GMC 1982 Light Duty Truck Service Manual page 231

G overnm ental Periodic M otor Vehicle Inspection
programs usually include wheel alignment among items that
are inspected. To provide useful information for such
inspections, the specifications stated in column 2 of the
wheel alignment chart are given and these are well within
the range of safe vehicle operation.
In the event the actual settings are beyond the specifi­
cations set forth in column 1 or 2 (whichever is applicable),
or whenever for other reasons the alignment is being reset,
the specifications given in column 3 of the wheel alignment
chart should be used.
It is good practice to set front end alignm ent to
specifications while the vehicle is in its
condition. Trucks which are
heavy loads should have toe-in adjusted with the truck under
heavy load. This procedure should result in longer tire life.
ALIGNMENT ADJUSTMENTS
A normal shim pack will leave at least two (2) threads
of the bolt exposed beyond the nut. If two (2) threads cannot
be obtained, check for damaged control arms and related
parts. The difference between front and rear shim packs
must not exceed 7.62mm (.30 inches). Front shim pack must
be at least 2.54mm (.10 inches).
Access to Shim Packs
G 10-20 M odels, CIO M odels with 3 /4 " Nut:
With vehicle on front end rack, jack at frame and raise
the wheel off the ground. This will allow the upper control
arm to pivot down far enough to use a socket on the nuts and
permit shim removal.
G30 M odels, C 20 and 30 M odels with 7 /8 " Nut:
Remove the upper control arm bumper; then follow the
same procedure as above. Reinstall the upper control arm
bumper when alignment is completed.
normally loaded
con sisten tly operated with
P IV O T SHAFT O U T B O A R D O F FRAM E
CASTER
Fig. 3A-2-Caster - Camber Adjustment
Caster
All caster specifications are given assuming a frame
angle of zero. Therefore, it will be necessary to know the
angle of the frame (whether " u p " in rear or "down" in
rear) before a corrected caster reading can be determined.
Cam ber and toe can be read "as is" from the alignment
equipment.
H o w to D eterm ine Caster (Fig. 3A -4)
All caster specifications are given assuming vehicle
frame angle is zero. Therefore, it is necessary to adjust
specifications when applying them to vehicles with any
frame angle other than zero.
1. With vehicle on a level surface, determine frame angle
(whether up or down in rear) with the use of a bubble
protractor or inclinometer. Record this measurement
(See Figure 4).
2. Measure dimension " A " (See Figure 4).
3. Check and record specifications for caster under that
column related to dimension " A " as measured in step
.
2
4. Using one of the following rules, add or subtract frame
angle found in step 1 to or from specification found in
step 3.
a. A down-in-rear frame angle must be added to a
positive caster specification.
b. An up-in-rear frame angle must be subtracted from
a positive caster specification.
c. A down-in-rear frame angle must be subtracted from
a negative caster specification.
d. An up-in-rear frame angle must be added to a
negative caster specification.
Vehicle caster specification should be adjusted to
answer arrived at in step 4.
Camber
1. Determine the cam b er angle from the alignm ent
equipment.
2. Add or subtract shims from both the front and rear
bolts to affect a change.
CAMBER
FORW ARD
FRONT ALIGNMENT 3A-3