Very accurate if you measure accurately. To start, loosen clamps on both steering turnbuckles, degrease and de-rust both, oil them so they turn easily. I used Muriatic Acid to remove the rust, turning both turnbuckles to allow the rust to run out, then rinsed and cleaned with spray solvent (brake cleaner spray) then used heavy machinist oil to lube the threads.

Suspend both front wheels on axle stands, tires off the floor the same height. Set the rear tire air pressure as high as safe so the sidewalls (hopefully) are "square".

Use a long metal ruler or level to "scrape" down across the wide portion of each tire sidewall to show where the sidewalls are the widest- those points are where the cord is measured to later.
If you have a stiff metal straight-edge, tape it across the tire sidewalls to establish a flat plane.

Set the steering wheel cross bar horizontal, front tires straight ahead.

1.) 3/16" "550 Paracord cord", not string. String is too flexible.

2.) Front wheels are WIDER than the rear so the cord must be spaced away from the rear tire sidewalls about 1-1/2 inch. Wood block at the rear of rear tire. The cord was tied thru the wheel rim. This eliminates one variable and one measurment for more accuracy.

3.) Heavy, solid concrete block in front, cord as TIGHT as possible, to allow a machinists rule to contact the cord without moving the cord.

4.) Use a "Machinists Rule", NOT tape measure. Tape is very sloppy. Search for "GENERAL TOOLS Steel Rule: 300/1". The cross bar is VITAL for accuracy as it helps align the rule perpendicular to the tire sidewall for accuracy. Read about "parallax" - thats what accuracy here is all about. Lay the rule on the cord, touch the rule to the "wide point" on the sidewall.

5.) Measure from the cord inner edge to the "wide" point on the tire sidewalls with the rule lying on the cord and the "Tee" on the rule aligned with the inside edge of the string. Its critical to align the tee with the cord, else the rule will be tilted front-to-back and read too high. Measure to a 32nd of an inch.

6.) If needed, adjust the turnbuckle nearest the Power Steering box to align the DS front wheel straight in line with the rear. As either/both turnbuckes are adjusted, the steering wheel will tend to move, after each adjustment, check the steering wheel for a horizontal cross-bar.

7.) Do the same procedure for the PS with another section of cord, wood spacer and concrete block. Dont remove the DS cord and concrete block yet, thats what (tries to) guarantee that accuracy is transferred from DS to PS! Dont measure alignment from one front wheel across to the other, too inaccuate- its the 10 or so feet of cord from the rear wheel that gives accuracy. Adjust the turnbuckle near the PS front wheel, check steering wheel after each adjustment (or have a helper hold it).

8.) Adjust the turnbuckes EXACTLY, not "close" with the gap down... when adjusted exactly, the gaps will probably be 'up" so they collect water and rust inside. After adjustment and test driving, seal the turnbuckle gaps so water cant get into the threads. Put RTV sealant in the thread gap or maybe that wide self adhering silicone tape.

Its a bit improper to use the tire sidewalls, this allows the most accuracy, in theory, unless the sidewalls are distorted. The best is to measure from the wheel rims. These tires are brand new Michelins pumped up to 40 psi so the sidewalls are square.

Accuracy from DS to PS is assured from the fact both rear wheels are parallel as they are referenced to the same rear axle housing and wheel bearings. Its possible that if the rear axle has hit a big tree or rock when off-roading that one side axle tube could be out of alignment. A very small rotation of the rear axle on the springs isnt a crisis as what matters is having all four wheels straight ahead. Check rear axle alignment by measuring between both cords and the front of the driveshaft tube.

 

Use dial calipers, measure to the outside edge of the wheel rim, much more accurate. I just tried this again, there was significant difference between the tire sidewalls and rim.

The wheel bearings MUST be corectly set and not loose.

 

Great writeup!

 

Nice write-up with picture.
Measuring on the rim is the thought that came up reading your thread. We always try to measure on the rim. Tires can have quite some bumps on the sidewall.