Series 1.5 4.2L diff failure

[Freoway]

I have a 3.07:1 limited slip diff in my E-type. Car had been off the road for a couple of decades. I foolishly did not check the fluid level in the diff before doing its first drive last week (I thought I had!) after a major rebuild (diff not included in rebuild). Car drove 10 kilometres before a minor whirring noise started and shortly afterwards, the diff locked up. I've jacked up the car but haven't dissassembled anything yet. I'll probably need another diff. The wheels spin freely (in opposite directions of course), but when attempting to drive, the diff appears frozen. No power through the rear wheels. Handbrake and brakes work fine. I'm consigned to the fact that my oversight is an expensive mistake. My question is, what is likely to have failed first? Gears? Clutchpack? Bearings? Everything at once?! Note that the rear wheels spin when the car is jacked. I'm hoping someone who is familiar with this LSD may be able to answer.

[mgcjag]

Something odd here.. if you have a lsd then with the rear jacked up if you turn one wheel the other turns in the same direction....without lsd it will turn in opposite direction....if you do have a lsd then no oil has probably caused the clutch pack to wear..however you need it out to check what other damage has happened as you say it locked up..you could have chewed up bits of metal anywhere....Steve

[44DHR]

Lloyd,
I’ve been giving this some thought and wish to question your comment about “the diff locked up” or “appears frozen”, yet the wheels still spin freely in opposite directions.
The Salisbury Powr-Lok differential operates by a series of clutch plates held in compression by an outer Belleville dished spring washer on each side of the clutch plates. When the car is jacked up, the clutch packs are compressed together sufficiently to lock both output shafts to enable both wheels to normally spin in the same direction, unlike a conventional differential where each wheel moves in an opposite direction.
Without oil - and the correct oil with additives - these clutch plates can quickly overheat or get scored, plus the end Belleville dished washers can crack and lose all compression making the clutch pack defective. Possibly - I have not considered this before so bear with me - without any form of clutch pack, the differential would become like a conventional differential as the four internal gears on the Bevel pinion mate gear assembly would simply turn the bevel side gears on each side in an opposing direction ?
I am assuming when you can jack the car this is what is happening with both wheels free to turn, but then you state that the “diff appears frozen” with “no power to the rear wheels”. This could be a result of the drive pinion being seized in its bearings, or the drive pinion somehow being locked to the Crown Wheel through some form of debris. So, effectively the prop shaft can’t turn the differential, yet internally the two output drive shafts can rotate - albeit in the conventional direction.
Just my thoughts, but the only effective way is the open up the differential to confirm that you have indeed a Powr-Lok diff and exactly what potential damage has happened.
Regards,
Dave