1990 Full size Blazer
350 engine
Automatic trans

Had this Blazer about 9 months now and never needed to put it into 4 wheel drive until now. I put the truck in neutral and put the lever in 4H then I put it into drive and the front wheels wont spin.

I assumed it had auto locking hubs because there is nothing to turn at the wheels, (see photo).

No problem did a online search and everything I looked up said it was the actuator 9 out of 10 times so I ordered a new one and it came in. I go to put it in and there is not one on the front axle or even a spot to put one. There is not even a cable to engage it off a vacuum source.

I found a vacuum pump next to the master cylinder (see photo) in the corner under the hood with nothing attached to it. I think it was for the cruise control? Other than that I see no other obvious thing that will get it into 4 wheel drive.

I included a pix of my front differential. There is a hose coming out the top of the front pumpkin that is fastened to the drivers side radiator support with a plug or small filter at the end of it and I am assuming it is a vent line.

Any help will be appreciated.

 

Those are auto locking hubs and they are likely frozen up. I would recommend replacing them with a set of selectable lockout hubs like the .

The actuator you purchased is for the NBS trucks with the independent front suspension setup, not the older squares with the solid front axle.

 

If the hubs are automatic, what determines this? Is there a sensor or some thing?

 

Its like a one way clutch , when you engage the 4x4 lever the trucks forward movement locks the hubs , when you select 2wd you often have to back up to unlock the front hubs.