Is it easy to replace the knuckle on front driver's side and how much should one cost?
Junkyard diving would get a replacement for under $100.
I think it would be easy.
To get one off:
Take the hubcap off, loosen axle nut, crack lugnuts, jack truck up, get on jackstands, remove front tire, remove brake caliper bracket, hang caliper by wire-do not let it hang by the hose, remove rotor, remove upper balljoint pinch bolt and remove the balljoint from the knuckle (you might need a punch or drift for this), loosen the castle nut on the outer tierod and the castle nut on the lower balljoint (on lower loosen to the point where it almost comes off), remove axle nut, remove castle nut on tierod-remove tierod from knuckle, you should be able to remove the CV axle from knuckle, then get under truck with long screwdriver and pry between the inner flange on the CV and the front axle assembly-it should pop right out, strike knuckle where lower balljoint goes thru with a BFH-hit it good and hard, it will drop down to the castle nut, remove castle nut and knuckle. Congratulations, you just removed your 4X4 steering knuckle. Remove your wheelhub/bearing from old knuckle, install on replacement, then......
Replacement is reverse of removal, should take the novice about 2 hours.
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EDIT: you can also go by the "how to replace your CV on a second gen explorer" just take it one step further by replacing the knuckle. The link is to a "sticky" in this section, with pics and all.
http://www.explorerforum.com/forums/showthread.php?t=187964&page=2
