If you aren't going to add power steering, forget the rack and pinion gear. I personally don't like rack and pinion steering, and I wouldn't go to the trouble and expense of converting a good worm-and-sector gear in anything, let alone one in a large truck. I know all the arguments in favor of rack and pinion steering, but underneath it all, the advantages are mostly on the side of the manufacturer, for saving in both cost and weight. As far as a mechanical advantage, you can get the same quick steering response in a worm-and-sector gear by using a longer Pitman arm and smaller steering wheel- like the early Corvettes. Then add power steering if there is any weight to the vehicle at all. Or get your daily work-out trying to steer the thing.
If you go to rack and pinion, you usually have to increase positive caster (I think) on the front wheels, to aid in returning the wheels to straight ahead after a turn. The increased caster causes higher turning effort, which is one reason you rarely see a vehicle with rack and pinion steering without power steering. Also, rack and pinion gears tend not to straighten from a lock position- you have to turn the steering wheel from that position. A worm-and-sector gear tends to return to straight from the lock without steering wheel assistance.
My opinion on the matter-- keep the worm gear.
Harvester
