Picked up my new xB sans hubcaps and noticed the front spindle threads had a coating of rust on them. Probably sat in Portland for a month in the rain. These are normally covered by a grease cap on most cars. I was told xB does not use caps and the wheel bearings are non-serviceable. I had them put a thin coating of wheel bearing grease on the threads before the caps went on. In the tech .pdf it says do not grease the threads of the nut that goes on this spindle. Did I screw something up? Should I wash the grease off and coat the threads w/ POR 15 to cut down on the rust. That wheel will have to come off eventually for disc turning so I don't want the thing a frozen rusted mess. Better yet, is there a grease cap available to keep the elements off the spindle threads?
You are OK. Generally front wheel drive cars don't have dust covers over where the outer wheel bearing would be. Applying grease on the threads after the nut is installed and torqued is fine. Most torque specs are for nuts and bolts that are clean and dry, no oil, grease, or Lock-tite applied. If you applied grease to the treads and then torqued them they would be tighter then they should be.
al74dart is absolutely correct - Do not grease those threads before installing the spindle nuts unless directed to do so by the tech. maunals. Protecting the exposed nut & threads after torquing them is won't hurt anything.
I am an aerospace fastener engineer by trade and I have investigated many fastener and equipment failures caused by this very thing.
In basic terms........
Lubricating a nut or bolt will reduce the friction in the threads and the bearing surfaces they make contact with. This reduction in friction will cause more of the applied torque to but turned into higher joint preload (or bolt tension) than the assembly is designed to take. Depending on the spindle/bearing design, lubing the spindle threads could cause damage (by crushing) the spindle bearing when torqued to "dry specs." I have seen many cases of airframe joint failures where lubing the bolts/nuts reduced friction so much that the bolt failed in tension before reaching the specified assembly torque! It's a dangerous combination if not taken into consideration when the torque specs. are established.
Another idea for corrosion protection I use if your worried about it would is to shoot a little Rustoleum Red primer over the exposed spindle thread & nut after torquing it up - Then pop on the hubcaps and your good.
I discovered the rust when switching from my snow rims to my summer rims a couple weeks ago. I just hit the exposed threads with a light coat of hi-temp brake grease I had on hand -- I hate rust ! As mentioned above, pulling the discs shouldn't affect your spindle nut -- that's a bearing consideration.