I have changed the solenoid on the transfer case, the vacuum diaphragm, and all the vacuum lines for the 4wd system. the diaphragm worked at first but lost vacuum at the diaphragm. what the??

 

Some more info about the truck will help to figure out the issue. What year is it, and is it 3 or 4 button transfercase

 

2001, 3 button. after replacing the vacuum lines, the vacuum actuator worked, for about 5 minutes then right back to no vacuum at the actuator. I have good vacuum going to the transfercase, and I have repaired the vacuum leak by the master cylinder earlier because of my heater controls not working. sooooo???

 

Just to be thorough, have you checked the rest of the vacuum lines under the hood for leaks?

Perhaps you can temporarily bypass the rest of the vacuum actuated bits and hook up the vacuum directly to help you isolate the problem; i.e. either with the 4wd system vacuum or the rest of the vacuum system.

 

I would start by tracing back the vac lines starting at the actuator to make sure none of the connections popped off/aren't fully hooked up. I have had problems with the short vac line that connects to the canister in the driver's fender coming off before

 

the only hose I did not replace was the vent hose from the back of the transfer case. I couldn't get to it. I thought about running a separate vent line for that and plugging off where it goes into the vacuum system for the transfer case to simplify the system. I have great vacuum at the source for the transfer case, would that be the case if the line came off the canister? I'm not going to mess with it until after Christmas but keep the suggestions coming i'll take all I can get!!

 

from what I have experienced , If the line comes off at the canister you still have reasonable vacuum but not enough to lock the front diff....the actuator still pulls the cable but not enough to lock.