4 Wheel drive out, but everythings engaging
 

I have a 96 Blazer 4x4. got 136,000 miles one it. I can push my 4x4 low and 4x4 high button and i can hear my lockouts engaging. And my front drive shaft is turning also. I am not getting any movement from the front axle to the hubs. I was told by some guys that goes to an auto tech class to check the thing that is connected to some wires that bolts to the front axle. and it my not be engaging the 4 wheel drive. I dont know what the exact name of it is. And i dont know how to check it yet. Does anyone know what im explaining. And any ideas of how to check it. Thanks

There is a vacuum actuator (underneath the battery tray usually) If you can and know how hook up a vacuum pump and test that. Commonly either there is a vacuum leak somewhere, vacuum switch is bad, or if the 4x4 is not used very often the connecting gear will get stuck in the open position.