hi i have a 94 s10 blazer w/ 4x4. when switching from 2 to 4 i feel it click into gear in the treansfer case but my front diferential dosent lock. ive been told that i might have a bad vacuum switch on the case itself but i dont have a clue. any ideas. thanks, john

 

It could be the vacuum switch, however you need to check the accuator located below the battery box. In 4hi or 4lo while the engine is running the accuator diaphram should be pulled in by vacuum, which will pull a cable that engages the front axle. If the accuator is not getting pulled in, then you need to see if the vacuum line connected to it has vacuum on it.

If there is vacuum on the hose at the accuator, either your accuator is bad or your cable is stuck. You can remove the clip that attaches the cable and pull on it to see if it moves. It should pull a couple of inches fairly easily.

If there is not vacuum at the accuator, then you need to check for vacuum at the transfer case switch. If there is not vacuum at the tc switch, you have a leak between the engine and the tc switch.

If you have vacuum to the tc switch, then either the switch is bad, or you have a leak between the switch and the accuator.

The vacuum switch is located on top of the transfer case above the front output shaft and has 3 vacuum lines hooked in the top.