The Stovebolt Site Forums The Shop Area General Truck Talk Rack & Pinion / Straight Axle

I just got off the phone with No Limit Engineering and they said they have a kit that will let me put R&P on my straight axle truck. They said there was an article in the Jan. issue of TRUCKIN' Magazine. I went to their web site, but it was not on it. Now I have been lead to believe that R&P on a straight axle was almost impossible. (I mean, I knew a guy who DID have it, but he used the old Pinto "cable" shaft to connect the steering column to the rack and pinion. It never looked safe, but he drove it a LONG time. Ford discontinued the pinto shaft for safety reasons, at least that's what Ive been told). Anyway, what to you guys & gals think? Thanks in Advance.

I think it would be nearly impossible to put a rack and pinion on a straight axle. I can't concieve of a way to avoid bump steer if its mounted on the frame, and how would you connect the column if its mounted on the axle.

Axle mounting the rack seems the easiest way to avoid bump steer. But once you solve the steering column issue you've now added 50 to 100 pounds to your unsprung weight, which means your handling and ride have been hurt.

I don't think its a good idea. If No Limit has overcome the issues I'd love to see how they did it.

OldSub,
Me too! They finally got it on their web site: http://www.nolimit.net/index.asp?PageAction=Custom&ID=61
I haven't found the article in Truckin' Magazine that No Limit referenced. The magazine is a Primedia publication. I have heard that Rob Fortier frequents this site. If this is true, do you think he would tell us the truth about this setup?

Looking at the picture did not increase my confidence it would be a satisfactory arrangement.

Fortier does show up here from time to time and I've seen him on other boards also. I haven't liked some of his answers about the direction of the magazine but I think he has been honest and answers with integrity.

That picture did leave a little to be desired.
I read Classic Trucks also. I have mixed feelings about the direction the magazine is taking too. On the one hand, I think a truck is only a classic if you can unbolt the rear fenders. On the other hand, who am I to tell other people what to drive or like. They all look pretty good to me.
That being said, Fortier has said on more than one occasion in the magazine about the "STUFF" he puts on his truck had best be able to take the rigors of the road if it is going to be his daily driver.
I am glad he has been honest and does answer with integrity. It was not my intention to malign Mr. Fortier and if he read this and took offense, I apologize.

A rack mounted to a axle is more common than you would think and actually works pretty good. No chance of bump steer with the rack mounted to the axle as they always stay in the same relationship to each other. The key is using a u-joint and splined slip shaft that allows the steering shaft to expand and contract slightly as the axle moves up and down as the suspension works. I have a few friends that have run racks on axles for years and I haven't heard any complaints other than that they don't like the looks of the rack hanging off the back of the axle.

But you've added all the weight of the rack and pinion to the axle as unsprung weight. Ride and handling will both suffer. I don't think the trade-off would be worth it.

Rack and pinion steering is nice, but so are ride and handling.

Ride and handling on a 49 straight axle, thats a good one, besides that an aluminum rack probably weighs less than the old tie rod assembly

I noticed that the article said that it provided new steering arms to "reduce bump steer". I wonder if they are admiting to adding some with their setup.

Last year Classic Trucks or CustomCT had an article on brake systems and there were some technical mistakes in the article.

Oldsub,

I am not sure I follow your thoughts on unsprung weight and its effect on handling.

In this application, unsprung weight would be a load not supported by the springs, or unsprung. The steering rack is attached to the axle the same as the wheels/tires, spindles and brakes.

How would a small addition of unsprung weight effect the handling of a rig...it would be like putting cast iron hubcaps on, it doesn't seem like the ride would be effected.

Was I asleep in Suspensions 101 (probably).

Too-sprung-Stuart

Stuart unsprung weight is exactly what you say, weight that is not supported by the springs.

Big wheels and tires, and big brakes, can also add unsprung weight.

The more unsprung weight the less the suspension will be able to control the movement of the tires. The more unsprung weight the more each bump might bounce a tire away from the pavement, and decrease the amount of control that tire can offer.

Its probably as much engineering 101 as suspension, because most of this issue is the impact of the added weight on moment arm calculations.

The weight of a rack and pinion is not likely to be huge and neither is the impact on ride and handling. But given the limited advantages of rack and pinion steering I would not sacrifice any of the ride or handling capabilities to achive it. I'm not willing to believe the benefits would exceed the negative impact on ride and handling.

And I sure won't be paying that much money for suspension changes that degrade handling. If any of you try it I'd like to hear about how it drives once you're done.

All of that said, I should fess up and say that I've been thinking about converting the IFS clip I plan to put under one of my projects to rack and pinion.

I like rack and pinion, I don't like unsprung weight.

:confused: I am confused. If there is only the one u-joint at the R&P, would'nt that cause some kind of stress above the slip shaft as the front end went up & down? Is it implied that there are two (2) u-joints (one above the splined slip shaft and the other at the R&P)? And what about the left and right movement of the axle (in a curve)? I am sure I am missing other factors. Like what occurs when you are braking hard, in a curve, AND hitting a bump in the road all at the same time?
truckernix : Have you read the article about the No Limit R&P conversion? What were the technical mistakes in the braking article?
Thanks in advance!

Oldsub,

Thanks for the great explanation. It appears I was asleep in class...probably had a sprungover.


Stuart

Its not unusual for a magazine article to have errors, either because the writer didn't know what they were talking about, or because an editor took words out or otherwise changed the meaning of something. And sometimes experts will actually disagree...

I don't recall the article truckernix is referring to, but have no doubt errors occured. It's usually a good idea to check several sources on subjects like these.

I haven't read the rack and pinion conversion article, but I'm sure they are using u-joints on both sides of the slip joint to make this work. When calculating the added weight at least some of the steering shaft will be weighing on the front axle also in this arrangement.