As many of you know, I am doing a project on a '55 1st Edition AD truck, called "SLURP" (Simple Lightweight Unpretentious Retro Pickup).
In adapting our steering to the new engine's wider physical presence, we have found a smaller high quality replacement steering box, but because its dimensions differ from the stock steering box in many ways, we need a custom Pitman arm to connect from the output of the steering box to the factory drag link on the '55 1st Edition truck.
As many of you know, the '55 1st Edition has a different drag link and Pitman arm than the earlier AD models. The earlier model drag link has a "ball receptacle" for a ball end on the Pitman arm. The '55 1st Edition has something that is more like a tie rod end in appearance. The end of the Pitman arm that connects to the drag link has a simple tapered hole that I have measured and recorded dimensions for.
I have found a company that makes chassis parts including Pitman arms, and they say they can either provide an existing model Pitman arm (if one exists close to what I need), or they can make a fully custom one for a VERY reasonable price.
My problem is that I know nothing about steering system types and measurements, so don't know how to describe the END that I need at the top end of the custom Pitman arm.
I need someone knowledgeable here to tell me what to ask the supplier to build.
I know the center to center length I need, and also have the tapered hole dimensions for the BOTTOM hole in the Pitman arm. But, I need to be able to describe the "splined" hole at the top of the Pitman arm.
This is what I know so far about the output shaft of the Flaming River box to which the Pitman arm must attach:
The first 5/8" of the shaft is a 5/8"-18 threaded section. This is where the nut that holds the Pitman arm in place threads on.
Then there is a 1/8" length UNthreaded portion of the shaft, to hold the lockwasher that sits bewteen the nut and the Pitman arm.
Finally, there is a SPLINED section of the shaft, which a matching spline on the Pitman arm engages. It is this spline pattern that the custom Pitman arm must have in it, and I am having trouble describing the spline pattern in terms that a machinist will clearly understand.
Here is what I have measured on that splined section:
Diameter is 13/16"
There WOULD have been 36 splines around the circumference of the shaft, i.e. one spline every 10 degrees, EXCEPT that there are four relief cuts, 90 degrees apart, each of which displaces one spline. There are 32 regular splines. (Check the math: 32 regular x10 = 320 degrees plus 4 relief slots x 10 degrees = 360 degrees total). (edited this after initial posting to correct errors)
I am thinking that this spline pattern is the way it is to ensure that the Pitman arm is correctly "clocked" relative to the steering box. That is, you cannot just mount the Pitman arm at "approximately" the right angle to meet the drag link; it can only be mounted so that the wide slots are engaged by matching wide ridges on the Pitman arm. This ensures that when the truck is driving straight ahead, the steering box is in the center, "tighest" portion of its internal gearing, where road wander will be dampened.
I am thinking that this specific spline pattern is probbaly some sort of industry standard (I HOPE!), and is probably described in some specific standard way, like, for example maybe 13/16 x 36 with 4 indexing slots???
Is there anyone out there who is a pro mechanic who works a lot on steering and can tell me what the correct "standard description" for this spline pattern would be?
The bottom tapered hole is easy:
The Pitman arm has an "inside" (near the frame rail) side, and an "outside" (away from the frame rail) side
Pitman arm thickness at the hole is 0.75"
INside diameter of the tapered hole is 0.655"
OUTside dimater of the tapered hole is 0.733"
But I really need help describing that spline pattern at the top of the arm!
Anyone?
Jim G
Last edited by JimGnitecki; 05/03/2008 2:38 PM.
