Thread: Steering geometry issue

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OK, I know we have talked a lot about bump steer, Ackerman angles ect. This isn't about that.
What I am running into is this on my cowl steering. In order to keep the steering box and the axle both on the stops at the same time and keep my tierod anywhere near level, I end up with a steering arm 13 inches long with a 4 inch rise. That is with an 11" long pitman arm. I spent hours scouring threads and doing searches and I can find info on cowl steering pitman arms, info on steering arm issues but no where can I find any one addressing the issue of them both staying in sync to make their respective total arc of travel. I see a lot of foot long pitman arms on some nice cars and they either do not address this issue or have some serious slow steering box.
I can build it strong enough, that isn't the issue.
Here is my mockup.

Why do you want the box to hit the stops? I'd shorten the arm to get the link out from the frame where it'll look better, even if as you say it meant finding a slower box to make it driveable. Arms that long look too Mickey Mouse to me.

Originally Posted by R Pope

Why do you want the box to hit the stops? I'd shorten the arm to get the link out from the frame where it'll look better, even if as you say it meant finding a slower box to make it driveable. Arms that long look too Mickey Mouse to me.

Why?, uhm, because they are supposed to? I mean every car or truck I ever worked on the box hits the end at the same time the spindle does. On a truck with a solid axle you turn it to the lock and adjust the steering stop on the axle to touch, it just seems like the right way to do it. Plus I am concerned with the ratio, if I made them too just look good it would seem I'd have some really twitchy fast steering.
I don't want it to look mickey mouse either but I don't want to compromise function for cosmetics either.

No, it doesn't have to hit the stops. Yes, in factory cars they can engineer it that way, but when we start using one brand box with lots of other mismatched parts we end up with things that don't quite operate that way. On my '27 the steering box still had more turns to make even though the wheels were cranked as far as they could go without hitting the radius rods.

I think that steering arm is way too long, both cosmetically and functionally. None of the ones that are commercially available are nearly that long. I would go to a regular length arm. The 4 inch rise also concerns me, but I understand what you are trying to accomplish with the level draglink and all.

Don

You don't want the steering system to use the internal stops inside the steering box.

Use the axle stop nuts.
You can trim these shorter if needed to gain a sharper turn, but let the stop nuts do the stopping.

Vega boxes - and I'm sure others - will be damaged by using the internal stops.

Fwiw, a stainless Chevy mag lugnut makes a great stop nut.
You'll have to trim it down a touch, but that's easy.
They're 7/16-NF as are the kingpin lock/stop bolt threads.

The Vega box is about 4 1/4 turns lock to lock and the pitman arm is 6" long.
I have a 5" long pitman arm and while some may perceive the steering to be too slow, it's not.
Parking is quite easy as well.

Granted, the Vega is a cross steer setup, but the pitman arm lengths and steering arm lengths could be duplicated on a fore & aft draglink setup like yours without too much trouble.

Keep n mind, you can still make changes after the car is up and running.

OK, so I can live without the box on the stops. It is a 3 1/2 turn box. I do feel like I need to keep my drag link fairly level. I did design the radius arm pivot points to be perpendicular to the pitman end at center. Since the car is a ways away from drivable I think I will just make it look right for now and deal with it all later.

I think that is a wise decision, build it and see how it handles. You may have no problem at all. To be honest, I don't know what the proper way is to align the draglink on a cowl steering setup. Does it have to travel in the same arc as other stuff? Not sure.

Don

The pitman arm on my sprint car is 14 inches long the steering arm at the spindle is 5 inches long and the drag link is 50 inches long. The drag link is no where near level and travels up hill from the pitman arm to the steering arm at the left front wheel with no ill effects. I would think a drag link of that length or the length your gonna need would have very little effect on bump steer or arc. Now if that drag link was only 15 to 20 inches long such as using the old Mustang steering box I would say you had better be sure the drag link is level. Looking at your pictures I would say your gonna need a longer pitman arm and a shorter steering arm at the spindle. you don't wanta use the steering box as a stop,do that at the spindles and please please get rid of that wrench for a steering arm (it looks Skeeery) you gotta remember if that breaks you loose all steering ability.

Yeah, I think that's about right, longer pitman, shorter steering arm. The wrench was only on there as a way of moving things around.
But also remember that on a sprint car you are sawing the wheel about 3/4 turn, lock to lock. I've never driven one but would you even notice if it bump steered?
My permanent steering arm with be made of 1/2" steel rod and be mounted in all 4 holes on the spindle because the econoline spindle holes are just 2 1/2" on center and it's a little tweaky mounted in just 2. I will have the 1/2 inch rod turned down to 7/17 to fit the holes and thread it for nuts. I just don't want to build it until I am sure on the length and rise.

It's more than 3/4 turn but I can't check it cuzz its on the trailer and can't get the whhels to turn far enough. Never felt any bump steer although your usually wheeling it hard nuff ya might not notice. But I have ran Duqoiun & Springfield miles in a midget with virtually the same setup and never noticed any bump steer other than those little cars are real real twitchy goin that fast.

[QUOTE=HWORRELLBut I have ran Duqoiun & Springfield miles in a midget with virtually the same setup and never noticed any bump steer other than those little cars are real real twitchy goin that fast.[/QUOTE]

Never have run either of them, but it's gotta be a blast in a midget!!!! I did do a few laps on the mile at Syracuse in a sprinter!!!!!!

I am using an Econoline front axle on my track roadster and a Ford Ranger steering box (with an extension on the sector shaft) mounted in the cowl. I am using the stock Econoline steering arm on the spindle (for setup purposes) and a GM Metric pittman arm on the box. The ratio seems about right from past experience. I hope that helps for giving you an idea of arm lengths...

As for bump-steer.., almost all parallel steered cars have some bump-steer unless it is a very carefully designed four-bar system. Cowl-steering setups are the most likely to have bump-steer. In order to eliminate bump-steer, you would need for the rear pivot point of the drag link and the rear pivot point of the radius rod to be in the same place (as viewed from the side) so they move in the same arc. Unless bump-steer is drastic, don't concern yourself too much about it. You will get used to the way this car handles and it will become second nature to automatically correct for bump-steer as you drive. In the C-Cab below, I had the radius rods mounted below the frame rail, of course, but the drag link was about 6 inches above the frame. It handled fine and had very little bump-steer.

Here is my 2 cents worth. Ideally what you want is a parallelogram, so there is no bump steer, not always possible. But small compromises are very forgiving. You can adjust to them. It's not good to use your steering box as the stops for steering. I would choose a correctly built steering system than quick or slow steering radius. With a slow turning radius just turn your steering wheel until it hits the stops and light those hides up, it will turn really sharp
Ken

Ah, yes, the old throttle steer, why I never liked fwd cars.
I guess I never really considered the steering box the stops, I just wanted to be using the full stroke, which apparently isn't the issue I thought it was.
Now I am trying to remember how the Saginaw power steering pressure relief works. Is it just a bypass in the pump or does the box bypass at the ends of the stroke

Today I wanted it to steer, just to see where I need to go next. I went with a foot long pitman arm and shortened the steering arm back to 10 inches and left the 4 inch rise, that was about as far as I felt I wanted to compromise out and still keep my drag link level. That left me with about 2 turns stop to stop and everything is tweaky. 10 and 4 are just way past acceptable and the econoline spindles are too small to really get anything very stout bolted to. What I thought was a stout and well braced steering box isn't. It seems like a big bucket full of compromises no matter how I cut it at this point. Tomorrow I am going to try and scrounge up an econoline steering box and start over I think.