A problem I’ve seen too many times on this forum is someone complaining about a ESP light and their wheel is off. There are always people that jump right in and say
“center it with the drag link, I always do”. This is not 100% the way to “fix the problem”.
First off, let’s start off something we can all relate to. When you are coming out of a turn and let go of the wheel, the tires want to return straight, correct? Okay well there are some reasons for that, along with a given amount of front caster, the spindles move within an arc while the wheel is turned. This is why you will notice the Jeep “lift” some when the tires are turning and stopped, it can be said that at ANY point if the knuckle is not straight, it will want to be straight. We can agree? Now, there is a specified amount where the spindles are “not supposed” to be straight, this is the actual measurement of toe. Which is 1/8” in or less (depending on the rig). When this measurement is achieved THEN you may center the steering wheel. This angle that the spindle makes is called “Steering Axis Inclination”; here is the technical definition:
“Steering axis inclination
Steering axis inclination is the number of degrees that a line drawn through the upper and lower ball joints (or strut and lower ball joint) and viewed from the front is tilted to the left or the right. This, in combination with caster, is responsible for the directional stability and self-centering of the steering. As the steering knuckle swings from lock to lock, the spindle generates an arc, causing the vehicle to be raised when it is turned from the straight-ahead position. The reason the body of the vehicle must rise is straightforward: since the wheel is in contact with the ground, it cannot move down. However, when it is swung away from the straight-ahead position, it must move either up or down (due to the arc generated by the steering knuckle). Not being able to move down, it must move up. Then, the weight of the vehicle acts against this lift, and attempts to return the spindle to the straight-ahead position when the steering wheel is released.”
What does SAI have to do with the steering wheel not being centered?
Here is a picture of the basic steering design in our JK (our tie rod is lower, the axle is passenger side drop, but it's the best i could find). If the tie rod had a bend in the middle of it (up, or back toward the axle as if you hit something) the distance between the two spindles will lessen. Agree? That not only is called “toe-in”, but that is also affecting what I mentioned earlier. I stated, “It can be said that at ANY point if the knuckle is not straight, it will want to be straight.” Therefore if the knuckles are now pointing toward each other, they are NOT straight (however remember I also stated there is a specification for that which must be followed for it to work properly). Anyway, so your toe-in was set to 1/8” when you got to the trail, and it’s now 3/8” toe-in after attempting to crush granite with the tie rod; ¼” too much in. That is going to be a problem, your steering wheel was set to run where the tires are equally 1/8” apart, now that they are 3/8” apart, the tires will want to center the best they can (SAI), which usually it will pick one tire and the other will take up for the entire ¼” out of spec. Which tire it favors can depend on tread height, tire pressure, tie rod end slop, etc, however it will be defined. You’ll have a wheel that is “off to the right” (or the left depending on the wheel). In doing so this moves your steering wheel off-center.
Now if you are like some here, you’ve talked to a guy, that’s talked to a guy, which had a guy tell him “straighten the wheel with your drag link adjustment”. Will that straighten the wheel? You betcha. Will it fix the problem? Probably not, the problem is the toe is likely out of specification, if you bent your tie rod 99 times out of 100 resetting the toe to where it was WILL center the wheel again. Magic? Nope, it’s just where it was when you started the trail with 1/8” toe in.
Now back to just the drag link itself, it’s puny and weak. Can the link itself bend and throw the wheel off? Sure it can, however that should not be the first thing you go to, in my opinion. The tie rod is much more vulnerable to making contact, and is notoriously known for bending solely in fear as you line up to head through an obstacle (sarcasm). Don’t rule out a tweaked drag link, but be sure the toe is correct, then adjust it if necessary.
I hope that makes some sort of sense, if someone has a discrepancy with what I wrote, it is not gospel.
It’s my take on the problem and will be more than happy to discuss/change it for the overall good for the “drag link adjusters”.
Now how can you adjust the toe yourself? It's quite simple with another set of hands and a tape measure. Put the wheels as straight as you can by eyeballing it, be sure to be on some sort of level ground..it doesn't need to be flat, but level. Find a common point within each front tire (KM2s have a perfect little line through the middle of the tread to measure from).
Measure from that point across the front of the front tires, write it down. Do the same measurement from the backside of the front tires. If your first measurement is shorter than your second, you have the tires toed in (opposite for toe out). The adjuster is on the drivers side, loosen the bolt and turn the adjusting sleeve to achieve the correct toe, then retighten the bolt. You'll need some channel locks or a good pipe wrench to turn it. There are also approximately 1,001 threads/write-ups on DIY solid front axle alignments on the interweb.