Thanks for the post EricPeterson on Cumminsforum
So there's talk and talk and talk about the Thuren front toe-on specs ( zero or near zero ) vs. the stock toe-in specs ( 1/8" ). And there are tons of comments from guys who adjust toe themselves. And yet in the couple years I've been on here, I haven't actually seen an explanation of that. So let's address determining if you've got too much toe and then the pitfalls of having someone else try to set it for you, and then I'll post some easy pics.
First, there's a simple way to tell if you have too much toe-in long before your tire edges are scrubbed off. Look at the finest cut lines inside the blocks nearest the outer edge -- the sipes. If the back edges of forward-pointing bends in the sipes are lifted and you can feel them bent upwards, you're scrubbing the outer edges of your tires and they will wear too fast. The tire wear surface should be flat. If there are edges of sipes lifted, the tire is seeing deformation and heating that's in excess of desirable wear parameters.
Second, there's no need to take your truck in to a shop and argue with them over which set of specs to use. Some shops will never agree to use anything but stock specs because that's all their computers understand, and some might agree to use a non-stock spec... and use the default factory specs anyway because they'll assume their computers know best. And still others may agree but might not have the expertise to make their alignment computers dance properly to your custom settings. And then there are shops who can't do the work properly at all, under any circumstances. I do not believe in this day and age that that leaves many candidate shops at all.
So... assuming your hub kingpins are tight, and your tie-rod ends are good, it's VERY easy to adjust toe-in yourself. Get some good duct tape and two identical plumb bobs for carpentry work. An additional tool might be a stable linear straight edge 8-feet long, like a nice piece of aluminum tile flooring threshold, or a simple piece of hot rolled steel flat. In a pinch you can use a tape measure, but you'll likely need a helper to hold it.
Step 1: Jack your front axle so that each front tire is just barely off the ground. I use two jacks -- one under the pumpkin and one under the cast reinforcement on the long side -- so I can get each tire just at the right height.
Step 2: Duct tape a plumb bob line to each front tire's forward side, approximately on the centerline, so that the bob hangs with its pointer just off the ground and the tape holding the line securely at that point where the line touches the tire tread. They don't have to be exactly on the tire centerlines; we're dealing with a difference here, so the errors zero out.
Step 3: Take a stable linear reference -- like hot rolled flat shown in the photos -- and mark the locations where the plumb bobs point. I moved the flat until it was even with one side, and used another piece of duct tape to make the other side.
Step 4: Rotate both tires so that the plumb bobs are hanging behind the tires. Move the straight edge behind the tires too. Take a look where the pointers fall. You'll note in the 3rd and 4th images that the right bob falls about an eighth of an inch further outboard than in front. This is 1/8" toe-in.
I locked everything down at this point and after a day of driving noted that the back edges of my outboard sipes were lifting. Too much toe-in. I repeated the adjustment, turning the tie rod adjustment longer until the distance between bobs front and rear was as identical as I could make it, with perhaps only a touch of toe-in. This required only about 45 degrees of turn on the adjustment sleeve on my Synergy HD tie rod assembly. This is near-zero toe. Locked it down again. Done.