TRUCK SERVICE MANUAL
Outlined herein are Front Alignment Specifications pertaining to "Caster" "Camber" "Toe-In" and "King Pin Inclination".
Check alignment at regular intervals and particularly after front suspension has been subjected to extremely heavy service or
severe impact loads. Before checking and adjusting alignment, components such as wheel bearings, tie rods, steering gear, shock
absorbers and tire inflation should be inspected and corrected where necessary .
The caster, camber and toe-in settings are for unladen (no payload) vehicles.
King pin inclination is not required for any of the front end alignment checking machines as a means of obtaining caster or
camber. A check of king pin inclination can be used as an indicator of damaged king pins, knuckles or spindles.
Caster Measurement and Correction
Caster specifications are based on unladen (no payload) vehicles. If the frame is not level when alignment checks are made,
this must be considered in determining whether the caster setting is correct.
With the vehicle on a smooth, level surface, frame angle should be measured with a bubble protractor placed on the frame rail.
The degree of tilt from the level frame position is the angle that must be used in determining a correct caster setting. Positive frame
angle is defined as forward tilt (front end down) and negative angle as tilt to rear (front end high).
The measured frame angle should be added or subtracted, as required from the specified caster setting, to obtain the caster
that should actually be measured on vehicle .
Positive frame angle should be subtracted from specified setting.
Negative frame angle should be added to specified setting.
As an example, if the specified caster setting is a positive 1 deg. and it is found that the vehicle has a positive one degree
frame angle, then the measured caster should be 0 deg. 1/2 deg. caster angle when the chassis is operating under load .
Possible causes of incorrect caster are sagging springs, bent or twisted axle, or unequally tightened spring U-bolts. In most
cases a twisted axle would be the cause if caster varies more than the specified 1/2 deg. between left and right side.
If caster must be corrected, taper shims can be used as required between the springs and axle. Spring U-bolts should be
tightened evenly and to specified torque after the addition or removal of shims. Be sure spring center bolt drops into I-beam pilot.
Also, when tightening U-bolt nuts, be sure at least one full thread of U-bolt is visible when nut is tightened to specified torque. If not
visible, use longer U-bolt.
When U-Bolts are replaced, the new must be grade 5 minimum incorporating rolled threads.
U-bolt nuts are to be flanged head type or those having a nylon insert locking feature.
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