This is a typical 'While you are in there' situation.
I suggest to prepare for replacing the steering knuckle bearings and the axle shaft bearing / bronze bushing, too. You should also consider replacing the wheel studs. Also a closer look at the steering rod ends is adviced. And you should also do the oil seal / felt on the chrome ball."
This was originally my comment.
Those items (except wheel studs, those sit in the rotors flange) require removing the knuckles (What I called 'going 'beyond the spindle'). I'd only do that, if serious wear is suspected or obvious. If not, just fix the rotors and don't touch the knuckles.
Here is how to judge things:
Tierod ends can be inspected from outside.
- Check the rubber of the ball joints in the steering gear for cracks or holes. If the rubber is cracked, hard or torn, the joint needs to be replaced.
- With the wheels on the ground, move the steering and observe the ball joints in the steering gear for any play. No play: Nothing needs to be done. If there is play, options to fix it depend on where the play is: The links may be adjustable (it's the case if there is a cotterpin across the end). The ball joints on the knuckle steering arm can't be adjusted; if those have play, replacing those is adviced.
- Some joints are greasable. If you have those, greasing them should be part of your service routine.
The knuckle bearings sit top and bottom of the knuckle and allow it to pivot. Those may need adjustment or replacement if there is excessive play (or if you need to go into the knuckle anyways). Severe play in those bearings leads to squashy or steering and uneven tyre wear. Play and wear of those is hard to diagnose, though. You mainly do those bearings as preventive maintenance once you digg into the knuckles anyway for a full rebuild. ('While you are in there anyways').
If the oilseal in the axle is shot, diff oil makes it into the knuckle and eventually a messy mixture of grease and oil seeps out at the chrome ball felt seal.
A shot axle seal requires a full knuckle job to get fixed.
A healthy knuckle has a light coat of grease on the chrome ball, but no big oily mess there.
They shouldn't be bone dry either...
There should be Moly grease in the knuckle. There is a 1/2 inch square plug on the top of the knuckle to check / top up grease. Should be part of the service routine.
Chrome ball with grease on the bottom and dry further up indicates not enough grease in the knuckle.
You may post pics of the chromeballs here and we'll see.
The bronce bushing / needle bearing sits in the spindle and guides the drive shaft from the CV joint. It gets greased from the above mentioned grease in the knuckle.
If it's worn, there mostly will be vibrations in the front driveline at higher speeds, when 4x4 is engaged.
If the chrome balls look healthy/ no oily mess, and if there is no permanent servicing issue (lack of knuckle grease) suspected, and if the 4x4 in front works without vibrations, I wouldn't go beyond the spindle and do the rotors only.
(I hope you can trust your mechanic in his diagnose)
Good Luck Ralf
