Front End Alignment Requirements; Alignment Adjustments - GMC G Service Manual

3A-4 FRONT END ALIGNMENT
FRONT END ALIGNMENT
REQUIREMENTS
Satisfactory vehicle operation may occur over a wide
range of front end alignment settings. If the settings vary
beyond certain tolerances, adjustments are advisable. The
"Specifications" at the back of this section is a guideline for
vehicle diagnosis or for repairs.
Set the front end alignment to specifications while the
vehicle is in its normally loaded condition. Vehicles which
are consistently operated with heavy loads should
have toe-in adjusted with the vehicle under heavy load.
This procedure should result in longer tire life.

ALIGNMENT ADJUSTMENTS

A normal shim pack will leave at least two threads of the
bolt exposed beyond the nut. If two threads cannot be
obtained, check for control arms and related parts. The
difference between front and rear shim packs must not
exceed 7.62 mm (0.30 inch). Front shim pack must be at
least 2.54 mm (0.10 inch).
A. Dimension " BC"
B. Jounce Bumper Bracket
C. Crossmember
D. A "DOWN IN REAR" frame angle must be SUB­
TRACTED from a POSITIVE caster reading.
CASTER ANGLE READING = + (2-1 /*°)
ACTUAL (CORRECTED) CASTER ANGLE = + (1°)
E. A "UP IN REAR" frame angle must be ADDED to a
POSITIVE caster reading.
CASTER ANGLE READING = + (2°)
ACTUAL (CORRECTED) CASTER ANGLE = + (3°)
ACCESS TO SHIM PACKS
Models with 3/4-Inch Nut
Jack up the frame to raise the wheel off the ground. This
will allow the proper upper control arm to drop down far
enough to use a socket on the nuts and permit shim adjust­
ment. Torque to specifications, refer to FRONT SUSPEN­
SION AND AXLE (SEC. 3C).
Models with 7/8-Inch Nut
Remove the upper control arm bumper; then follow the
same procedure as with 3/4-inch Nut. Torque to specifica­
tions. Reinstall the upper control arm bumper when align­
ment is completed. Refer to FRONT SUSPENSION AND
AXLE (SEC. 3C).
CASTER
All caster specifications are given with a frame angle of
zero. Therefore, it will be necessary to know the angle of
the frame (whether "up" in rear or "down" in rear) before a
corrected caster reading can be determined. Camber and
toe-in can be read "as is" from the alignment equipment.
HORIZONTAL
FRAME ANGLE = 1-1/4° DOWN
HORIZONTAL
FRAME ANGLE = 1° UP
Figure 2 — Determining Caster
B A
F. A "DOWN IN REAR" frame angle must be ADDED
to a NEGATIVE caster reading.
CASTER ANGLE READING = -
ACTUAL (CORRECTED) CASTER ANGLE = - (1-3/4°)
G. An "UP IN REAR" frame angle must be SUBTRACTED
from a NEGATIVE caster reading.
-CASTER ANGLE READING =
ACTUAL (CORRECTED) CASTER ANGLE = + (1°)
HORIZONTAL
r -
v FRAME ANGLE
\
= 1 /2° DOWN
o>=
H
HORIZONTAL
FRAME ANGLE
1 1 /«° UP
- ( / ° )
1 4
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