Wheel alignment affects safety, handling, and performance. Abnormal tire wear and handling quirks signal the need for wheel alignment. Modifying the chassis or suspension requires a trip to the alignment shop. Wheel alignment is routine service for trucks with a solid, hypoid rear axle and a beam, twin-beam, or independent front suspension (IFS) system.

A vintage I-beam front axle has the simplest alignment needs. If the axle beam is true, the kingpins fit properly and springs do not sag, alignment may be as easy as setting the toe-in of the front wheels. For the truck with IFS, wheel alignment involves periodic checks and adjustment of caster, camber, and toe-in.

Alignment at a modern shop includes four-wheel "thrust" inspection, caster set, camber set, and toe set. Some shops can perform a true "four-wheel alignment," but unless a classic truck has a retrofit independent rear suspension (IRS) system, four-wheel alignment is not necessary.

Thrust alignment takes rear axle shift, worn springs and bushings, or a bent frame into account. A shop that performs either four-wheel or thrust alignment can handle any truck with a solid, hypoid rear axle system. To push the vehicle forward in a straight line, rear axle thrust must be perpendicular to the centerline of the frame. When thrust is correct, a front wheel alignment can assure precise steering and a normal steering wheel position.

Toe Set
Toe-in is the angle that the front wheels point when the steering aims straight ahead. While parallel front wheels would seem ideal, the front wheels seldom call for 0 degrees of toe set. Due to the thrust loads of the vehicle moving forward and the nominal movement of steering joints under load, toe is actually set so that the tires "toe-in" slightly at the front. When turning, the inside wheel has a tighter turning angle than the outside wheel.

Tire design dictates toe-in requirements. Bias-ply tires have a tendency to thrust outward under load. The vintage truck with bias-ply tires should follow the factory alignment specifications. That toe-in might be in the 1/16- to 3/16-inch range, typically a 1/8-inch setting. If using modern radial tires, toe-in should be more like 1/32 inch, actually measured in tenths of a degree, not inches, using modern alignment equipment.

For the older truck with a beam front axle, toe-in may be the only adjustment needed. If the frame and axle beam are straight, the springs set evenly, the kingpins fit properly, and caster angle meets specification, it is possible to do your own toe set adjustments. A simple toe bar can be purchased through automotive tool suppliers.

Point the front wheels straight ahead. On a flat floor, lift the front axle slightly to eliminate load thrust. Support the axle safely. Scribe a line at the centerline of each front tire tread. The toe bar gauge measures the distance between these centerlines, as close as possible to the midline (front and rear) of the tire. This kind of alignment serves well when there are no defects in the steering linkage, steering gear, kingpins, suspension, or wheel rims.

When caster and camber settings are known to be correct, the toe bar will also work on an IFS or twin-beam suspension. Support the front suspension with a floor jack under each lower control arm or the outer end of each I-beam. Lift the wheels evenly, just off the floor, and make sure the vehicle is safely supported before handling the wheels. Scribe the tread centerlines and set toe to specification with the suspension weighted.

With the chassis weighted and the front tires pointing straight ahead, each tire should stand nearly vertical. Viewed from the front of the vehicle, camber degrees are the tilt of the tire from a vertical centerline. If the top of the tire tilts outward, camber is positive. If the top of the tire tilts inward, camber is negative. Alignment specifications read in positive or negative degrees of camber.