GMC 4000 Series Service Manual page 152

H e a A
Progressive type, two-stage rear springs, as
used on all 4000 and PS4500 Series (fig. 1), have
a straight-ended main leaf which rests against the
cam surface of the front and rear hangers, thereby
allowing the springs a full fore and aft float to
effect spring length changes. The second or third
leaf has hooked ends which contact rebound pins
in the spring hangers to prevent excessive fore
and aft travel in event of radius leaf rod failure.
The radius leaf rods maintain axle alignment
and transmit driving and braking forces to the
frame. A spacer is used at bottom of each spring
pile to separate the last leaf from the radius leaf
which is half-leaf formed with an eye and bushed
for attachment to the front hanger.
Two slanted U-bolts attach the spring pile and
radius leaf to the axle housing. Vari-rate type
rear springs shown in figure 2 are used on all "E,"
and "S" Series vehicles. The spring eye is bushed
and bolted to a bracket at front and is cam -sup­
ported at rear. Cam action of the spring leaf pro­
duces a variable deflection rate as contact point
changes under varying load.
NOTE: Refer to "Service Diagnosis Chart"
in "FRONT SPRINGS" (SEC. 3C) of this manual.
GENERAL SPRING MAINTENANCE
LUBRICATION
Spring leaves are lubricated at time of a s ­
sembly and require no further lubrication unless
spring is disassembled. Spring eye or radius leaf
G M C S E R V I C E M A N U A L
SECTION 4B
S i i
g m o
Figure J— Rear Springs Installed (Series 4 0 0 0 a n d P S4 50 0) (Typical)
I
bushings that are rubber-mounted do not require
lubrication.
TIGHTENING
At regular intervals, spring U-bolts should
be checked and tightened if necessary to torque
listed in "Specifications" at end of this section.
IMPORTANT: U-bolts must be kept TIGHT
at all tim es to hold axle inplace at springs. Other­
w ise, axle may shift, causing misalignment; also,
spring leaf failure in the vicinity of the spring
center bolt could result.
CAUTION
U-bolts must be retightened to initial
torque listed in "Specifications" after 500
m iles when new, or when spring repairs
are made.
NOTE: The center bolt serves only to hold the
spring together while in shipment and during in­
stallation, and as a locating point when assembling
spring to axle. After assem bly, it is strictly the
function of the U-bolts to hold the spring and axle
in alignment, and the importance of keeping the
U-bolts tight cannot be overemphasized.
REPAIR OPERATIONS
REAR SPRING REMOVAL (Figs. 1, 2, and 3)
1. Raise vehicle frame to take weight off the
spring. Make sure vehicle is supported safely.
Sec. 4B
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