problems with 4WD

Ive been searching through threads on problems with 4wd. One thing I keep seeing as the common problem is the vacuum line but im unclear what the vacuum line actually does. When I engage the 4WD, I can hear (at least what i think i hear) the hubs locking but the front tires do not spin. I havnt been able to look at it too much cause I just noticed it and its snowing pretty hard. So basically, im wondering where does the vacuum line come into play? And also where exactly is it located? Any help would be appreciated cause the 4WD feature is why I bought the truck and it would be nice if it worked

I can't tell you the exact location of the vacuum lines because the placement of various pieces seems to vary from year to year. Basically there is a line (probably these are 5/32 in) from a tee on an engine vacuum line to a switch on the top of the transfer case. Depending upon year, there may be another vacuum switch mounted on the firewall. Then from the transfer case switch to the actuator for the front axle, located under the battery. What I think you are hearing is the encoder motor on the transfer case. When you select 4wd, the encoder motor moves the switch on the transfer case, sending vacuum to the actuator for the front axle, which pulls a cable to move a shift fork in the front diff. See if you have transmission fluid in the vacuum lines. That's a sure sign the transfer case vac switch is bad. Part is $10-15. It is not too hard to replace if you can get under there. My work area was about 4" deep in water, so I had a shop replace mine, they charged $36 labor.

oh thats not bad at all, hopefully that does it, thanks for your help

You're welcome. Good Luck!

The transfer case switch was my problem too. Pain in the butt but 4 wheel worked like new when it was done. The check ball in the switch was stuck open. The part was $32 at the dealer.