Technical Is my setup strong enough? Cowl Steering Question

I think everything got lost in translation, He asked about the pitman arm not the good and bad of bump steer or cowl steering Lloyd, just stop!

 

Oh, your Chevy comes with the bump steer option already. Along with a good bit of Ackerman error.

 

I figured the OP got his answer regarding the pitman arm (an overwhelming TOSS IT IN THE CAN) a long time ago and the conversation moved on from there. Pretty sure this isn't the first post in the history of this site to go sideways
I am more than happy to express sadness for my part in the derailing ... I have a lot of work to do before I will be allowed out in public, please bear with me, it is a long and tiring journey

Please accept my sincere apologies

 

It's not exaggerated. 2.5" up and 2.5" down at the spindle.

 

So now we are sideways, and now I am debating the way forward. I dont have much clearance between the 5" channel and the headers.

So the three options I can see that might fit are
1) keep the side steering design, but will have to cut out part of the fully boxed frame, may have issues with clearance. F1 box? I like it would look more traditional, and the lease redesign of the existing setup.

2) vega box, less intrusive frame mods, looks like easier steering shaft route, have to add a panhard rod with cross steer.

3) uni-steer "half rack" kit. Most room, shaft similar to vega box, least traditional looking but likly drive the best. Also require panhard rod, and new steering spindle mount.
https://www.unisteer.com/products/1928-32-ford-cross-steer®-retro-fit-w-no-mounting-holes-in-bracket

Open for ideas, pictures a plus.

 

The top of the pitman arm that tensions the collar looks brazed on, and has some pits/imperfections in it when you look at the closeup. It's highly questionable not only from a materials perspective, but also the transfer of all of that force through a single keyway. Every cowl steering setup I've seen uses a splined shaft attached the corresponding pitman arm, transferring that force around the whole shaft, not just concentrating the load in one spot.

Most of the Hilton cars are cowl steering, and are driven all over the country without issue. I'm pretty sure they use a Schroeder box of some variety. I'm sure someone here can elaborate. But they seem to have a solid formula in terms of parts selection and chassis setup that is both safe and reliable.

 

Those and the Rolling Bones cars are probably some of the hardest driven hot rods on the roads today.

 

Here again, "at the spindle" is describing something oppo of what they are showing which is at the perch pin. Plus, your typical Shorty hot rod shock used on the front only has roughly 3" of stroke

 

Don't forget option #4. Re-engineer what you've got with a stronger pitman arm.

 

That would imply it was "engineered" the first time...

 

I have had 2 Vega boxes, then a Unisteer in my Model T. The frame was built to model A dimensions. Both vega boxes wore out quickly. Junk boxes from Speedway. Too slow of steering for my tastes. Like 4+ turns lock to lock. Big turning radius. And too much effort for my bad shoulder.
I put a Unisteer in. A little quicker, but still slow. More precise. Still a very large turning radius. About the same effort.
I needed power steering. I bought a CPP 400 power steering unit. Bolts right in place of a Vega box. 12.8:1 ratio. Low effort. Turning radius is a lot tighter. Steers like a new modern car. I will admit that getting the power steering pump in there stretched that 5 pound bag to the limit.

 

I wouldn't trust the 'spacers' on the drag link arms either. On the top arm too. Just because you can do things to join A to B, doesn't make it a good idea.

 

Not to beat a dead horse, I think you're already set to redesign the steering, but after seeing this larger view photo this only emphasizes the need to redo things. The added scrub radius on that front end with the finned drums and offset wheels will add even more leverage against that pitman arm. So yeah, time to rethink things.

I'm a fan of side steering for a couple of reasons, first it just seems more traditional looking to me. Beyond that, if you go with a Vega box and cross steering you should add a panhard bar up front, or a dead (or deadman) perch, because the cross steer setup is going to put sideway forces on the axle that are not there with side steering. Location of the box can be a puzzle. The W engine doesn't leave a lot of room to work with.

You could retain the cowl steering, acknowledging the potential for bump steer, but the problem you have besides the pitman arm is the non-splined pitman shaft. That smooth keyed shaft has got to go.

Something that might help you locate the box, whether side steer of cross steer, is the Steer Clear steering box drop.

https://www.speedwaymotors.com/Steer-Clear-Steering-Box-Drop-Brushed-Finish,6254.html

 

The heck with the steering……..do I see a ‘W’ motor valve cover???

 

GME Nields Mfg Power Steering Gearhttp://www.gmemfg.com › remansteerings

 

You do, 348 out of a 61 impala.

 

That's badass

 

Go is no problem, stopping is great, I just need to teach it to turn!

 

It's really, REALLY pretty, but, you know it isn't right. The appeal of the polished brass I get. It's jewelry, it's sculpture, it's different, but that isn't up to the task you're asking it to take on. I've not built a car with cowl steering, haven't driven one, and I get that it's going to be a major project to change the set up you have, but there has to be a better way to point the car where you want it to go.

 

should use a steel plate and angle inside cowel from frame upto mopar box. bolt box to frame. outside cover is mostly for show- not a solid base for box.Agree with above- don't use brass for steering arm- look at sprint car arms. Keep angle of arm to steering rod Close to 90% angle on both ends. With inside plate it will not flex. Take your time

 

Precisely. A lot of opinions about the suitability of brass for this component, and not a single attempt to determine how strong it needs to be. Hoe strong does it need to be?

The steering system is a chain of components from the front wheels to the driver's hands. Ultimately the source of load on the chain is going to be the driver's hands. How much weight could you lift by turning the steering wheel clockwise, if the weight were attached to the wheel at the 9-o'clock position? 50lbs maybe? I'm thinking I'd struggle with that, but let's say 50lbs.

Assuming a 16" steering wheel, that's 33lb.ft on the steering column.
Assuming a 13:1 steering box, that's 433lb.ft on the pitman shaft.

We might have impact loads on the front wheels, so let's double that: 867lb.ft
We're not quite sure about the quality of the brass, so let's add 20% for safety: 1040lb.ft

It sounds a lot in engine peak torque terms, but as bending moments go it isn't anything extreme. Will that brass arm survive 1040lb.ft? I'm not going to try to calculate the strength of that part; I don't have enough information. What I can do quite easily is calculate the cross-sectional dimensions of a solid rectangular bar which will survive 1040lb.ft.

The first surprise in that exercise is looking up tensile strength for typical brasses and finding that they are only slightly weaker than typical mild steels: so to everyone who said that brass won't be up to the job of a mild steel part, you're probably at best less right than you though you were. Of course neither brass nor mild steel would match a steel forging. And as to the possibility that it might be a brass-plated part, I know brass plating when I see it, and I don't think I'm looking at it now — which is good because, had it been brass-plated, chances are that the substrate would have been zinc alloy, which is little more than half as strong.

As to the size: working on a median tensile strength value, we'd need an arm of 1.335" square, or alternatively 1.542" deep x 1" thick. The OP's photo with the tape measure is on the face of it pretty much in that ball park. Given that I've been working on fairly generous assumptions it'll probably be OK — but don't sue me if it isn't.

As for the steering geometry, suffice it to say the OP has been warned.

 

Using a reversed Corvair unit with an old truck arm on my 34 Coudan. NO problems, it was a bit slow, so redrilled the arm off the spindle by about 1 inch. Works for me and about a forth the cost of Shroeder.

 

My Chris Craft (1954 17' Deluxe Utility) has a steering arm that looks very much like that, and, it's bronze, not brass. The loads on that have to be pretty close to the load imposed on a steering arm for a car (at least the abuse my boat suffers leads me to think that), I think my concern is more the single clamp, and the fact that steering in a boat isn't as precise as a car. A little play in that arm against the square shaft with a sloppy single keyway isn't gonna make any difference in a marine application. That's my concern. And the geometry.

 

Great technical post as usual Ned. I'm bothered more about how the arm is mounted and secured to the shaft than I am about the strength of the body of the arm. I really wouldn't want to trust that keyed mount with those tabs to a 1000#" shock load, that's sketchy in my book.

 

1018 mild steel 1/4" square key stock yield strength +- 50000 psi quick internet search ...

 

You do realize they do just that on open wheel oval track race cars?

 

Ned, outstanding post. Wouldn't it be pertinent to the analysis that even if the brass arm itself could survive the forces exerted upon it, that the concentration of forces on the keyway and where the keyway meets the arm could cause a failure? A splined attachment of the arm to shaft transfers the forces 360 degrees around the shaft. Whereas the keyed stock concentrates all of those forces in a single spot.

 

Indeed. Road bumps are transferred directly to the Pitman arm, whereupon the Pitman arm amplifies the force and applies it to the key. That means a brass keyway is going to take a lot of bump cycles from a steel key. I'd go with a splined shaft and a beefier Pitman arm if I were determined to keep the cowl steering.

 

IMHO That brass pitman arm is many many multiples weaker and also more brittle than the Ford forged steel arms, with tapered splines shaft, held on with a giant steel nut and lock washer. I would sell that to a boat guy and pick up any decent automotive (Ford, Saginaw, Mopar, Ross) unit that will fit your setup. Safety first! Good luck

 

And yes, I know it was your animation