box on front axle of 88 xj?

i'm striping an old jeep i picked up and on the front axle passenger side theres some sort of a box on it right, beside where the control arm attaches. it has a vacumn hose or something going into it anyone know what its for? its only on 1 out of the 4 jeeps i have.

it is the vacuum motor for the disconnect axle shaft. It is a 2-piece shaft that actuates with a collar.