4wd not engaging

[Treadted2]

My 4wd isn't engaging when I flip the switch. I hear a hiss from the vaccuum, but nothing else happens. There is also a his when I switch it back to 2wd. Does anyone have suggestions for where look for problems? Thanks

Ted

[Dive 30]

It's actually a pretty simple system. There is a vacuum feed hose that comes off of the vacuum reservoirs (little black ball on firewall) from a tee. It then runs to the middle of the switch on the dash with the two (yellow and green?) harder plastic hoses running from the switch to either side of the 'vacuum motor' which is just a vac operated piston. Put vacuum on one side, goes one way, put vacuum on other side, goes other way. I'm not sure about the vacuum supply for your front diff (mine doesn't have that) if so equipped.

I suppose I would start at the supply and work my way down.

Hope that helps.
Phil

PS: Mine hisses also when switching from one to the other. I think this is because the line that just lost vacuum is equalizing. It should only do so briefly though, if it is continuous I would suspect the switch.

[Brown Bear]

The his should happen when you flip the switch. Is it hissing for a second or two and then stopping, or is it continuous? Will the tcase go in 4lo? If it won't even budge out of 4hi then the likely hood is that you something is amiss in your vacuume hoses. Mine wouldn't budge and it turned out that I had a broken hose on the firewall in the engine bay. Check those first. If you have a vacuume pump and some hose you can check the switch itself. Mine also leaked for some time. An easy way to check the switch is to take the vacuume plug off the back of the switch. There are three holes. The middle is constant vac. source. Take a hose and some sort of connector and hook it from the center hole to the left hole and then give it a try. If all of these fail, I would then check the vacuume hose leading to the front axle. Hope this helps.

Brown Bear

[Kimbrough]

Check your linkages from underneath. Simply grab the linkage that goes into the vacuum motor and move it with your hands. Should be fairly easy to move. If not, its frozen due to lack of use. Squirt some oil in there and see if it helps.

I had a broken vacuum line on TOP if the Tcase - just under the trans tunnel. Good Luck!!!

[Dome]

Probably a vacuum problem, check for leaks in the lines, also check the vacuum motor down by the transfercase. These vacuum systems are a real pita in my opinion, thats why I converted by Selec-Trac system to a manual shift lever, no more guessing if I am actually in 4wd or not. There is some kind of reading tool that will test vacuum, I've never used one but maybe you cant rent them from a hardware store or something.