GMC 4000 Series Service Manual page 119

Sec. 3A
Page 112
FRONT END ALIGNMENT
(c) - Negative frame angle must be subtracted
from negative caster reading.
(d) - Positive frame angle must be added to
negative caster reading.
Example: L-4000 with power steering has a
left wheel caster reading of 2° posi­
tive, but the frame angle is negative
(high in the rear) 1/2°; therefore
1/2 ° negative frame angle plus 2°
positive caster gives 2V 2° positive as
the "corrected caster" for that wheel.
Referring to "Specifications," we
find that 2
over maximum specified setting.
5. Repeat steps 2 through 4for the right wheel.
6. If the caster is not within specifications,
caster can be corrected by adding or removing
caster shim s between the axle and spring.
IMPORTANT: Caster, camber, and toe-in dimensions 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 determined and added to the caster angle to obtain
a true caster reading.
NOTE: Use in Conjunction with Alignment Chart, Figure 1, page 110.
TRUCK MODELS
AXLE MODELS
B — M in us— A Cam ber ( I n c h e s ) ..
C — Cam ber (Degrees P o s it iv e )* .. .
D — King Pin Inclination (D e g re es).
E — M inus F —Toe-In (In ch e s)
C aster (D egrees P o s itiv e )* .............
K — M inus
( * ) N ote: When Power Steering is used, Standard or Optional Caster is the sam e as called out.
G M C S E R V I C E M A N U A L
y / P
positive caster is %°
FRONT END ALIGNMENT SPECIFICATIONS
L King Pin ( In c h e s ) .. .
—
KING PIN INCLINATION
King pin inclination is the amount that top of
king pin is inclined toward center of vehicle. King
pins are inclined ( D, fig. 1), to decrease friction
between tires and road when turning. Precision in­
struments must be used to check king pin inclin­
ation when axle is installed in vehicle. When axle
is removed, check can be made on bench as follows:
Place two uniform blocks on level surface,
rest spring seats on blocks. Using a square, mea­
sure "K" and "L" (fig. 1). "K" minus "L" equals
king pin inclination in inches. If axle is bent or
twisted, refer to "FRONT AXLE" (SEC. 3B) in
this manual for corrective information. Straighten­
ing axle center to correct king pin inclination will
also change camber. Recheck camber after cor­
recting king pin inclination.
E G /E M /E S -P S
4500 ALL 4000
E G / E M / E S /
SM/SG/SS5500
F050 F055
F-070
33/64 33/64
V l°
P/ ± P/ ± /4°
2 0 2 0
7-1/6 7-1/6
Vs - % V Vs -
k
W
23/4 l/2
a ± Vz
±
6% 4
51/ i4
E G / E M / E S /
S M /S G /S S /
5500
E M / E G / E S /
SM6500
F-070
33/64
1/2° + V l°
7-1/6
Vs Vi
-
23/4 ± 1 /2
63/64