I'd start by making sure the wheels are straight ahead. Disconnect the drag link, then remove the pitman arm. Now turn the steering wheel lock to lock a couple times counting the turns. starting at one lock turn it back 1/2 the number of turns to center the box (ignore the steering wheel position at this time). Reinstall the pitman arm so it is vertical. Measure the distance from the steering arm ball to the center of the pitman arm pivot, this is your new center to center length of the drag link. Do what ever is required to make a drag link of this measurement. If the tape measure was at a significant angle from horizontal when you measured, build the new drag link with a lazy "Z" from the side so the ends will be horizontal when installed. Don't forget the shallow bend from the top as well (check out your stock 56 draglink to see what I mean). After all this you may need to drop the tie rod to prevent interference. Mid Fifty sells spacers. (Oh what we do for beauty!)
With your new draglink in place, the wheels straight ahead the steering box centered, and the pitman arm vertical, Finally take the steering wheel off and reinstall straight if necessary. Now go out, drive around, and enjoy!

 

AX, I did not see mention of wanting the drag link parallel to the ground/garage floor. Important?

 

The lazy Z will do nothing different than if the drag link went directly between the two points or went around in a half circle. The steering arm will still move the same. The best way to eliminate bump steer is to have the steering arm knuckle and the pitman arm knuckle mounted at the same height as asked about in the above post. If the pitman was mounted directly beside the spring mount, preferably at the opposite end of the spring from the shackles, there would be no bump steer when the wheels were pointed straight ahead. The movement of the axle would have the same arc as the spring and the drag link. There would be no change in the relationship of the two components.
In one of the beginning posts, there is a reference to toe-in, caster, camber, etc as a cause for bump steer. If the truck has a solid beam axle, which I assume this one has, nothing in the above list changes as the axle goes up or down. Neither the toe in, caster, nor the camber changes in the movement of the axle. The change in geometry is in the relationship of the steering arm and the pitman.
If you draw this out on paper, you will see that the wheels will turn as the axle move up or down and the pitman stays still. A longer drag link will show less bump steer. A pitman knuckle at the same height as the steering arm knuckle will show less movement. This can be drawn out with the help of a protractor.

 

In an ideal world yes. you would want the steering arm pivot and the pitman arm pivot to be the same height above the ground/floor. If I were doing Imlower2's steering linkage I would either raise the pivot on the pitman arm (may not be possible/practical depending on the box ratio, and or lowering the pivot on the steering arm (possibly flipping the ball to the bottom of the arm?). This may also cause complications by causing interference with the tie rod? My ideal solution would be to swap the unknown box for a Toyota power or manual box and be done with it! They just work like they were made for it.
Barbsbuddy you are 100% correct, The caster and toein will make the steering track more true and less likely to follow undulations or cracks in the pavement, more correctly called tramlining, but often lumped under the general title of "bump steer". Camber is built into a beam axle and is not changable on a practical scale.

 

Ok, here's an update on what happened today. I went to the alignment guy who set my toe in, toe out. It was slightly toe out so he adjusted it 1/8" toe in. The caster was OK, the camber was not consistent either. One side had slightly more 3 degrees and the other 1 degree. We just left it at that. The truck drove pretty nice and at least drove straight. The bump steer was still there, but not nearly as bad a before. So I got home and pulled the pitman arm and the drag link. Set the steering at center and put the pitman arm on vertical. Steering wheel and pitman lined up perfect for the top bolt. (good sign) BTW- the steering was a full 6 turns of the wheel, so 3 was my center point. The drag link was about 2 inches too long in that position. So I took it to my buddy's fabrication shop and he happened to be there (working on his Henry J) He shortened the drag link by two inches. I put it on and noticed that I still have a slight angle with the pitman arm being lower than the steering knuckle. I notice someone on the drop axle bent the lower portion of the steering arm to avoid using the tie rod lowering bracket, which was a trick in the earlier days before they made the drop down bracket. What this did, was lifted my steering arm (ball portion) above the axle causing the draglink to have the slight angle. I took out the torch and attempted to heat it up (the upper arm ball end), possibly bending it down slightly to its normal position. The sucker wouldn bend for anything. Or maybe I was doing something incorrect. The metal got red but would not bend. So, AX, Barbsbuddy, anyone have suggestions on bringing that arm down to make the draglink level? Once again, you guys have really been there helping me out here. Wouldn't of been able to get where I have without the advise. Much appreciated and will hopefully never have to do this ever again. LOL...
Ed

 

Ed, the steering arm is forged steel, it's going to take someone with a very BIG MF press or a blacksmith to bend it. I believe Mid F sells spindles with dropped steering arms. Problem is it requires 2 bends, one to bend it down, the other to bring the ball back to vertical. Like with dropping a stock axle, dropping the steering arm by bending will also shorten it relative to stock length, a smith can stretch it while putting the proper bends in it and retemper the steel after if they know what they are doing. Steering components are too critical to DIY IMHO.
Edit: If the angle is slight enough that the ball socket does not bind on the arm at the limits I'd try it like it is. A shallow angle will bump steer a small amount, but likely not enough to be noticed any more than undulations in the road that we already automatically correct for while driving.
Drag link 2" too long!!! no wonders you were having problems!

 

I put it together and the angle is not too bad. I still have the original steering arm from the original axle. However I already paid to have the alignment done . I could replace that whole arm and even use the drop tie rod bracket from MF if need be. Haven't driven it yet, but will today. The angle is slight now that I shortened the drag link. I owe you a load of thanks AX.

 

Thank me after you drive it!

 

I drove it! Thank you AX. Hope I can return the favor.....
Ed

 

I guess it works better now then?
Glad to be of help!

 

Actually, I only hit two parked cars on the first try out... J/K...I noticed a big difference. It's still not perfect, but it drives nice. The other front end had some steering issues too, so I'm real happy with the way it drives right now. AX, you ready to help me install the four link in the rear????

 

Sure, but unless you are going drag racing I'd skip the complexity of the 4 link and do a trailing arm instead. If it's good enough for Nascar cup cars it's good enough for me.