Sometimes they shear clean and other times shatter like yours. Use a new diff gasket, do not use sealant like some do as puts diff slightly out of place.
 
I used the gasket with blue hylomar.

All back together and driving again, but I think I may still be stuck in difflock from when I drove it home broken.
As I reversed into a space at work I got abit of a judder, vaguely remember something similar when I was stuck in diff lock and needed to reverse around abit to unlock, I don't use diff lock at all really.

Got my jack with me and parked on the flat,
If I jack up one front wheel it should spin if diff lock off but not if diff lock on, is that correct?
 
I used the gasket with blue hylomar.

All back together and driving again, but I think I may still be stuck in difflock from when I drove it home broken.
As I reversed into a space at work I got abit of a judder, vaguely remember something similar when I was stuck in diff lock and needed to reverse around abit to unlock, I don't use diff lock at all really.

Got my jack with me and parked on the flat,
If I jack up one front wheel it should spin if diff lock off but not if diff lock on, is that correct?
That's right.
 
Reversing in a straight line is usually enough to get a reluctant lock to release. Do you have a working diff lock light?
Even if you have no every day use of the diff lock it is good to exercise it now and then, getting it in and out on say a gravel car park or a grass verge.
 
Front wheels both spin fine with the opposite wheel still on the ground so I don't think I'm in diff lock anymore.
Drove back and forward about 10 times or so a fair distance and couldn't replicate the judder I got, handbrake not completely off or not in reverse properly earlier perhaps.
 
Stopped driving the defender for abit, Last time it did do the judder in reverse again as I was parking.

Jacked up one back wheel with the handbrake off and out of gear,diff lock off.

Tightened the main handbrake shoe screw till it catches and then backed it off a little, get 5 clicks and does hold well.

What I've got happening though is,with the handbrake off, the one jacked up rear tyre rotates freely backwards but seems to have abit of a 'stop' going forwards, easily overcome pushing a little harder but I can't imagine this is correct.


I've checked the rear drum brakes and they're adjusted up properly still (renewed a couple years ago)

Ujs feel good to me, I regularly grease them
 
Might be worth checking the spring in that drum is pulling shoe back, could be slave piston getting stiff.
 
Finally got to the bottom of this,
Jacked up two wheels on the same side, with diff lock off they should both rotate freely, mine did not .. rotated but kept 'catching' the other wheel and then started turning that too .. with quite abit of rattle and clunking.
So diff lock not fully disengaged and kept catching, worse backwards which explains why it only made a bang reversing full lock.

Kept pushing the difflock lever side to side quite forcibly and both wheels now turn independently very smoothly without any noise and no bangs in reverse.
 
There is a small lever on top of the transfer case (easily accesed by removing the covers under the drivers and middle seat) which turns the High/Low and lock on and off and also finds neutral.
The levers/pivots have worn or are loose.
Its easy enough to fix.

Here's a pic..
Hi - Lo -Diff Lock Linkages_movement.jpg
 
Another issue can be the bracket on the 3 bolt housing [ bottom of pic] coming loose. I know because it happened on mine.
 

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