I am going to attempt to document as best l can what the weekend changeover from 14HU open diff to 15HU LSD entailed. Ratio was also changed from 3.06 to 3.27.

Donor diff was from 1996 XJR. I stripped this out but bearings were good so cleaned all out and replaced clutch packs.
These later diffs are still being labelled as Powr Loks but they differ from the original powr lok in so far as they lack the ramped cross pin. Clutch packs were replaced with the original spicer powr lok set along with a shim to give me a breakaway torque of about 80lb ft.

Rear end out and diff removal was pretty straight forward as was the reinstall.

Besides the obvious offset pinion and flange type, there are some other differences ( at least on mine) between diffs which are easily fixed but do need to be aware of. The lower rear mount pins on 14HU are much shorter in thread and if used in the 15HU there will only be about 10mm thread engagement into the diff body. The pins on my 15HU protruded more and were larger diameter but were easily turned down to the 17mm required and a simple spacer turned up to account for extra length.
The top brace mount on the 14HU is thicker than the 15HU but shorter bolts is all that is required there.

The pinion spline of the 15HU is 10 spline count so an earlier flange needs to be used in place of the jurid flange, and of course the nose of the pinion needs to be cut off. These flanges are different depths and the nut will now protrude but since a 20mm spacer is needed anyway it is not a problem. The spacers are readily available and generally sold for land rover lift applications.
The locating ring height on the XKR flange/uni joint is 4mm compared to only 2mm normally so matching recess of spacer will likely need a little turning.

Exhaust hangers are slightly different on each of the front diff support panels but a simple angle bracket is all that would be required to move it the 40mm or so it needs to move. My system is under axle so it was not an issue. I did record the relative positions and will knock up a bracket.

Ratio change was the stumbling block on the XKR because of TCM non programmable issues but huge thanks to member "Chirpy" that seems to have been solved by spoofing the CAN coms.

Test drive with new diff/ratio showed no issues, performance best descibed as normal mode now = sports mode old. LSD performance will take more testing to get the feel of difference.

Long post but l hope it may help anyone considering the same change.

14Hu open original

15HU LSD

Spacers made to account for longer lower pins

15HU pin on right turned down to 17mm.

Original pins. 14HU on left 15 on right.

Plenty of tunnel clearance after moving 25mm needed for offset pinion.

Because of flange depth difference a 20mm spacer is required.

The "Chirpy" module needed to satisfy the brains of the vehicle.

 

TCM EGS51 can be reprogrammed for new gear ratio but it costs $$$ .

 

it appears some of them were reprogrammed but the source of that service seems to be very difficult to find for some time. Also with the costs quoted some years back of several thousand dollars, spoofing of the CAN messages would seem to be cheaper by at least 10x.

 

Yes, it's good that there is cheaper way to do it. I have one of those TCUs reprogrammed for 3.58 . I think it was the last one done and it was already five years ago.

 

Baxtor,

Now that you've done all this and spent the Money, could you please give me some performance figures indicating the advantage of doing all this work and spending all this money? Like how much did it cost overall........and what was the overall advantage in seconds or in power output? Would you do it again?

Billy Clyde @ Cinco Ranch

 

Billy Clyde, where have you been lately? Some of us were wondering if Covid-19 got ahold of you....

 

l can't give you times Billy but first test drive after change had me grinning like a kid. It sure feels much faster on pick up and that's what matters.
The original aim was not the ratio change it was the stronger diff and LSD, the fact that diff came with 3.27 gears was going to involve more work changing those out to something closer to the 3.06 to satisfy the TCM.
The CAN TCM workaround came from Chirpy just about the right time so l decided to leave the ratio and give it a go.
The XJR diff cost me 650 AUD, new clutch pack plate kit 120, oil 25, and CAN module 140. Not a whole lot of money and a weekends work. Would l do it again?... in a heartbeat.

 

This makes me want to do it as well, but the ZF 6HP26 TCM is quite a bit harder to get to. I definitely needed it yesterday. After I left the gym, I still had an adrenaline rush did some very spirited driving around canyon roads with tight corners, and managed to get the tail to step out a few times with the traction control off. I then managed it on the city on the roundabouts as well. An LSD would make sliding the car much more predictable.

 

Certainly no expert on CAN stuff but even with the TCM hidden away inside the trans, any external speed related message to it still needs to travel along those green and yellow wires. Is there any reason they cannot be interrupted somewhere suitable in that harness? I don't know but somebody will.
LSD only could probably be done with a centre for your existing diff. If ratio change couldn't be accomadated l was going to swap out the centre carrier in the 15HU for 3.07 gears from 1976 xjs. I believe that would have been close enough to satisfy TCM.

 

Sorry to drag up this older thread, I am following baxter's path and putting a 15HU with an LSD in my 2000 XKR as a cheaper and stronger alternative to the Quaife in the 14HU. I am even going to try my hand at building and programming the Chirpy TCM module! My question is where did you (baxter) find the parts to replace the clutch packs in the LSD? I can find carrier bearings locally if needed and don't plan to touch the pinion other than replace the leaking seal but cannot find clutch discs or specs anywhere? Any info you can share?? Most of the local transmission shops wont return my calls when I say Jaguar. I should start telling them I have a Dana 44 and see what they say!

 

Clutch pack kit l used is shown, l did play around with shimming to get the preload l was after. As usual my record keeping was not up to scratch and the memory is no help as to exactly what l did.
The XJR diff l used, although still called a power loc differs from the earlier split spider gear type and l felt a little more clutch pack preload would help.

 

If anyone is looking for the Chirpy TCM wheel speed spoofing solution, it's here:-

https://github.com/chirpy8/canbus_x1...xleRatioChange

 

Thanks for the link. I was just getting ready to question if it was an Arduino solution. Not that I am going in this direction, but my Arduino knowledge is very limited to my 3 virtual walls for my robot vacuum. Curious minds just want to know.

 

Hello forum,
I'm not a Jag person...... but with a garage of AC bits and pieces and missing 2 differentials.
They should be Salisbury 4HU 'bolt-nose' type - basically like the E-type / XJ 4HU but with the 4 bolt casting holes as on the 14HU and 15HU type used on later Jags.
I've two options (without paying a fortune for a newly made copy of the AC 4HU, or lucking into finding an original one):
a) take an E-type / XJ one (I need Powr-Lok LSD type and probably one with approx 3.3 and another with approx 3.5 ratios) and get nose and side brackets made to make it fit the AC chassis mounts without mods to the chassis.
b) take a 14HU or 15HU - while not the same spec at all - the mountings probably would work better, though not look as original.
My problem is that while second hand E-type / XJ 4HU diffs are mostly clearly marked with tags on a rear cover mounting bolt - saying 2.88, 3,31 etc for ratio and PL or BPL (by the way what is the difference between PL and BPL?) but the 14HU and 15HU diffs seem not to have any markings or tags indicating what ratios they are nor whether they are Powr-Lok Limited Slip diffs or not.
There are loads for sale of both - but there seems to be a lack of knowledge with the sellers of 14HU and 15HU diffs - they seem simply not to have a clue what they are selling. All seem to quote UK registration plate numbers as though it were possible to access DVLA (UK car registrations) and get to what the car was and a the spec that would tell me if it was a diff that I might consider. Firstly those records are not available, secondly most of the cars have been dismantled, scrapped and records deleted.
So is there anyone who on the forum who could give me the basics of which 14HU and 15HU jag diffs were Open and which were Powr-Lok LSD type?
And any way to easily identify the differences?
And how to know the ratios?
I'm assuming no-one has an E-type / XJ with diff with bolt-nose mountings also?
Any help would be really appreciated.
Thanks - James

 

14 HU has central pinion and 15 HU has an offset pinion. LSD is marked with an orange cross on diff cover but generally speaking any 14HU you find will be open. My LSD 15HU came from XJR, l believe most other models were open.
l will also note that although the LSD are still called power lok, the design was changed slightly and no longer incorporated the cross pin ramp design, instead just relying on the bevel gear for clutch pack lock up.
For improved performance l would consider transplanting the internals from an earlier true power lok into the 15 HU case, this cannot be done for the 14 HU.
Ratio ID is either a matter of tags or actually turning and counting revs.

LSD label on 15 HU

 

My understanding of the 15HU labels:

Black cross - Power Lock (I think BPL = British? Power Lock, PL = Power Lock)
No black cross - Open diff

Orange: 3.27
Yellow and Red Stripes: 3.58
Brown: 3.77
Blue: 4.09
Green: 2.88

So Baxtor's photo of the square label shows a 3.27 Power Lock.

and the weaker HU14 are nearly all 3.07 except for a few 3.27s in selected markets/models, all open diffs unless upgraded aftermarket.

 

Many thanks for that useful info. That's a big help as I'm trying to avoid a rebuild. So it looks like the 4HU type with brackets front and side will do the best job for my AC428 rebuild. Very useful to understand the 14HU and 15HU differences and that Powr-Lok info on the 15HU helps knowing that in advance.

 

sorry to revive an old thread. I have a lsd diff from a 94 xj6 can anyone help and inform me what pinion yoke I need to eliminate the 3 bolt jurid yoke ? Thank you in advance

 

I used a stock XJS pinion flange, need to cut off the jurid nose from pinion. As far as l am aware all the pinion spline counts are the same.