Hello all,

I am thinking of potentially buying a 98-03 XJR as a fun summer car and in doing some research was surprised to learn that these cars were never offered with limited slip. I am interested in installing a true mechanical limited slip, as the electronic strategy of braking one wheel under slip won't do it for me.

So, some questions...

• Did the 98-03 XJR only come with a 3.08 open diff?
• Are the earlier XJ40/X300 differentials compatible with the X308?
• If so, what years/models of XJ40/X300 came with an LSD and what ratios were available?
• I read about the offset pinion flange on the earlier cars which is different from the centrally located pinion flange. What assemblies are required from an earlier car to support the conversion? I would think at a minimum the differential, subframe/cage, and driveshaft?
  • Jaguar Specialties
• If I install a diff with a numerically higher ratio, is any tuning required so that the ECU/auto trans isn't confused? Or is the speed reading taken from the rear wheel speed sensors?

There is a '95 XJR (supercharged 6 cylinder) in a salvage yard by me that I may use as a donor.

Thanks in advance!

 

what is your intended usage of the car? For day to day driving I don't think the lsd is really necessary and even in harder driving, its probably not worth the time, money, and effort. Numerically higher gears will require an ECU workaround, which isn't super easy from what I understand.

 

I am not so much interested in the ratio change as I am with the LSD capability. I drive a lot of lower speed roads and have lived with the "one wheel peel" in other vehicles...which I'm sure is easy given the instant torque from the supercharger.

 

XJ40/X300 LSD will fit, as you've learned the pinion it offset; the stock driveshaft will not work, and the XJ40/X300 shaft is arranged much differently so anticipate some rework and be mindful of maintaining proper alignment. My setup is a custom one-piece shaft to accommodate XJ40 LSD (LS/T56 swap).

An LSD may be tricky to find but not impossible; X300 XJR will have 3.27:1, an NA car should be 3.58:1. You can ID a PowerLok by the black X across the color code that denotes gear ratio (pic attached). Search YouTube for "XJ8 Sport Upgraded axle swap" for a video about it also (not mine - posted a link but it popped in a huge video). I swear there's a guy that put an aftermarket Ford locker in the X308 14HU, but can't seem to find it. Quaife might be worth a look also.

 

Ecm and tcm reads drive speed from rear abs sensors. Quaife makes lsd to the x100 / x308 diff. All x308's are open diff only. To my recall the video dude put ford locker on HU15 not 14

 

So if I install a 3.54 from an older X300 and the rear wheels are spinning faster than the ECM/TCM expects, I assume there will be limp mode/malfunction lights?

Sounds like the only option is to stick with the factory X308 ratio and try to adapt the LSD.

 

Good call on both, it was the same guy too; Search YouTube for "Dana 44 8.5 to 8.9 conversion on a jaguar rear axle x308 x300 mods".

 

the benz trans has no output speed sensor, it uses rear wheel speed message from the ABS. Chirpy made a CAN spoofer to change your gear ratio. idk if he still makes them but definitely uploaded the basic code to do it out of an arduino.

long story short the XJ40/300 diff pumpkin will bolt straight in as long as you use the trapezoid plate for it, the driveline angles are fine. if you want to use a different carrier just know the GKN HU diffs changed to metric thread, I think it's M10 so any 3/8 D44 carrier is going to have to be drilled to take your donor ring and pinion.

 

You can swap in an HU15, but it's not trivial. Do your research first, and then decide if it is worth it to you.
Using an X300 XJR rear end is the best starting point. Most of the XJR X300 rear is the same as XJR X308, except for pinion offset, wishbone tie, pinion flange, and anti-roll bar (but bar is easy to swap over)
See Baxtor's write up on X100 conversion (rear end is essentially the same as X308) https://www.jaguarforums.com/forum/x...change-251133/
You need the HU15 diff and the front plate with the offset hole for the diff nose.
If you don't want to turn down the HU14 bolts through the wishbone tie like Baxtor did, you also need to obtain and use the XJR X300 wishbone tie, spacers, and bolts.
You will either have to get a custom driveshaft made to work with the existing HU15 Jurid/Guibo/Rotoflex 3 bolt flange, or swap to a bolt on flange (10 spline pinion XJS 4 bolt flange??) plus spacer, like Baxtor.
If you keep the 3.27 ratio from the XJR X300, then you will need to address the ratio change issue with the TCM (reprogram (good luck on finding a source and paying for it) or spoofing box (no I don't make them, but I made the instructions available for DIY))
If you change the ratio back to 3.06, then you will probably have to use Dana 44 ring and pinion (they do fit) and suitable bearings to do so since inner diameter for outer pinion bearing is different (I don't think there is a Salisbury 3.06 solution with extended jurid pinion shaft).
With Dana 44 then the pinion input shaft changes to 26 spline, so you then need to solve the driveshaft to pinion connection with appropriate flanges.
With Dana 44 you also then have option to use various Dana 44 locking carriers like Auburn, Eaton, Speedmaster, etc. (make sure you get 19 spline output shaft version, not the more common 30 spline, and note that the carrier bearing diameter will probably be larger (1.795) like the Dana 30 spline, rather than the Salisbury carrier (1.6875)).
If re-using the HU15 Jaguar carrier, then the clutch plates will almost certainly need refreshing.