I have a 99 ranger 4.0, 4x4, dont know whats wrong with the 4x4. I put it into 4 hi or 4 low i hear it shift but the front tires do no spin only the rears do. The front driveshaft spins and so do the front axles, but the tires dont, i dont know if its just the auto locking hubs (one is about 4 months old) or something else? it was working fine before i had the wheel bearings replaced. does anybody know what might be wrong?

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1999 ranger 4x4 supercab, 4.0L
-3 inch PA body lift
-16 inch pro comp alloys
-33x11.50 BFG all terrain
-Go Rihno roll bar with 4 KC Daylighter lights
-weston bull bar
-dual exhaust,
-air box mod, tightend throttle cable.