I don't think my truck is going into 4wd. I don't get an indicator light at all when in 4 hi or 4 lo. I heard today that the transfer case runs on vacuum. I have all the vacuum lines on the right way.
In September I had to change the egr valve and I ended up pinching a vacuum line under it when I put it back on. When I figured out what I had done I went to fix it. The side that was still connected to the motor had plugged itself by melting closed. When I cut the end off to do the repair it let off air pressure, like a compressor would do when you release the valves. Is this something I should have worried about then? Is this the reason why my truck won't go into 4wd?
Also when I was under changing the crank position sensor I had a vacuum line that had a valve on it. When I moved it, it broke off. I checked the valve thingy and you could blow through both sides. This thing is located on top of the tranny running in the same loom as the vacuum line for the tranny. I just thought it may be a releaf vacuum line. Is this something that I need to worry about or could that be my problem? How many vacuum lines run to the tranny and transfer case?

I really need to get this fixed ASAP. I got stuck in the middle of the road today. AND THAT JUST LOOKS BAD ON US DODGE OWNERS! Good thing I had a friend with a working 4wd in his dodge ram.

 

is it clicking in the axle when its tryin to engage? most likely its your cad unit. that has its own vaccum and its prolly gone bad. mines out too. just order the posi lok and begone with the vaccum design all together

 

No- No clicking when trying to engage. It don't make any sounds when I put it in 4wd. I know the front wheels are not pulling though. This CAD you talk about, how hard is it to get to or work on? I don't post here enough to know what everything is, LOL. I uaually call my certified mechanic friend, but he is busy and don't have time to look at it.

I am just thinking I broke a vacuum line or something to it. It worked last year, LOL. IDK

 

There is one line that comes from vac, 2 lines that go to 4X4 and the other normally just has an open end behind the engine block. My 1500 has always been a little shy on vacuum. I replaced the vac valve for 4X4 for about $25. But no worries if you just change it out to posi lock.

 

What is a posi lock?

 

Sounds like a vacuum line to me. Check the lines where they change from a plastic line to a metal line by the transmission and at the front axle. The rubber piece that connect the two lines gets loose. I used a couple of zip ties around the two ends of the rubber pieces to snug em back onto the lines. I had the same thing happening to my truck about two weeks ago and that's how I fixed mine. I could've bought new rubber pieces for a few pennies at the parts store, but the zip tie were a quick fix and it worked out good at the time. Hope this helps you out.

 

take the 2 vaccum lines of the lil motor on the front axle..spray some wd-40 in there..i had that issue to..i sprayed it in the lines and never had a problem with the 4wd since

 

the two lines coming from the diaphram looking object (actuator) on the axle go to the t-case (IIRC) .. those are common to rot out.. they did for me... they go from soft lines to hard steel lines.. the steel section is what went for me.. rotted through and lost my vacume.

if you have a vacume problem then your heater controls (floor/defrost) will be a bit goofy.. when my controls started to act up thats how i realized what was wrong.. my defrost would stay in defrost untill i smashed the gas.. then i heard the door in the core flappin around...there is a 3 line vacume connection on the passenger side engine compartment near the PCM/tranny dip stick.. check that too.. that line feeds the controls and something else (not sure what the other line goes to)

 

Thank you for all those tips guys. I will check all that out and let you know what I find. A BIG Thanks again.

 

Reading this thread today because my 1995 2500 has the same problem. Wondering if you got yours fixed yet and was it a vacuum line issue? Haven't needed 4wd until today. Got about 10 inches of snow last night. I had someone do the plenum gasket kit job a few months ago. I'm wondering if they left off a vacuum line somewhere.[:@]