GMC 4000 Series Service Manual page 118

cylinder to tie rod "U" bolt nuts. With both tie rod
ends in same plane, tighten clamp bolts securely.
Refer to "Specifications" for correct toe-in.
On some vehicles with power steering, tighten
power cylinder to tie rod bracket "U" bolt nuts.
Adjust power cylinder as directed in "POWER
STEERING" (SEC. 9B) of this manual.
NOTE: Tie rod clamps must be lined up with
slots in tie rod tube or difficulty in tightening
clamps securely will be experienced.
FRONT WHEEL CAMBER
Camber is the amount in inches or degrees
that front wheels are tilted outward at top from
vertical position (see "C," fig. 1). Camber offsets
wheel deflection, due to wear of front axle parts,
and prevents a reverse or negative camber con­
dition. A reverse or negative camber is an inward
inclination of wheels at the top.
If camber is extreme or unequal between
wheels, improper steering and excessive tire wear
will result. Camber variations may be caused by
wear at wheel bearings and steering knuckle bush­
ings, or by a bent steering knuckle or axle center.
Specifications are listed at end of this section.
CHECKING AND CORRECTING CAMBER
Before checking camber, check wear at king
pins as follows:
Jack up front of vehicle, pull bottom of wheel
outward and take a camber reading; then pull top
of wheel outward and take a camber reading. If
readings vary more than 1/4 , make following
adjustments:
1. Adjust wheel bearings
"FRONT HUBS AND BEARINGS" (SEC. 3D), then
take camber readings as shown on Front End Align­
ment Chart (fig. 1). If readings still vary over 1/4°,
replace steering knuckle bushings and king pins
as instructed in "FRONT AXLE" (SEC. 3B).
2. Check the wheel run-out as instructed in
WHEELS AND TIRES (SEC. 10). If run-out is ex­
cessiv e, straighten or replace wheel.
3. Place vehicle on level surface, with normal
weight of vehicle on wheels, then take final camber
reading. If camber gauge is not available, readings
can be taken as shown on Front End Alignment
Chart in figure 1. Place square as shown and mea­
sure distances "A" and "B." "B" SHOULD EXCEED
"A" by amount specified. Camber dimensions of
right wheel should not vary over 3 /3 2" from cam­
ber dimensions of left wheel. If final camber read­
ing is incorrect, either steering knuckle or axle
center is bent.
4. To determine which part is bent, check king
pin inclination ("D," fig. 1). Camber plus king pin
inclination is the "included angle" of steering
knuckle. If "included angle" of knuckle varies more
than 1/2° from value specified in "Specifications,"
G M C S E R V I C E M A N U A L
knuckle is bent and should be replaced. Excessive
positive camber results in irregular wear of tires
at outer shoulder. Negative or reverse camber
causes wear at inner shoulder. Ease of steering is
affected by any deviation from specified camber.
vertical of the king pin. Negative or reverse caster
is the forward tilt from the vertical of the king pin.
springs, bent axle, twisted axle, or uneven tight­
ening of spring U-bolt nuts. Tighten all U-boltnuts
equally. Refer to "FRONT SPRINGS" (SEC 3C) for
U-bolt torque specifications. Generally, if the axle
is twisted, the caster will be unequal for right and
left side.
CHECKING AND CORRECTING CASTER
mensions are for vehicle carrying its design load
whereby the frame in most instances would be level.
If alignment check is to be made with frame NOT
LEVEL the frame angle (fig. 2) must be determin­
ed and added to the caster angle to obtain a true
caster reading.
frame angle (FA). See figure 2. Frame angle is
the degree of tilt in the frame from the level posi­
tion. Negative frame angle is when the frame is
high (above level) in the rear. Positive frame angle
is when the frame is low (below level) in the rear.
as directed in
wheel using the alignment equipment.
to the left wheel caster reading found in step 3 to
determine the "corrected caster" for left wheel.
frame and caster readings the following rules
apply:
FRONT END ALIGNMENT
AXLE CASTER
Positive caster is the rearward tilt from the
Incorrect caster may result from sagging
IMPORTANT: Caster, camber, and toe-in di­
1. Position vehicle on a smooth level surface.
2. Using a bubble protractor, measure the
3. Determine the caster angle for the left
4. Add the frame angle (FA) found in step 2
To determine "corrected caster" with various
(a) - Negative frame angle must be added to
positive caster reading.
(b) - Positive frame angle must be subtracted
from positive caster reading.
Sec. 3A
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