The relatively short telescoping shaft with a U joint on both ends will have a bad habit of binding at certain angles, particularly if oddball terrain is encountered. The movement of the axle, the springs, and maybe a little frame flex added in can cause the steering column shaft to get into an angular bind sufficient to lock the steering wheel at a deadly dangerous moment. Since the rack and axle move as a unit, bump steer won't be a problem, but the geometry of the telescoping shaft will be unpredictable and dangerous.
If set up correctly to account for the range of angles and distance of telescoping action of operation, there is no reason why the shaft would not be totally reliable and safe. If done poorly, yes, it certainly could be unpredictable and dangerous.
BTW, I have run telescoping PTO shafts on my farm equipment for 30-something years, and your argument comparing them to a steering column shaft is totally bogus. There is virtually no comparison since the operating angles are very shallow on PTO equipment and the shaft length is many times what a steering pinion shaft would be.
Jerry
I disagree. Agricultural drivelines operate at constantly changing (going over terrain much similar to what the truck suspension would encounter) and at times near the limits of their angles of operation (while turning corners).
The length of the steering shaft is not relevant as long as the shaft is of sufficient length to travel freely over the minimum and maximum possible telescopic lengths without bottoming out...and the U-joints are correctly placed and have the capacity to handle the range of angles required. Again, poor design would produce disaster. Good design would be totally workable.
Please don't misunderstand, I am NOT promoting the use of rack and pinion on a straight axle, NOR am I going to use it on my truck. I find it an interesting subject and am interested in what others think and WHY. A lot of people seem to say "this is dangerous" or "that is dangerous" without being able to discuss the WHY...so I appreciate others who are will to offer their thoughts on the subject.
