There's not enough info. People will only throw guesses at it.
The only way we can help is to either teach you how to diagnose, or get you to do a few checks and report back.
First check is always a the wheel shake with the tires on the ground. Watch for anything that moves. If you dont know how much movement to look for, look at the corresponding part and see how much it moves. If one part moves more then the others, there is a problem.
Watch the distance between the dust sheild and unit bearing. If it varies during the shake test, the bearing is shot.
If all that checks out (which I doubt on a YJ) inspect the tires and rims. Visually inspect the tires for cupping, out of round, or blown belts. All that checks out, do a runout test on the rims, most importantly if they are steel. Dont know what values to look for with a rim runout, do more then 1.
Still dont find anything
Jack the front end off the ground, and check the balljoints. Either a long bar directly under the tire and pry up and down, or hands at 7 and 2 oclock and pry on the tire.
Go through all that and cant find anything, bring it to someone else to take a second look to hopefully find what might have been missed.
Good luck