I tried to go off roading today in mantua, ohio, but it didnt go too well. Turns out all of my buttons to engage my 2wd, 4hi, and 4 lo, all say they are engages when i press the button. I even hear the transfer case switching between them all. But when i actually got to try it out... i only had 2wd. I switched to neutral and then 4 low then rocked it a bit, and it was like it was in 2 lo, lower gear ratio but still no grip from the fron 2. I pulled out my battery and moved that vacuum actuator so i can access it while the motor was running. I have good vacuum. so i hear the t case working, i have good vacuum. I took it to a shop after and they said it was the front diff. me and my buddy can put a new one in but any other ideas? btw, when the vacuum plunger thing is sucked in, this should mean im in 4wd right? since it pulls the pin on the differential out? because if i start my car in 2wd the thing is already sucked in, and wont depress after i shut it off unless i work it. afterwards, it will get sucked in switching from 2 to 4, but after going back from 4 to 2 it wont depress...whats it supposed to be doing. Also i heard a 96 to 98 bravada part works here to eliminate the whole vacuum system

 

I think I'm having a similar problem, it sounds and the lights looks like it engages to 4x4, but I think only three wheels are powering based on some field experiences. My suspicion is the differential bearing on the passenger side is bad. But I hope someone can help us both out with some advise.

 

It probably is the front diff, its the vacuum actuator. Take out your battery, and your battery tray, there is a little vacuum thing there (bolted to the fender well), it has a cable coming from it, see if the seal is ripped or if the vacuum line has come off.

 

My problem ended up being that a vacuum line was disconnected, reconnected it and it works fine again.

 

Lost control of heat selector, blows heat when off, hissing from dash. Replaced selector control & vacumm harness, most all vacumm lines & now have oil in vacumm hoses , problem is back? 2002 blazer 4x4

 

Check your transfer case to see if it is overflowing with fluid. There is a seal between the transmission and transfer case that may be leaking. It will fill up transfer case with tranny fluid, then the fluid gets sucked into the vacuum lines. Do a search for under dash vacuum lines. I hope that helps.