I read some prior discussions here on the stovebolt forum before posting this yesterday. It seems many jump in and predict a horrible death from R&P on a straight axle, but the reasons why are not discussed. I would like to understand the "why".
So far, there have been three negative items mentioned...
1) He saw one on a truck that was done "Mickey Mouse". I have seen some IFS jobs on vintage trucks that could be described the same way. Do it right or don't do it.
OK, you do have a point there. The truck I saw was definitely done with an aftermarket kit. Even then, the whole thing looked very shakey to me at best.
2) "questionable steering column that has to telescope and flex with the suspension" To me, this is the major drawback to R&P on a straight axle. The rack has to be mounted on the axle for it to work, so the steering shaft has to be able to move with the axle. But it's not something that I feel cannot be worked out to be reliable and safe. There are drivelines on all sorts of agricultural equipment that telescope and flex while running at 540rpm all day every day...as long as it is kept greased.
Big difference between a driveshaft and a steering shaft. Loose the driveshaft, you only loose power to whatever is being driven. Loose a steering shaft, you loose all directional control. Also, a beam axle not only flexes up and down, but there is also some side to side motion. Having the steering gear mounted to the axle rather than solid to the frame will lead to bump steer issues because of that flex.
3) "add unsprung weight to the axle" So you remove the tie rod and add a rack. Considering the total weight of tires, rims, rotors, calipers, axle...is the net increase in unsprung weight really that much?
The weight of the brakes, tires, wheels, and axle are all figured in when the suspension was originally designed. The tie rod on these trucks maybe weighs a few pounds. A typical rack and pinion weighs somewhere around 50-80 pounds, depending on whether it is power assist or not. Adding that much weight to the axle as unsprung weight will affect the handling and ride, that's why none of the oem manufacturers mount the steering gear that way, that does apply to larger wheels/tires, heavier brakes, etc.
I am curious what others thing about this. Please jump in.
Tim
