Alignment: Description and Operation

Caster and Frame Angle (Positive Caster Shown):

CASTER
Caster is the deviation from vertical of an imaginary line drawn through the ball joints when viewed from the side. Caster is directly affected by frame angle. Frame angle is measured at a flat area of the frame forward of the rear wheels and will vary with vehicle loading. The caster specifications will give the vehicle the best directional stability characteristics when loaded and driven. The caster setting is not related to tire wear.

Negative and Positive Camber:

CAMBER
Camber is the vertical tilt of the wheel when viewed from the front. Camber will not vary with frame angle. Camber can be positive or negative and has a direct effect on tire wear.

Econoline caster and camber correction requirements are factory-determined. Adjusters are available to correct a caster/camber measurement that does not meet specification. Before changing the production caster/camber adjuster, thoroughly inspect the suspension system to locate worn or damaged components that may have caused the setting to change.

Positive Toe (Toe In):

Negative Toe:

TOE
The vehicle toe setting:
^ affects tire wear and directional stability.
^ must be checked after adding aftermarket equipment, such as a snowplow or body.
^ must be brought to specification under the load conditions typical for more than 50 percent of vehicle use.
^ must be adjusted only after the caster and camber have been brought to specification.





WHEEL TRACK
By design, Econoline has a front track that is wider than the rear track.

Dogtracking:

DOG TRACKING
Dog tracking is the condition in which the rear axle is not square to the chassis. Heavily crowned roads can give the illusion of dog tracking.

WANDER
Wander is the tendency of the vehicle to require frequent, random left and right steering wheel corrections to maintain a straight path down a level road.

SHIMMY
Shimmy, as observed by the driver, is large, consistent, rotational oscillations of the steering wheel resulting from large, side-to-side (lateral) tire/wheel movements.

Shimmy is usually experienced near 64 km/in (40 mph), and can begin or be amplified when the tire contacts pot holes or irregularities in the road surface.

NIBBLE
Sometimes confused with shimmy, nibble is a condition resulting from tire interaction with various road surfaces and observed by the driver as small rotational oscillations of the steering wheel.

STICKY STEERING
Sticky steering (pointing) occurs when the self-aligning forces, or moments at the tire patch, are not enough to overcome friction or resistance in the steering system.

^ Under normal conditions, these forces assist the driver in returning the steering wheel to within 20 degrees of where the steering wheel was positioned when driving straight ahead.

^ A steering system with excessive resistance can hold the vehicle in a slight turn (or tend to stay pointed in the direction of the turn) when the steering wheel is fumed between 20 and 90 degrees.

DRIFT/PULL
Pull is a tugging sensation, felt by the hands on the steering wheel, that must be overcome to keep the vehicle going straight.

Drift describes what a vehicle with this condition does with hands off the steering wheel.
^ A vehicle-related drift/pull, on a flat road, will cause a consistent deviation from the straight-ahead path and require constant steering input in the opposite direction to counteract the effect.
^ Drift/pull may be induced by conditions external to the vehicle (i.e., wind, road camber).

POOR GROOVE FEEL
Poor groove feel is characterized by little or no buildup of turning effort felt in the steering wheel as the wheel is rocked slowly left and right within very small turns around center or straight-ahead (under 20° of steering wheel turn). Efforts may be said to be "flat on center."
^ Under 20° of turn, most of the turning effort that builds up comes from the mesh of gear teeth in the steering gear. In this range, the steering wheel is not yet turned enough to feel the effort from the self-aligning forces at the road wheel or tire patch.
^ In the diagnosis of a roadability problem, it is important to understand the difference between wander and poor groove feel.