Ratios between pitman and steering arm lengths...

[Kevin Lee]

What's a decent range and how do you figure the ratio of your steering box and factor that in? The box I have has five and a half turns lock to lock - but I don't know the working angle - if that's a correct term for it. Obviously I don't want to drive a tractor and I don't want arm pump after driving around the block.

[Unkl Ian]

You should have steering stops on the axle.
So with the steering arm bolted to the left front spindle,
you can turn the wheels to full lock in one direction,
and measure from the hole in the steering arm to
a convienient point on the frame.
Then turn the wheels to the opposite lock and measure again.
Subtract the small number from the big number,and let's say the answer is 8".

Now with the wheels straight,turn the box to full lock then back 1/3 turn.
(the box should not reach the end of its travel at full lock)
Measure from the small hole in the pitman arm to the hole in the steering arm.
Then turn the box the other way and repeat.Subtract the small number from the big number.
Lets say the answer is 6".

Now you get to decide if you want a shorter steering arm,or a longer pitman arm,or both.

If you want to make the pitman arm longer,I would tape a Painters Stir Stick(free at Home Depot)
to the pitman arm,mark a few different hole locations,and repeat as above.
When in doubt,make the pitman arm longer,it is easier to make it shorter than longer.

And post pics here of how you did it.

I'd offer to machine the parts for you,
but my boss decided I deserved to have more free time,
away from the daily grind of actually having a job. http://www.jalopyjournal.com/ubbthreads/images/graemlins/mad.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/mad.gif

[C9]

SuperBell steering arms center of two bolt mount to tie rod end center = 5 1/2"

Stock Vega Pitman arm center to center of splined bore and tie rod end bore = 6 1/4"

The Vega steering box is 4 1/2 turns lock to lock.

Steering on my 32 - with my ball bearing column - is easy.
About like a stock unboosted Pinto.
Part of that due to the shorter than stock Pitman arm.
The aftermarket Pitman in my 32 was heated and bent and is now about 5 3/4" center to center.
That does make the steering easier due to the change in the lever arm, but probably not much.
My 31 on 32 rails car with Vega box has an aftermarket Pitman arm and steering with it - rolling around the garage - is very easy.

To my knowledge there is no formula.
Keep in mind the very long Pitmans are going to take more effort in the steering dept.
I'm sure you know as well, a faster ratio steering - like 2 1/2 turns lock to lock is harder to turn as well.

Overall the stock Vega ratio is a good one for the roadsters and I don't feel limited.
Gotta balance quick handling with low speed ease of steering.

[Bruce Lancaster]

I believe steering ratio is computed from degrees of rotation. Put a protractor on wheel and on pitman shaft center, and you can compute box ratio; put a protractor at king pin and you can compute overall ratio.
I think a stock deuce box is around 15:1, pretty quick. Really sluggish rigs like grandmas '75 Buick wagom might be above 25:1, sprint cars down around 8:1. I think Model T's were something like 3:1--sneeze while driving and you're upside down in the opposite ditch.
I don't know what you are doing for pitman and steering arms, but look into making them with several tapered holes like a sprint car. I suspect you could find a pitman thus from a circle track store, and the steering arm could be fabricated from plate.

[Kevin Lee]

Ian - I thought I knew where you were headed in the first paragraph - but the second one has me scratching my head? I have no steering parts on the car right now. The steering arm will be welded up to suit and of course the pitman arm will need to be fabbed as soon as I know for certain how long it needs to be.

Here is my plan and basic thinking behind what I'm doing. I'm starting at the middle and moving out. Longer pitman arm = lower drag link which gives the right steering geometry. Basically everything will be built around the drag link and my main place to adjust steering ratio will be the length of the steering arm. I can measure any point on the pitman arm but I just need some frame of reference for what to do with those measurements once I have them - if you follow me.

[Bruce Lancaster]

If you are fabbing both arms, just drill a row of holes on each and ream with speedway/Ford tie rod taper.
Moving closer to wheel on steering arm will quicken ratio, moving closer to steering box on pitman slows ratio. If you need a flying guess on lengths, it's a fairly safe bet that a draglink box came with an arm not too far from six inches long. Same length steering arm would give you 1:1 ratio in that section of the steering as a starting point. Adjustability here is standard in many types of racer. Too quick is better than too slow on a hot rod.

[Kevin Lee]

Here's what I'm thinking if these sketches make any sense of my ramblings. The top picture is roughly where I am right now - bad news. I don't see this working at all. The bottom picture is where I hope to be. Drag link parallel to the wishbone may not always be ideal but in this case it makes sense. It's all about compromise anyway, right? I think the pitman arm will be a predetermined length - but I will mock up a steering arm with several holes. I'll at least be in the ballpark before I start now. Thanks everyone.

Bruce - this is the GM box you sent. It's going to work perfectly this way but it just wouldn't fit on the rail without notching the engine and head. http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

[Bruce Lancaster]

Looks good to me, and the long arm will make it way too quick, which should be just right for an elderly race car.
Get a couple of dimestore protractors and work out box ratio, then you can figure or mockup with cardboard and coathangers to see what kind of overall ratio you will be getting. I'm thinking from your sketch that you will likely end up with pitman roughly twice as long as steering arm, and that box does need to be quicker...
effort should not be a problem with the ball drive box and a light car. The old holy grail steering for race rods was the Franklin, which was something like 5:1--I think you are going to end up real quick, so put in lots of caster and keep a light touch on that wheel!

[**DONOTDELETE**]

My street-legal will have a short 86" wheelbase. As a result, I'll need fairly quick steering. My Halibrand steering gear is an 8:1 ratio. I did a Cad layout and here are the results. I will use a 7" steering arm on the left front spindle (center of kingpin to center of connecting hole in the steering arm). The wheels will steer 30 degrees left and 30 degrees right. That makes the total horizontal travel of the drag link to be 7" also. I want 1 1/2 turns lock to lock at the steering wheel so, in order to achieve that, I will need a 6.3" pitman arm. 1 1/2 turns of the steering wheel equals 67.5 degrees at the pitman arm (at 8:1 ratio one turn equals 45 degrees therefore 1 1/2 turns equals 67 1/2 degrees total swing). The inverse sine of 33 3/4 degrees (half of the total swing) equals 1.80. 1.80 X 3.5" travel needed for a 7" total travel at draglink equals 6.3" pitman arm length.

Clear as mud ? http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

A car with a longer wheelbase will want a slower steering than 1 1/2 turns lock to lock.

[Tman]

Grim, I think my pitman arm is about 7" long. You are on the right track with the parrallel bone/link. Thats the way I did it. We must have the same damn box as well. Any idea of the year? Mine was pulled when I found it.

[Kevin Lee]

Mine came from Bruce L. It had a shortened collumn and a neat chrome collumn drop. It had been used in a hotrod before. When choprods saw it and told me it was '56 Chevy truck. He told me this with complete certainty and included the other years it came on too but I wasn't paying close enough attention apparently. ('53-'56 maybe?)