I had an issue With my heater control switch hissing. I changed it and in the process i realized that there was fluid in some of the colored vac lines that plug into the heater control switch. i look under the hood at the 4x4 vac lines and they also have a small amount of fluid in them.. I researched other forums, and came up with the imput shaft seal on tranny being bad which lets the t-case fill up with atf fluid, and at the very top of the t-case there is a type of vacume switch that sucks up the fluid introducing it into the vacume system. Now i took out the fill plug on my t-case and my t-case is not over full past the fill hole so im guessing the fluid has not touched the vacume switch at the top of t-case... So my question is does anybody know how else the fluid could be getting into my vacume system?

 

If the transfer case input shaft seal leaks, transmission fluid will enter the transfer case. If the vacuum switch leaks vacuum, fluid will be sucked into the HVAC & 4WD vacuum systems. As you can see in this image, the vacuum switch is nowhere near the top of the transfer case. Even when the transfer case fluid level is correct, the switch is very close to the fluid.





If the problem is not taken care of right away, the transmission fluid will deteriorate all of the rubber parts in the HVAC & 4WD systems: Vacuum lines, actuators, HVAC mode switch, etc. It all needs to be thoroughly cleaned out, or you'll have ongoing problems with both systems.

 

So considering my trans fluid hasnt made a, noticeable drop and the t-case seems to be a little low. Do you think its just a bad vac switch on the t-case and not the input shaft seal?

 

The clue to a leaky input shaft seal is low transmission fluid level, along with high transfer case fluid level. I think you can safely assume that the switch is the problem. You still need to clean out the two vacuum systems: actuators, lines, reservoir, HVAC mode switch etc.