in a precarious situation.

Terry @JAGPRO__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com

C & D Clayton wrote:

Can the xj12 /xjs Diff be transplanted directly into a S1 4.2


I did this swap earlier this year. I put a 3:31 from an XJ-S of
indeterminate vintage into my 66 FHC. The job went smoothly but there are
a couple of ‘adjustments’ to be made.

  1. As Terry Handley mentioned, retain the lower fulcrum mounting brackets
    from your car to use with the new diff. When you have the pieces apart in
    front of you the differences between them will be obvious.

  2. You will probably have to change over to the newer style calipers as I
    did. The diff housing had been changed and would not accommodate the S1
    calipers. To me that was a bonus.

  3. Related to 2, the calipers “just” clear the cage, and I don’t think the
    pad retaining pins can be removed while the calipers are in situ. I didn’t
    see any appreciable pad wear in the previous 20 years I’ve owned the car so
    I’ll probably never have to worry about it. In 40 or 50 years someone will
    be referring to me as a “DPO” when they’re trying to replace the brake pads.

  4. Also related to 2, the emergency brake linkage has to be altered ever
    so slightly for the new calipers, but nothing more than the substitution of
    a bolt for a clevis pin.

As for ratios, I couldn’t be happier with the 3:31 compared to the ‘mph
challenged’ 3:54. I originally wanted to go with the 3:07, but I don’t
think it would be a good choice unless all you did was highway driving.
The 3:31 seems to be perfectly suited for the car.

Good luck with the swap if you go ahead with it. Feel free to contact me
off-list if you need any other gory details of my experience.

Jack Terrick
66 FHC

–Thanks folks for the info received re the conversion to higher ratio/later
diffs ,it helps to hear from those who have been there and done that first
hand.I will now set my stall out for a future slot.
Colin C.