My 4WD didn't work for few months till I had the time and found out it was a vacuum line out of it's place at the vacuum switch on the transfer case, so I plugged it back and it worked for months then it started disengaging and reengaging sometimes as I would drive in 4WD, then it stopped engaging at all. Today I had the time to check it out and found all lines in place. I tried bypassing the switch by unplugging the vacuum lines from the switch and coupling them directly, and it engaged at once. I tried to blow/suck through the switch to test it if it's opening and closing, and it seemed working fine with minor leak when it's closed (keeps vacuuming from the actuator line). I also connected the vacuum line to it, and it did work fine opening and closing the vacuum through it (tested it with my finger tip).
What could the reason be that the 4WD is not engaging through the switch but works fine when I bypass it? Could it be a faulty switch or a weak vacuum, and how can I test it?
Thanks in advance guys!

 

OK. I think I'll just change the vacuum switch as it has never been changed before, anyway it's leaking some vacuum when in closed position.

 

Check out the first page of my build thread it shows how to take care of the vacuum issue in the 4x4 system forever. Still one of the best mods I have done to date!!!

 

Today I noticed a hissing sound from the transfer case area that goes off when I shift to 4WD, so I took a quick look (again) and found out that the 3rd line from the vacuum switch that joins another line from the transfer case (or transmission, I can't remember) is cut or unplugged with 4 inches of it left plugged to the switch, and I couldn't see where the other end needs to be plugged and didn't have the time to dig in... Any help?
Rexmburns! Thanks for your reply! I like what you did! I think I'll do it when I have the time to, but will need to see if I can find a good cable with the proper length to use for the mod.
Few Qs: when you pull the cable, does it stay pulled without slipping back, and how do you know you're not pulling too much, can you feel a "stop"?
If you forget it pulled and switch back to 2WD and drive; will that break anything?

 

Its a locking cable. So basically how it works is you turn the cable 1/4-1/2 turn counter clockwise to loosen it then pull on it good and solid but don't yank on it! Once is pulled out you just turn it back clockwise till its locked in place. I think the only thing you would damage by pulling to hard is how you have it mounted and attached. It really doesn't take that much force to make it work though. My wife has engaged it several times with no issues. As far as forgeting to disengage it you still have to push the buttons on the dash to engage and disengage the transfer case so you just have to remember that when you push the button you pull the cable and when you pull the cable you push the button so when the cable is pulled the button is pushed or when the button is pushed the cable is pulled. Lol just playing its really simple to use and works everytime I love it plus the best part about it is that you can put the t-case in 4low and not engage the diff and then you can crawl around the slower trails in low gear but still be able to turn and manuver as if you are in 2wd. I think the link for the cable that I bought is somewhere on my profile page if you can't find it let me know and I will post it here for you as well.

 

I think I'm going to do the same mod you did, but what should I do with the vacuum line that was running to the vacuum switch, should I close it or leave it open with a small filter at it's end? And as I read in some threads, the vacuum switch has 3 lines. One is the vacuum, one goes to the actuator under the battery, and the 3rd couples with another one coming from the transfer case and ends up in the engine compartment. As I mentioned previously; the 3rd one on mine has only 4 inches left attached to it with nothing on its tip (no coupler or anything) and can't figure out how to find and reach that transfer case line. Should I be worried about leaving the coupler and that line that comes from the transfer case open, knowing that I do some offroading in fairly deep water?