You can't buy just the pitman shaft but I wouldn't worry about grinding into a few of the grooves. The entire gear box would have to be disassembled to remove that shaft, and that is something you DO NOT want to do. I looked at the web site you listed. The grinder they used is pretty huge for the job. I use an air cutoff tool with a 3" cutting wheel, then I cut a notch straight into the arm 90 degrees to what they showed in their photos. The cut goes into the shaft but doesn't cause any harm. When you get about 90 percent of the way through, the arm will crack open from the stress.
As for the steering wheel being off-center, if you have a 4wd truck, there are two alignment adjustments. One adjusts the left wheel to set the total toe. That one is critical for good tire wear. The adjuster in the link between the pitman arm and right spindle is only for setting the position of the steering wheel. I never had good luck getting a straight wheel with the alignment computer. I always took a 15 mm wrench and the adjusting tool with me on test drives, then I'd stop on the side of the road and crawl underneath to tweak it until the steering wheel was perfectly straight. Part of my problem was there is a lot of play in the gear box when the engine is not running because it needs pressurized power steering fluid to remove that play. It's no fun making those adjustments with the engine running because you're so close to the fan, so even though the steering wheel was locked straight ahead, you couldn't see the tires turn as you made the adjustment.
There are two common causes of steering wander. One is the track bar and one is the gear box. When you replace the track bar you can be pretty sure the steering wheel will no longer be centered. Fortunately you don't need an alignment to get the wheel straight again. Just play with that adjuster to make the wheel straight.
Thursday, February 24th, 2011 AT 1:04 AM