All good points, Megatron, each deserves an explanation, so here we go...I'll begin by sharing that I ran a four-wheel alignment rack at a GMC truck dealership in the mid-'80s, the era of both beam front axle 4x4s and IFS 2WD and 4WD front ends. For fifteen years prior to that, I had been doing alignment with far less equipment than that new Hunter four-wheel, electronic light beam rack. Fifteen years after the dealership stint, I taught wheel alignment at the adult vocational training level and merged my varied equipment experiences, which reflect in what I'm now sharing.
It's great to use precision four-wheel alignment equipment. However, "computer" alignment equipment is also limited in many ways. For example, you describe aftermarket wheels, suspension and tires, and you're right, of the three (assuming the suspension kit is as adjustable as yours), the wheel offset is the most critical modification. Because your truck falls outside the OEM guidelines built into the software for modern alignment equipment, many shops will avoid doing your truck's alignment.
Reasons for refusal include "liability", "unpredictable results" and "possibility of abnormal tire wear"—regardless of the alignment procedure. In many cases, the shop simply doesn't know what they can do to address or compensate for your modifications...After all, this is the era of plug-and-play. Follow the flow charts or stare at the computer screen or scanner. Wait long enough, and maybe an answer will materialize...That's not going to happen here!
For now, let's suspend judgment about why your truck and millions of other 4x4s are in this predicament. You've installed all of this hardware, and it's time to make the vehicle track as safely as possible—and for the tires to last.
As for front axle lateral alignment, your adjustable track bar is a real asset. Alignment does reference from the rear axle, and for good reason. The term "thrust" is just what it sounds like: The rear axle on a RWD vehicle is the traction point, pushing the frame and the entire vehicle forward from the rear. Unless you're driving backward, your rear-drive truck requires the front axle to align squarely under thrust. (Thus the term "thrust alignment"!) The axles must be square, in any case.
To illustrate, draw a line forward and perpendicular to the centerline of the rear axle. This follows the driveline in approximate terms—unless the driveline is offset like with a side-drive transfer case. This line of force, aimed forward and perpendicular to the rear axle, becomes the reference point for the front axle's position. The front axle ends up parallel to the rear axle, which is simple to visualize on beam axle trucks like our Ram 3500 models. The front axle must also align sideways or laterally, the reason for your adjustable track bar.
Whether the frame is perfectly square or not, if the front axle is parallel to the rear axle (plane view from the top), and if the axles center laterally with each other, you can align the truck's front end. The frame should be square, though, because an out-of-square frame would place the springs, suspension arms and steering linkage at odd angles with the axles.
So, let's start with a square frame, no collision damage, and a rear axle that sets squarely in the truck. It's much easier with our leaf sprung, beam rear axle: The centering points for the rear axle are simply the leaf spring center bolts and the axle's spring perch holes—plus any spacer block alignment holes or pins.
Rear axle in place, you can use the string-in-diamond method for setting the beam front axle's position for both parallel to the rear axle and laterally on center. I used the string method for two illustrated how-to articles at the magazine: my Jeep XJ Cherokee 6-inch long arm installation at the "Jeep XJ Cherokee & MJ Comanche 4WD Workshop" (see the left panel menu) and also the Jeep TJ Wrangler Rubicon Full-Traction Ultimate 4-inch lift. The XJ Cherokee is similar to our Dodge Ram trucks with link-and-coil front suspension and leaf springs at the rear. Both Jeep vehicles have beam axles front and rear.
Critical to a string-in-diamond beam axle alignment is finding precise reference points at each of the axles. You must have a reference point at each side of the front axle that is truly equal distance from the axle's centerline. The rear axle on our trucks is simple: Use the leaf spring center bolts as the rear reference points. On a Jeep TJ or JK Wrangler, there are matching suspension points that are equidistant from the rear axle's centerline.
The front axle should align with equal string lengths to the rear axle, measured in cross or "diamond". This means measuring from the front axle's left side reference point to the right rear spring center bolt, then from the front axle's right side reference point to the rear axle left side spring center bolt.
This measurement must be very accurate. Even 1/16"-1/8" variance can make a difference. If there are obstacles under the chassis that prevent an accurate measurement, you may need to relocate your reference points or even make "extensions" from the reference points to below the obstacles...For these measurements, you can have the axles suspended to full drop, which may help the string lines clear the transfer case skid plate, the exhaust or any other objects in the way.
Be creative. It's crucial that your four reference points reflect equal distances from the center of each beam axle outward to each axle's reference points. Strings then measure in cross between the front and rear axle reference points.
Again, the end game here is to have the axles parallel and tracking in line with each other. When the front axle is offset laterally, one way or the other, we call this "dog tracking".
Note: Don't be confused if one axle's track width is actually slightly wider than the other axle with the wheels in place. Some trucks (G.M. beam axle 4x4s come to mind) were designed this way, typically with the front axle slightly wider than the rear. I won't digress into "why" this was the design, simply know that if your reference points match side to side on each axle, and if you run the string lines in cross to matching points at the opposite axle, you will determine both the square and lateral alignment of the two axles.
Checking for square with two strings-in-cross is a simple function of geometry. If anyone is having difficulty understanding the principle, draw a perfect square on a piece of paper; now draw an "X" from opposite corners, intersecting at the middle. Measure the length of each "X" line. It will be equal. If you now use a rectangle instead of a square, the results will also be two equal length, intersecting lines. Play with this, and then transfer the "X" lines to your truck's chassis: On your long wheelbase Dodge Ram 3500 truck, the beam axles represent the short ends of a rectangle.
The most elaborate "4-wheel" alignment machine will not produce any more accurate results than doing a string line test properly. Once you get the axles square, you can concentrate on a front wheel alignment. This, as you say, is not rocket science, and it's even easier with a beam front axle.
Camber, in particular, is factory pre-set on a beam axle. Camber measurement indicates the degree to which the axle beams, steering knuckles and ball joints are in alignment. As you mention, you can make camber corrections with off-set ball joints, or eccentric ball-joint seats, and a source for such parts is Specialty Products Company.
Caution: I am against "bending" beam axles to correct slight camber issues unless a racing, weld-on truss is part of the straightening process. (Be aware, too, that welding on a truss is a good way to warp an axle and alter camber!) Consider the axle tube and center section materials plus the original stress that caused the axle to bend. There are metallurgical changes that take place with cold or hot bending. If you need to correct for a slightly bent or out-of-spec axle beam, use offset ball-joints or eccentric ball-joint seats. Make sure the bend did not stress-fracture the axle pieces. Toss out the axle housing if in doubt—you can transfer internal pieces and add-on goodies to a new housing. (See the magazine's many axle rebuilding articles and the HD videos on axle setup.)
Be aware that beam front axles come from the factory with +/- camber often slightly beyond the factory recommended camber degree range. I have seen this on Dana Jeep front axles, typically at the short beam side with more factory welding. An extra 1/8 to 1/4-degree camber at one side is not earthshattering and likely was acceptable during OEM axle assembly and installation. This will not impair vehicle handling and has negligible effect on tire wear if you rotate your tires on time. If you are adjusting caster and camber with offset ball-joints or eccentric ball-joint seats, bring both the caster and camber within their recommended degree ranges.
To answer your questions about "do-it-yourself" alignment, go no further than these three features that I've done at the magazine. They each get brisk traffic, addressing alignment goals with inexpensive solutions for doing your own alignment work.
First is the ‘DIY’ feature on a beam front axle wheel alignment. This is a useful article for understanding the principles of front wheel alignment as well as a 'how-to' on using an affordable SPC Off-Road Fastrax 91025 gauge kit designed for tires to 44" diameter. Click here to see this DIY how-to and equipment article.
For those on a shoestring budget, a single gauge kit will do. You can even improvise on the need for turn plates. SPC suggests using plastic sheeting beneath the front tires for a slip surface. On a beam axle, you can unload the weight slightly with the use of two floor jacks, raising the weighted axle evenly and just enough to take the heavy load off the front wheels and tires. This provides easier wheel turning.
There is also a photo closer to home, my Dodge Ram 3500 4x4 alignment after installing the Mopar lift kit. Here, I purchased inexpensive front turn plates ($100 for the pair!) from Gil Smith Racing at New York. Gil is a personable family guy, and these plates do the job despite the massive front end weight of the Cummins engine, 9.25" beam axle and 500 pounds of Warn bumper with M12000 winch and stainless wire.
For the Dodge Ram alignment, I added a second Fastrax 91025 alignment gauge kit from SPC to make toe setting easier and quicker. This way, you can use the winged braces and separate gauges at each side of the truck during the alignment procedure. This eliminates the need to swap a single gauge set from one side to the other.
Last, but surely not least, is the HD video walk-through of alignment on a Jeep TJ Wrangler Rubicon. You'll like this for both a visual orientation and added quips about the process. In this HD video, I do use the double alignment gauge sets from SPC and the Gil Smith turn plates. You’ll see how this speeds up the process.
Some additional pointers on doing your own alignment at this level: 1) make sure the floor is flat in both directions or compensate when taking the measurements with the bubble gauges, 2) make sure the turn plates are thin (like the Gil Smith type) or if you spring for more commercial type turn plates (available from several sources, do a Google search under "wheel alignment turn plates"), make sure you raise the rear of the truck to compensate for the turn plate height at the front. Even with a 140.5" or longer wheelbase, a sloping or leaning truck will throw off your camber and caster readings with the SPC 91025 bubble gauges...If you want to add a touch of professionalism, purchase a pair of rear slip plates from Gil Smith Racing that will enhance the work and raise the truck's back end to match the front turn plates.
As you mention, always save the toe-in setting for last. Camber and caster angle must be right, with the vehicle setting at static (curb) height on the ground, before setting toe. I use factory toe-in and caster angle settings, and the Dodge Ram handles very well. And, yes, caster is important, this and steering axis inclination (SAI) are what return the front wheels to center after coming out of a corner.
The surest sign of too little caster angle is a vehicle that requires turning the steering wheel back to center after a turn. I'm at 4-degrees positive caster on the Dodge Ram 3500, closer to 7-degees positive on the XJ Cherokee. More can sometimes be better for off-pavement turning radius; however, factory specs are the best for normal tire wear and handling in general.
I mentioned another specification that is of concern during alignment: steering axis inclination (SAI). We can go into this if you want, but the important thing to note for DIY alignment purposes is that strange caster and camber angle readings over the full turning arcs (illustrated in the XJ Cherokee alignment how-to article and shown in the TJ Wrangler HD video coverage) are an indication of a bent steering knuckle on a later beam axle 4x4 or a bent spindle on 2WD and vintage 4WD vehicles.
On alignment equipment that will identify SAI error, if all measurements are correct and SAI is off, we inspect the steering knuckle, spindle or unit bearing hub for damage. Make sure any strange readings are not from bad steering knuckle ball joints or worn wheel/hub bearings! Better yet, inspect for ball joint, wheel bearing and unit hub bearing wear before attempting the alignment. Check steering linkage for loose joints, too.
This is ground school, we can go from here. As a light- and medium-duty truck fleet mechanic in the late 'sixties, I began aligning my own beam axle Jeep CJ3A and vintage '55 Ford F100 at home. On these vehicles, toe-in could be set with nothing more than a tape measure. If you do wheel alignment with turn plates, the steering linkage and suspension will be unloaded, and the measurements will be that much more accurate. Add rear wheel slip plates and Fastrax gauges, and you can emulate a "pro" alignment!
Even on the vintage 2WD and 4WD fleet trucks with beam axles, I did quick, rough-in beam axle wheel alignments with nothing more than a tape measure or a portable, adjustable "toe bar". Floor jacks were placed evenly under the axle at each side. I would lift the axle beam just enough to "unload" the wheels and tires. Before setting toe, I made sure the wheel bearings and kingpin bushings or bearings were in good shape and adjusted properly.
Tape measure alignments on the trail are often necessary when someone bows a tie-rod on a tall rock or snaps a tie-rod in half. A Ready Welder tie-rod repair at Moab's Rose Garden is just one place where your tape measure alignment skills would be popular. This can get a vehicle home from the trail and tracking down the road safely to a wheel alignment shop. When using just a tape measure for toe-set, make sure you follow the tread pattern closely at the front and rear midline of the tires.
When using turn plates to unload and center up the steering linkage and suspension, it helps to bounce the front end. Push down on the front bumper a few times—the bumper is conveniently located at waist height on your Mega Cab!
If necessary, use a pair of floor jacks under the beam front axle to take weight off the wheels and tires, then lightly rock the steering wheel at its center position before setting the front tires and steering wheel to straight ahead. This will unload the steering linkage for more accurate alignment settings.
When using a tape measure only (not the Fastrax 91025's wing arms), always measure matching tread points. Measure as close to the midline (3 and 9 o'clock) of the tires as possible. Avoiding obstacles is sometimes difficult, but midline of the tires is preferred. Always set toe-in, followed by centering up the steering wheel. You center the steering wheel by adjusting the steering linkage sleeves—never by removing the steering wheel and repositioning it!
Caution: The steering wheel spokes are factory set to align with the center or “high” point of the steering gear in the straight ahead steering position. Bring the front wheels into alignment with the centered steering gear and steering wheel—not the other way around! If the steering wheel has been repositioned from factory, find the precise center point of the steering gear. Position the steering wheel there before aligning the front wheels to straight ahead. This also applies when making fine steering wheel position changes after an alignment: Adjust the steering linkage sleeves, do not reposition the steering wheel! Always check toe-in again when you center the steering wheel.
To illustrate how well you can do a 4-wheel alignment with strings, a tape measure, a common spirit level and a protractor, I installed the Full-Traction Ultimate lift kit on the Jeep TJ Wrangler Rubicon in just that way! The job began with the vehicle on my hoist and as level/parallel to the ground as possible.
I placed a pair of adjustable tripod stands beneath each axle and raised the vehicle straight up, just enough to install the lift kit. The axles remained on the stands with cables and other chassis attachments still in place.
After installing the kit, including a bevy of adjustable link arms and a unique rear tri-mount suspension system, I used the string method to square the axles. The rear axle location, fortunately, was fixed by the kit’s design, so this became the reference for making everything square with the frame. The approach was similar to the rear leaf springs and center bolts on our Dodge Ram 3500 trucks. In our case, the rear springs and axle spring perches locate the rear axle squarely at the frame.
I set the caster with a quality bubble level and a 180-degree, indexed protractor. I set toe-in with vehicle weight on the axles and tripod stands, using a tape measure fore and aft (as close to 3 and 9 o'clock as practical) at the front tire midlines, keeping the tape as level and parallel to the floor as possible. In my view, this was all just a preliminary, rough adjustment.
The next stop was a friend's shop with a $40K alignment rack capable of 4-wheel "thrust" alignment. On the alignment rack, to everyone's surprise, the entire suspension system took only one-half turn of one threaded link arm tube to be fully square! Caster was on, camber (non-adjustable on a solid beam axle) was okay, toe-in and centering of the steering wheel were just routine, slight adjustments.
Caster angle was within spec and did, as you describe, provide an acceptable angle for the front/pinion U-joint flange. With a double-Cardan (CV) joint at the transfer case, there is some leeway on this front axle pinion joint angle, and the compromise is between caster angle and U-joint angle. Like you comment, caster usually wins if you want the vehicle to steer correctly!
For modified trucks with suspension lifts and oversized wheels and tires, there are two very important considerations for handling. First, the aftermarket wheels' offset and the tire diameter must provide the right intersect point with the ground. This is the “scrub radius”.
Visualize the front wheels pointed straight ahead. Draw a line through the ball-joint stud centerlines and observe where that line intersects the tire tread at the ground. This point must be similar to the OEM wheel/tire intersection point, or you will swing the tire on an odd arc during turns, resulting in strange handling and premature tire wear. Scrub radius impacts tire wear as well as handling.
Secondly, consider the arc of radius and caster angle changes as the front suspension (link arms in your case) rise and set. Arc of radius is why we do long-arm kits for dramatic lift. When we increase suspension travel, short arms exaggerate the caster angle changes as the suspension extends and compresses.
Long link arms are the solution for increased suspension travel. Longer arms will create less caster angle change over the suspension and axle’s arc of travel—or radius. Simply put, you can set the caster at static/curb weighted chassis height, and the caster angle does not vary excessively as the link arms move up and down with the axle.
When buying an aftermarket suspension lift kit or bigger/wider wheels and tires, consider these issues. In looking at your Mega Cab components, I really like the stamina and quality of the aftermarket joints, link arms and drop brackets! What you want at the end of the day is suspension that behaves as well as or better than OEM engineering—yet with the lift and tires you desire. Going beyond “looks”, the goal is to understand the demands and dynamics of vehicle suspension and handling. Doing your own wheel alignment is a good start.
As for the rear axle, the usual concern is pinion and driveline angles for U-joint survival. Within reason, you can rotate the axle housing for pinion angle change without affecting vehicle handling, as the rear drive axle’s shafts are not sensitive to caster. (If we were talking about a front wheel drive car or an IRS/AWD car, there would likely be provision for adjusting rear wheel caster, camber and even toe-set.) For our trucks, tall lift blocks at the rear leaf springs can create some issues, mainly traction and spring windup related.
So, you might skip the visit to the local 4-wheel alignment shop and the brief Car and Driver read—likely just long enough for the tech to discover that specifications for your lifted and modified '06 Dodge Ram 4x4 Mega Cab are nowhere to be found in the alignment machine's software program. As an option, consider the SPC Off-Road 91025 alignment equipment...Two kits work even better than one!
Used properly, this accurate, portable SPC setup can help you dial your front end alignment for both safety and good tire life. Bubble caster and camber gauges were an automotive industry standard for at least sixty years prior to light beam, infrared, RF and laser alignment equipment.
I entered the service and repair industry when we were still called "mechanics", and breaker point ignitions were the norm. Smaller shops used floating caster/camber bubble gauges that fit magnetically to the end of front wheel hubs! Professionally, I've spun wrenches all the way into the contemporary electronic fuel-and-spark management "technician" era. Electronic, beam four-wheel alignment equipment has been in vogue for more than three decades now...I find it advantageous to have walked in both worlds.
Beyond alignment, make sure that the wheel offset and tire diameter add up to a safe and tolerable "scrub radius”. As an alternative to Car and Driver, sift through this Wiki info about scrub radius and SAI. When you widen the wheel rims, you can only go inward so far. (Rotors, calipers and hubs limit the inward wheel position.) For that reason, wide rims almost always offset to the "negative" direction or outward. If there are wheel backspacing choices, match up the wheel width, backspacing and tire diameter wisely! The concern here is the scrub radius.
We lift our vehicles and mount oversize wheels and tires for a variety of reasons. In the end, we get to make the handling and safety corrections that these modifications require. Routine tire rotation is always essential, even more so when scrub radius and arc of radius get compromised. Once you dial the front end alignment to the best point possible, watch for ball-joint wear, wheel bearing or hub bearing wear and any tire issues. This can sometimes be the price for a lift and oversized tires. We can, however, reduce, minimize or even eliminate that risk and expense!