The way I understand it your transfer case is always turning the front drive train right up to the axle itself which is then engaged or disengaged bye the little actuator on the axle. So when you shift into 4WD what does it change in the transfer case???

Keith

 

its the other way around your diff is turing your drive shaft, but its disengaged at the t-case, untill you move the lever.

 

i thought that the drive shaft doesnt move period. untill you lock your hubs.. then it will onyl turn with the fron axel`s movement. unless you dont lock the hubs and put it into 4wd. then the drive shaft will turn but not provide drive to the fron wheels . only when hubs and 4wd are used together is everything a nice union.

 

Ok. That makes sense. Then what does that little vacuum actuated device on the axle do if it doesn't engage the front axle?

Keith

 

On a 99 no locking hubs and he would have a CAD system so it operates like this. 2wd mode the front drive shaft does not turn. 4wd the trasfer case locks the front drive shaft in and it turns same as the rear shaft does. The tranfer case vacuum switch then sends vacuum to the CAD which locks the right axle to complete the switch into 4wd.