Well apart from the lack of 4wd in reverse, the absence of the vacuum actuator gives the freewheel lock plate the freedom to move back and forth resulting in a locked position while for example, sharp cornering to the left and an unlocked position while sharp cornering to the right!
The Locking-plate (below) slides over the splined shaft
and then Is free to move and engage the free-wheel bolts (below)
I have had this when the nylon push-rod of my vacuum actuator was broken. Some times I noticed a strange clicking sounds when reversing on slippery ground and when cornering. When I finally opened up my rear diff, I noticed the problem and it had caused some damage to the free-wheel locking bolts, and chipped off a piece of metal from the free-wheel locking plate, resulting in some minor damage to the crown-wheel (some scarring).
So to be honest, if I were you, I would change it pretty soon!
