1988 Jimmy

i have a 1988 jimmy and it won't engage 4 wheel drive. the shaft will spin but won't turn the wheels. I hear a loud ticking noise. Can someone help?

Sounds like the hub is not fully engaging. My be stuck, old grease maybe. I would try pulling the hub apart and cleaning it put in new grease and then try it.

The front hubs are splined and they are always engaged on GM T series vehicles. There is a clutch mechanism on the right axle shaft that engages / disengages the axle from the front differential. When the engine is running, and 4WD is selected, there should be manifold vacuum applied to the actuator. When 2WD is selected, vacuum is vented to atmosphere and the cable retracts. The actuator is located under the battery tray. Make sure the diaphragm is not torn and that it holds vacuum when applied.