The quest to drive in a straight line

[BentleyArnage]

I have 3 of these things. They steer sloppy. I have no problem with it. It drives my son crazy. Pitman arm, loose box and its all over the place.

 

[OR VietVet]

If the correct caster lead is not set at alignment, after steering and suspension components replacement, you can still have a wandering effect.

 

[exp500]

My experience on this vintage is it is difficult to get enough caster. After all the worn parts replaced, still drives a little bit twitchy. Gearboxes wear fast, Pittmam/idlers wear, ball joints wear fast. I like to see 3 or more degreees caster (average), on these 1.5 seems to be considered normal. Specialty products makes adjustable upper ball joints AND offset bushings. The bushings are good for 1 degree. The problem is is that requires an alignment shop that knows what they are doing or at least cares enough to tell the truth. If they are knowlegeable and helpful, you can swap out parts enough to make it good then have them align it, without a good diagnosis you are kinda driving at night with the lights off. Too many toe and go shops(at least around here). If you are at the limits of your adjustment pins, and still only have 1.5-2 degrees caster and it still drives funny unless toed .90-.125 or more then you are a candidate for the above. Tires at $1000.00 a set or more, you want to last 50000 miles and gas mileage -2 with more than about .080 toe.
Comes down to build it cheap, build it fast and fix it later design. Hope this helps.

 

[OR VietVet]

But the caster should not be set the same for both sides. The right side should have a slightly higher setting. For instance 1.5 on the left and 2.0 on the right. This offsets road crown.

Or as you said, some helper components may need to be installed instead of stock items.

Or, again as you said, that gear box may have been adjusted too tight and driven long enough that the box is needed.