A little while back I noticed my left rear tire in the Jeep going flat when I left for work in my daily driver. So when the weekend came I got out my air compressor and filled the tire back up, but when I started to undo the air line I could hear air leaking. As it turns out, my rubber valve stem car cracked. I checked the other three and they too were cracked, but not leaking yet.
I figured there had to be a way to replace the valve stems without having to take the Jeep to a tire store and have all the tires unmounted, new valves installed and everything re-balanced.
I came across this nifty tool, bought it, and it works. I replaced all 4 valves in my driveway. It'd be really great if you tear a valve stem off road. It was about $30, and well worth it. It's pretty simple to use, just screw a new valve into the piece with the red handle and lube the stem, I used Vaseline (hey if it works for...well anyway), but probably many other things could be used, even some motor oil in a pinch, line the cone shaped black piece up to the hole in the wheel, then slam the valve though the cone shaped piece until it goes through the wheel. Then pull the valve back out until it seats in the wheel, then unscrew the tool. You're done. The valve removal tool is a POS and broke on my first attempt to use it, but that was the least of my worries, as the rest of the valve that wouldn't come out of the wheel on 3 of the 4 wheels is just down inside the tire, it makes no noise so I don't care.
This video shows how it works.
I bought it here, if anyone is interested in it.