i have a 94 blazer 4.3 vortec. the 4wd workd great. then one day the front diff started unlocking on hard wheeling. i was told i was losing vacume so i bypassed the accuater under battery. it worked great again. well now the front diff wont lock in again and i am manualy pulling the rod and i hear it locking at diff (so i think) and the transfer is locking in just fine but the front tires are not spinning. any ideas?

 

To check the engagement of the front differential, lift the front end of the truck off the ground and safely support it on jack stands. Manually engage the front axle. Spin the passenger side wheel by hand. Does the driver side wheel spin in the opposite direction? Does the driveshaft spin? If neither spin, then the front axle is not actually engaging.

If you have a problem with it slipping out while pushing it hard in 4wd, then the collar and/or passenger side extension axle could be damaged to where they slip when pushed hard. The slipping should be accompanied by a fast clicking noise as the teeth skip over each other.

 

so this morning i put truck on lift and engaged and disengaged the rod to front diff. niether shaft or other tire is spinning. i can hear the rod clicking down at the diff when i pull it in and out and when it is engaged and i spin tire i can feel it threw the cable but still wont spin tire or front shaft. i used the 4wd saturday night and had no problems no clicking or nothing it was great and then sunday i went out and tryd to lock it in and nothing.

 

so i figured out the problem.. the sensor on the diff has a spring and chuck ball. the ball had made a divet on the shaft and it was hanging up so the shaft wouldnt engage all the way. so i took the spring and ball out and works GREAT again. thanks alot for the info swartlkk.