Hi Dave good to see you back on the road.
I don't think the thumping that you have is caused by the center diff. More likely slack in the drive line or in the suspension, that winds up,when the brakes are applied.
The fact that the fuse stops it, can be that with the diff locked, the drive line is bound up, to remove the slack.
I am sure it is not in the center diff. The way the diff works is a bit hard to explain, (it still varies the torque without running,) but when the car is travelling in a straight line the diff spins as a solid unit, just like the gears in a normal rear diff. It is only when turning, or wheel spinning that the gears actually revolve.
It would take a lot of wheel spin, front or rear to get the gears to revolve fast enough to destroy them. This is how they broke it in the first place. Lifting the front and towing it on the back wheels.
All AWD Subes must be 'all up lifted'.
The small difference in the rolling dia. of the front/back wheels would not affect it to any great extent, as the diff will accommodate it, as the Limited Slip Clutch is not applied. It is different to the Transfer Clutch system which cannot accommodate too much difference in wheel dia. as the clutch is applied and has to slip to do it.
The fuse is used for running the car on the dyno. It locks the front and rear together to prevent shunting between them, on the rollers.
Don't worry about the AWD, just look for the brake problem.
Harvey.
