Moderator

Over the years I have thought long & hard about this & I honestly think that it is a very complex issue.

This is compounded by the price of suitable LSD units, Peloquin to name but one, last time I looked they were about 1000 pounds each

Front LSD
It seems to me (from a laymans point of view) that as the syncro (mechanical) 4WD system is activated by at least one of the front wheels/tyres slipping on the road (wheelspin)
this then creats a rotational speed difference in the VC Unit which then causes the VC to lock up,
putting up to 50% of the available power to the rear wheels thus reducing power to the fronts & controlling the wheelspin.
Whereupon as now the front & rear wheels are rotating at the same revs the V.C unit now ‘unlocks’ & you are back in FWD again.
So, I think that if you have a front limited slip diff you are reducing the revolution differential in the VC unit by transferring the rotational speed difference (wheelspin) from one front wheel to the other instead of transferring to the VC unit & the rear wheels.

Rear LSD
Now for the rear diff, yes I have actually seen a syncro stuck in mud on a beach & going nowhere with 1 front & 1 rear wheel spinning due to the standard open diffs, would LSD front (and/or rear)have made any difference? I don’t know, but I dont think so, I might have been watching a car with all 4 wheels spinning, highly entertaining but basically no different outcome!

Of course when the front & rear revolution speed equalised (with both front & rear spinning) I would think that that the VC momentarily shut down only to re-engage very quickly when the rears stopped (btw the VC unit engages within a 1/4 of a revolution or 1/5 of a second)

Personally, I would think that a LSD on the rear axle may be of more benefit than a front unit, as it would allow the Syncro systen to function as designed, & move power to the rear wheels, but at a what a cost for an LSD to control at maximum 50 % of the power.
BTW I have looked at the Peloquin website this evening & I am not sure that the rear LSD it still available.

We need an automotive engineer, or at least a grown up to make a definite statement on this matter.