Everything seems good inside ****pit.
The 4x4 engages with a stiff action
as always. The 4x4 light comes on the dash.
However no front wheels spinning.

Put on lift and verified no front wheels engaging.
I checked the large vacuum modulator, linkage had
a bit of rust/ mUsed P Blast and moved the lever IN
amd the front wheels spun together. Pushed
the lever out and front wheels spun independently.

Is the modulator bad or did I loose vacuum?

How can I troubleshoot?

Thanks for any help, I have no manuals.

George