Well I repaired my 4x4 by replacing the rear TC motor, so I tested briefly the 4x4 to make sure it works, and it does, then I put it back to 2HI and leave it like that.

But now, I observe that when I stop at a light, as soon as the truck stop, I hear a soft knocking sound.. Like when you force the shaft to turn on the front TC.. Is it possible that making the 4x4 work, that now the clutch pack in the rear TC are engaging the front TC and making the shaft turn? Somehow I think this didn't happen before, as the shaft was always in the same orientation, but now I know for a fact that it turns always because I can rock the truck back and forth by turning the shaft manually under the truck..

Isn't the shaft supposed to be "free wheeling"? I guess it could be the drag of the clutch pack, but I thought I would break it free easily..

Maybe I'm due for an oil change in the TCs...

 

What year? Blazer/Jimmy or Bravada? 3 button or 4 button transfer case? What "TC motor" did you replace?

 

Blazer LT 2000, NV236 TC, I changed the encoder motor and the TCCM.
The front axle engaged correctly, I can see the vacuum plunger work, retract etc.. Everything works..

Today I could'nt hear the "knocking" so maybe it's nothing, it's probably not important at all, I was just curious to know if somebody else heard that..

The knock I'm talking about is like the sound that the gears do when they take up the lash between them .. Not unlike a motorcycle that you put in gear actually..