Steering Pitman Arm - Shop Manual

One Good Turn Deserves Another
Q.I was paging through the February issue of STREET RODDER and read the article you wrote about old Ford suspensions. I thought I might bring up a point about the line on page 58, which states: "When the steering wheel is centered, the Pitman arm should be 90 degrees to the drag link." I'm just an amateur old backyard builder, but I've always done mine a little different. For instance, if a Mustang steering gear is used with the Pitman arm pointing up, and if the angle is 90 degrees as you state it should be, what happens is that since the left spindle turns more in any left turn, the angular movement will be more since the Pitman arm moves more. In the opposite turn, the left spindle turns less than the right, henceforth needing less angular movement from the Pitman arm. If you lean the Pitman arm rearwards by approximately 10 degrees, what happens is that for the same degree of movement of the Pitman arm, the linear distance moved by the drag link will be more in a left turn and less in a right turn which is what the left spindle needs. (You agree with this in an earlier sentence that states: "When a car turns a corner, the inner wheel must turn tighter than the outer.") Play with this one a little and I think you will understand what I mean. I would appreciate a response, and would be glad to support this argument with sketches if you have trouble with my written explanation.

Tom Eckholdt
Via the Internet

A. We responded to Tom with our justification for positioning the Pitman arm as described in the article, "Traditional Tech-The Science of Straight Axles." Evidently we didn't overwhelm him with our logic, and Tom wrote back and included the following drawings:

Suffice to say that after numerous emails going back and forth neither of us succeeded in changing the mind of the other. And perhaps that is the point of this hobby: doing things your own way.

In terms of the subject at hand, Tom's emphasis was on equalizing steering effort and the number of turns from center to full left and right lock. To accomplish that with his Mustang steering-equipped example, he advocates leaning the Pitman arm to the rear. While that does indeed accomplish his goal, his goals and ours are not the same. By moving the Pitman arm off center (other than 90 degrees to the drag link) the travel is indeed altered but so is the steering ratio one-way versus the other.

As far as we're concerned full-lock turns are seldom a concern other than parallel parking or making a U-turn (or if you're into drifting) and it's not unusual for a car to turn sharper one direction than the other. And if the steering wheel turns half a revolution more to go full-lock one way compared to the other, so be it. We're more concerned with road manners, and prefer uniformity in steering response immediately off-center for making the countless steering corrections necessary when driving down the road and negotiating turns made at speed.

To make our point we imposed on Brent VanDervort of Fatman Fabrications to use a CAD program to diagram steering movement with the Pitman arm at 90 degrees and 105 degrees to the drag link

After a considerable number of emails to Tom and phone discussions with Brent about steering design he summed it up this way, "All this science is interesting, but in the end I'm not sure it's a really big deal. In the real world, I don't think most folks would notice the difference. So maybe both theories lack a little."

So where does this leave us? Depending on which theory you align yourself with, we're right back where we started. Brent most likely hit the nail on the head: it's probably true that most people wouldn't notice the difference one way or another. Nonetheless we'll continue to install steering the way we've always done it with the Pitman arm 90 degrees to the drag link. Tom will most likely continue to do things his way and no doubt there is someone out there with yet another opinion. Let us know if you have one.