As glyn said, don't know what year or type of vehicle you are talking about, but let me share my experience with my 1953 3604 (3/4T pickup).
Several years ago, I was making a right turn, heard a crack, and discovered my steering wheel was able to spin freely with no control over the direction of travel. Fortunately, I was going pretty slow and drifted onto the shoulder. After cleaning out my pants
I had the truck towed home. Pulling the steering gear box and dissassembling, I discovered that the worm gear on the end of the seering shaft had broken. I found someone nearby with an old truck in their back 40 (literally, in a ditch on the back of their farm). I pulled the steering shaft and then ordered a steering gear box rebuild kit from Jim Carter's. The kit came with a small booklet, a reprint from GM. As doc says, I spread everything out on a workbench, took my time, and in a little over an hour, had the box rebuilt. Definitely one of the easier jobs I've tackled on my truck.
By the way, if you do it yourself, work over a tray (cookie sheet or similar) so that when you drop all of the ball bearings you won't have to spend an extra hour looking for them all
. Don't ask me how I learned this tip
Good luck.
