i have an 88 xj with the command trac , with the vacuum disco axles ,and i also have a 87 wagoneer with the 242 case , so heres the question i want to swap in the 231 case in the 87 as the body is in much better shape both are aw4 trannies , and i already have a A/A sye kit for the 231 but it the tail housing doesnt have the vacuum swith provisions as i bought this kit for my tj so the question is what does the vacuum swith really do does it just for the axle and can i use the sye kit and not worry about the the switch as the waggy doesnt have vacuum disconect axles