4 Wheel Drive/SUVs: 4-wheel drive wont engage, jeep cherokee, vacuum motor

Question
I have an 1986 Jeep Cherokee the four wheel drive will not engage, and honestly has me stumped, it has the vacuum to the line going to the Actuator on the axle, so i am wondering, could it be the the transfer case switch or the actuator? or anything else?

Answer
Tim,

First thing to check is the vacuum motor on the axle.  These are notorious for plugging up, hanging up, and just plain not working.  They are not hard to check.  You can pull the cover easily and visually inspect the shift fork and see that the slide collar is working smoothly.  Many, such as myself have converted this vacuum system to a cable shift.  
One way to check this is to have someone put it into and out of 4-wheel drive with the cover off and see if the shift fork moves back and forth.

Carl