Front End Alignment Specs vs Behavior (Return to Center)

[basstrix]

Just curious, what brand / make idler arm did you put in there?
The geometry of some repops may not be as the original and if so, that will undoubtedly cause problems. That could be what is causing some of your issue.
Here's a sketch I did to illustrate what I mean. Sorry, this copy is not very clear.
The part I put in my car was the Rare Parts brand (from NPD) and while it may look different the geometry is the same and I have no issues with steering in that regard.

The new Idler came in a rebuild kit I bought from a member of this forum. I've already thrown away the bag it came in, but its geometry matches what I removed, along with the Steering Arm. It has a PN 3355-A on the arm. The bushing on the Center Link has the same PN as a Moog bushing I have. It looks a lot like the Rare Parts version, but not as beefy.

After reverting back to the old, but still good, Idler, it now returns to center. That Center Link joint was very stiff. Maybe these things break in or maybe the rubber on the one I have has hardened? Also, I put it together dry....maybe it's supposed to get some silicone grease?

Edit: I found a picture from the seller's posting:

 

[Stanglover]

The new Idler came in a rebuild kit I bought from a member of this forum. I've already thrown away the bag it came in, but its geometry matches what I removed, along with the Steering Arm. It has a PN 3355-A on the arm. The bushing on the Center Link has the same PN as a Moog bushing I have. It looks a lot like the Rare Parts version, but not as beefy.

After reverting back to the old, but still good, Idler, it now returns to center. That Center Link joint was very stiff. Maybe these things break in or maybe the rubber on the one I have has hardened? Also, I put it together dry....maybe it's supposed to get some silicone grease?

Edit: I found a picture from the seller's posting:
View attachment 94001

Thanks for clarifying the part you have. Perhaps you're right, a tight bushing.
Now, I have to eat some "humble pie". I went back over my receipts from NPD and found the one for the idler arm I actually bought in 2015. It was NOT the Rare Parts one as I thought. It was 3355-1 but it too matches the old one I took off and still have. In the listing from NPD, it now mentions the upper bolt hole may need to be slotted upward for some installations. That is what got me rethinking my statement because that's exactly what I had to do. Sorry about that or any confusion I may have caused.
Regardless, the sketch is correct in so much that it illustrates the important dimensions.

 

[basstrix]

Thanks for clarifying the part you have. Perhaps you're right, a tight bushing.
Now, I have to eat some "humble pie". I went back over my receipts from NPD and found the one for the idler arm I actually bought in 2015. It was NOT the Rare Parts one as I thought. It was 3355-1 but it too matches the old one I took off and still have. In the listing from NPD, it now mentions the upper bolt hole may need to be slotted upward for some installations. That is what got me rethinking my statement because that's exactly what I had to do. Sorry about that or any confusion I may have caused.
Regardless, the sketch is correct in so much that it illustrates the important dimensions.

Thanks for the insights. When I was replacing the Idler, I set the two side by side and after install, A quick visual confirmed the Center Link was running horizontally and square to the front-rear axis of the car. The attached diagram is representative of what my car has for Idler/Center Link config. In the 1971 manual, I'm seeing two configs. The alternate config has the Center Link registering on the upper surface of Ilder. In my Vehicle Dynamics coursework, I became familiar with Roll, Pitch, and Yaw axis for vehicles. I use Pitch axis to describe the ideal orientation of the Center Link.

 

[Stanglover]

Thanks for the insights. When I was replacing the Idler, I set the two side by side and after install, A quick visual confirmed the Center Link was running horizontally and square to the front-rear axis of the car. The attached diagram is representative of what my car has for Idler/Center Link config. In the 1971 manual, I'm seeing two configs. The alternate config has the Center Link registering on the upper surface of Ilder. In my Vehicle Dynamics coursework, I became familiar with Roll, Pitch, and Yaw axis for vehicles. I use Pitch axis to describe the ideal orientation of the Center Link.

That's a very useful diagram. In it "Y" is basically the same as my sketch except it describes the bottom surface of the bushing, whereas I picked the top. In retrospect, the bottom would be more correct as it is the seating surface for the center link.
In my original 1971 Ford manual, I'm not seeing an alternative configuration and in fact the diagrams are poor to say the least and really don't show much at all. The description isn't much better either.
At the end of the day, if it works correctly, that's what counts.

 

[basstrix]

Here's the alternate...says it's for Montego and Torino with power steering...lists some others, as well. There's something similar for other models having manual steering.