99 jimmy 4x4 not engaging

when i push the 4hi button I hear the noise that sounds like it's engaging but the front wheels don't engage, same with the 4lo ????? any help would be greatly appreciated guys!!

Under the battery is a vacuum actuator that operates a clutch mechanism on the front axle housing that engages the right front axle shaft with the front differential. With the engine at idle, when you select 4WD there should be vacuum to the actuator and it should pull the cable in about 3/4". Post your results.

cable did not move at all