Ok icy roads this morning so I figure I'll try out the 4wd and it vibrates bad. I unlock the hubs and leave the tcase in 4 hi and no vibration. So I'm thinking wheel bearings. What do you think?

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99 ford ranger xlt stepside 4.0l 4x4 auto.

More than likley its one of the three front axel U joints, cause wheel bearings turn anytime you're moving, so if no vibration with hubs locked out they wouldn't just do it with hubs locked in. It also could be one of the U joints in the front drive shaft.

well no vibration anymore. changed the wheel bearings out in the front and no vibrations.

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99 ford ranger xlt stepside 4.0l 4x4 auto.