So I have a 2000 blazer LS 4dr 4wd. I wondering what exactly could go wrong with the front differential that controls the 4wd? I had my local shop replace/rebuild my front diff with used parts last year, they grab one from a u pull it place and kinda frankensteined working parts together. I was told it’s as good as new but it’s been about a year and 4wd stopped working again. The 4wd activates and it clearly clunks into 4lo but I have no resistance when turning and the front wheel spin freely when in 4wd

just looking for any help I can get as last time they charged me over $1600 to fix my 4wd (sounded obscure to me but was kinda in a pickle and need my 4wd done)

 

Sounds like the actuator isn't engaging the front axle.

 

The front axle engagement is controlled by vacuum. Sounds like a problem with the vacuum switch on the transfer case, the actuator under the battery tray, or the related hoses.

 

actuator is good and fully pulling cable

 

It also seems as though the gearing does change when in 4Lo because of how the torque of the rear wheels feels, but again no movement in front wheels. I don’t know it this will help but figured it should be noted.