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 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.

I know this thread is old and I haven't posted for a while. I had put this whole thing on the back burner for a couple years. I just this week got it all ironed out. It took some doing and not quite traditional to say the least.
There was just no way to get what I wanted with the pitman shaft coming out that high on the cowl so I built this drop.



It also slowed down the steering as the sprockets are 11/15. Then I had to extend the steering arm because the tire hit the drag link in a left turn.
Here is what I had.


And the modified version tacked in place.



My drag link is level and I now have full swing on the steering wheel with a little over 3 turns and both spindles hitting the stops, plus I didn't give up any footroom.

Wait!! Before you spend money on another steering box, take some measurements on what you have. You can use virtually any steering box and it will not make any difference if the proportion (ratio) of the arms is too far off...

On my roadster I measured the steering arm (on the left front spindle) and the Pittman arm. The steering arm (stock arm on the Econoline axle), from the center of the king pin to the center of the drag link bolt hole, is 4 1/2 inches. The Pittman arm I am using is 7 inches from the center of the steering box shaft to the center of the draglink bolt hole. That makes the ratio between them of 1.555 to 1. My steering is 3 turns lock-to-lock. This is a very light car, but that's still a little quick.

On my coupe, which is cross-steered, I am using a 1962 Jeep axle and a mid-80's Toyota 4WD steering box. In that application I am using the stock Jeep steering arms on the spindles, the stock Toyota Pittman arm on the box, and a Speedway Motors "piggyback" tie rod end to connect the drag link to the tie rod. The steering arm is 6 5/8 inches and the Pittman arm is 5 inches for a ratio of 1.325 to 1. This gives the steering 4 1/2 turns lock-to-lock. The coupe is heavier than the roadster and has more weight on the front wheels, so it needs the slower ratio.

When I make the new steering arm for the roadster, I will lengthen it slightly and I will also make it come up a little higher to take some of the rise out of the drag link...

I hope some of this helps; I know steering setups can be baffling sometimes. If we weren't so far apart, I'd drop by and try to help out...

Thanks J.
I did fiddle with it a bit more today. I shortened the steering arm and lowered it. The angle isn't too bad, now I have about 7 1/2" steering arm measured from the back of the spindle plate. I only have about 1 1/2 turns lock to lock now. There is still a lot of loose stuff to deal with.