I had two issues with the four wheel drive when I got the truck:
4wd light flickering on and off
4wd didn't seem to engage / disengage properly.


There are two vacuum lines coming from the CAD, a red and a black. I found that the red line at some point in time was rubbing against the drive shaft... fixed that and everything seems to be working as it should... I think.

So now I feel the vacuum at the red line but not at the black line, so I guess my question is should there be a constant vacuum at the black line?

 

there should be vacuum on one of the lines when the t-case is in 2wd, and vac on the other when in 4wd.

the vacuum pull on one side or the other of the vac diaphragm, which pulls the fork and collar to engage or disengage the 2 axle halves.

there is a vacuum control switch on top of the t-case. one vac line from the engine feeds it. it switches the vac to one or the other of the 2 outputs. the 4th line is a vent.

if you have any bad lines, just run 2 new hoses from the cad to the t-case.

see here
http://dodgeram.org/tech/repair/4X4/4x4_engagment.htm

 

Thanks for the reply and the link, everything is working as it should.

Dan