Jaguar Rear End (IRS) Specifications

Model		Year	Gear ratio		Width
E Type		61-75	3.07,3.31,3.54		* 52"
Mk 10		61-75	3.54,3.77		* 60.5"
S Type		63-68	3.54,3.77		* 55"
420		66-68	3.54			  55"
420G		66-70	3.54,3.77		* 60.5"
XJ6 4.2l	68-85	3.31,3.54,3.77		  61"
XJ6 2.8		68-85	4.09,4.55		  61"
XJ12		72-85	3.31			* 61"
XJ6/12 S3       79-92   2.88,3.07                 61"
XJS		75-96	2.88,3.07,3.54		* 61"

* = Factory Posi

XJ6 – 69-73 (Series I)
Girling Callipers/1/2″ Rotors
Ball Bearing Stub Axles
3.54 Gears
61 3/4″ wide

XJ6 – 73-79 (Series II)
Girling Callipers and 1/2″ Rotors but with Odd dust Cover
Tapered roller bearings on Stub axles standard 3.31 gears with locker optional
61 3/4″ wide

XJ6 – 79-88 (Series III)
Girling Callipers 1/2″ Rotors
Tapered roller bearings on stub axles with Drain hole in Stub axle flange
2.88 Gears Locker optional
61 3/4″ wide

XJ6/XJ40 – 88-95
Completely different set up, not recommended for aftermarket applications

XJS – 76-87
Girling Callipers 1/2″ Rotors
All Powerlock Gears
Tapered Roller Bearings on Stub axles
3.31 Gears
61 3/4″ wide

XJS – 87-89
Girling Callipers 1/2″ Rotors
Flat bottom diff with NO drain plug and 3 bolt mounted stub axles
American Dana Unit with weak traction lock (Not recommended)
2.88 Gears
61 3/4″ wide

XJS – 89-95
Girling Callipers 1/2″ Rotors
ABS on uprights/speedo pickup in rear aluminum diff cover
2.88 Gears
61 3/4″ wide

16 thoughts on “Jaguar Rear End (IRS) Specifications

  1. Good information, but am curious about the 3.07 listed for Series III XJ6/12. My 85 Jaguar Sovereign European version is stamped 3.058 on the differential tag. Did you round this up to 3.07? Or is the list for US jaguars only? I believe the Sovereign’s diff is also limited slip.

  2. Thanks for the input. I never have checked out a Sovereign. good to know it is a posi. These spec are all US (i think)

  3. Hello, I am finding different info regarding the last of the xjs model with 6 0.L v12 and 4L80E trans final drive gears. 2.88 :1 or 3.54 :1. Since the different trans has over drive and starts in second unless the sport switch is on. I can’t know for sure the true ratio short of pulling it out of my car and looking at it.

  4. Russ, you don’t have to pull it out to check it.
    Simply jack up the rear, block one wheel from turning, put a mark on the driveshaft and a mark on the free turning wheel. Engine off, car in neutral, count the turns of the driveshaft it takes to make one exact turn of the wheel.
    Done.
    Cheers, Kurt

  5. I’m trying to ID a Jag IRS. Where did you get your spec table? The widths for E, 420 and S do not match other tables (Daze, Wiki), which also do not match completely. Help…

  6. Hey Cal, The width measurements are not an ideal way to ID a jag rear. The width changes drastically when they are removed from the vehicle and they are quite difficult to measure while in the car.

    A removed Jag IRS will be about an inch shorter, so allow your measurements to have a little wiggle room when you are identifying.

    Another thing to note.. If you are installing in some project, you may want the half shafts(upper control) flat with the ground for best geometry, which will be about 3/8″ wider than the slightly downward angle in the original Jag configuration. I have found this configuration to provide much better camber when cornering.

  7. Useful info on ratios but according to the Mk10/420G workshop manual UK spec cars sold in Europe were fitted with 3.31 ratio diffs

  8. I have several Jag diffs here and with odd numbers. One is 3.058 out of a “85 Sovereign which is self explanatory. The other has 7.5 on the tag. This has me baffled. Any clues on this and it’s origin?

  9. replica cobra running old s type diff producing around 350 horse power
    diff ratios to low,any suggestions on a suitable replacement

  10. Hi Frank. Sorry about the delay.
    Just sold the last of my stock.
    Have Powerlok V12 but will keep that.

    Cheers.

  11. I just purchased a complete rear with 78 I Ia Lost. The Vin no is-SAJAY12L9CC334678. I need the gear ratio THANK YOU.

Leave a Reply

Your email address will not be published. Required fields are marked *