With the Jag IRS out of the car, I could strip the 4HU LSD and shim the springs to tighten the diff. The diff has never been measured for the breakout torque, but now it was 25ft.lb, I want to aim for around 75ft.lbs.
The breakout torque is measured across the two output shafts, here one output shaft is held by a bar pressing on the workbench and a torque wrench is used to measure the torque on the other driveshaft. The torque wrench is slowly turned up until the diff starts slipping rather than the wrench clicking at the requested torque.
Removing the diff cover, shows the LSD.
The LSD is removed and dismantled, revealing the clutch plates and the spring plate.
Two of the clutch plate splined to the output shaft are back t back so as they have no movement relative to each other, this is where I added the shim on both sides, cut from an old oil can.
Adding the first shim the breakout torque was raised to 45ft.lb, so I doubled the shim thickness but the LSD was locked solid. I got out my engineers shim plate and trying a shim at 1.5 times the thickness of my first resulted in 65ft.lb