GMC 1986 P-Truck Service Manual page 181

3A-4 FRONT END ALIGNMENT
A.
Camber
B.
Add shims here to increase caster
C.
Figure 2—Caster - Camber Adjustm ent Pivot Shaft Outboard Of Frame
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 (0.03 inch). Front shim pack must
be at least 2.54 mm (0.10 inch).
ACESS TO SHIM PACKS
Models w ith 3/4-lnch 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 adjustment. Torque to specifications, refer
to FRONT SUSPENSION (SEC. 3C).
Models with 7/s-lnch Nut
Remove the upper control arm bumper; then follow
the same procedure as with 3/4-inch Nut. Torque to
specifications. Reinstall the upper control arm bumper
when alignm ent is com pleted. Refer to FRONT
SUSPENSION (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.
How To Determine Caster (Figure 2 and 3)
All caster specifications are given with vehicle frame
angle of zero.
1. Position the vehicle on a smooth level surface.
2. Use a bubble protractor or inclinom eter to
measure the frame angle. Frame angle is the
degree of tilt in the frame from the level position.
Subtract shims here to increase caster
E.
F.
Add shims equally to increase camber
3. Determine whether the frame angle is " up in
rear" or " down in rear."
4. Determine the caster angle reading from the
alignment equipment.
5. Refer to figure 3. To determine an " actual
(corrected) caster reading" with various frame
angles and caster readings, one of the following
rules apply:
a. A " DOWN IN REAR" frame angle must be
SUBTRACTED from a POSITIVE caster
reading.
b. An " UP IN REAR"
ADDED to a POSITIVE caster reading.
c. A " DOWN IN REAR" frame angle must be
ADDED to a NEGATIVE caster reading.
d. An " UP IN REAR" frame angle must be
SUBTRACTED from a NEGATIVE caster
reading.
6. Dimension " BC" measured 90 degrees from the
lower surface of the crossmember (C) and to the
inboard rear corner of the jounce bumper bracket
(B).
7. Using dimension " BC" and the caster, camber,
wheel toe-in chart sheet, find the recommended
caster angle.
8. If the actual (corrected) caster cycle (Step 5) is
not within the recommended caster angle (Step
7) make the necessary shim changes.
CAMBER
1. Determine the camber angle from the alignment
equipment.
2. Add or subtract shims from both the front and
rear bolts to affect a change.
B-07372
fram e angle m ust be