GMC 4000 Series Service Manual page 124

DESCRIPTION
Front springs on all series are vari-rate leaf
type. Springs are attached to front axle center with
U-bolts and secured at frame side rails as shown
in figure 1. U-bolts may also secure shock ab­
sorbers and tow eyes (when used). Spring eyes
on all series are equipped with replaceable bush­
ings. The front spring rear hangers on some ve­
hicles have a floating cushion. The cushion is held
in place by the front spring rear hanger rebound
bolt, and can be reversed to extend wear life of
spring end-to-cushion metal contact area. Refer
to figure 1. Front springs which employ rubber-
mounted bushings with solid eye bolt, require no
lubrication at bushing.
GENERAL SPRING MAINTENANCE
LUBRICATION
Spring leaves are lubricated at time of a s­
sembly and require no further lubrication unless
spring is disassembled.
TIGHTENING
IMPORTANT: U-bolt nuts must be retightened
to initial torque listed in "Specifications" at end of
this section, after 500 m iles. Thereafter, U-bolts
should be checked at regular intervals. U-bolts
must be kept TIGHT at all tim es to hold axle in
place at springs. Otherwise, axle may shift, caus­
ing misalignment; also, spring leaf failure in the
vicinity of the spring center bolt could result.
The center bolt serves only to hold the spring
together while in shipment and during installation,
and as a locating point when assembling spring to
axle. After assembly, it is strictly the function of
the U-bolts to hold the spring and axle in align­
CONDITION
Spring Noise
Spring Sag or
Bottom
Spring Breakage
G M C S E R V I C E M A N U A L
SECTION 3C
f y n c - n t
SERVICE DIAGNOSIS CHART
POSSIBLE CAUSE
1. Loose U-bolts.
2. Loose or worn shackle bushings.
3. Lack of lubrication.
4. Defective shock absorber.
1. Inoperative shock absorbers.
2. Broken spring leaf.
3. Severe operation or overloading.
1. Loose U-bolts.
2. Normal fatigue.
3. Overloading.
ment, and the importance of keeping the U-bolts
tight, cannot be overemphasized.
Check, and tighten if necessary, all spring
bracket bolt nuts and bracket pin clamp bolts. Re­
bound clips should be tightened just enough to hold
spring leaves in alignment without restricting free
movement of leaves.
REPAIR OPERATIONS
FRONT SPRING REMOVAL (Refer to Fig. 1)
1. Raise vehicle frame to take weight off the
spring. Make sure vehicle is supported safely.
2. Support axle on floor jack.
3. Remove spring shackle U-bolt nuts, then
lower axle.
4. At front of vehicle, remove spring eye bolt,
nut, and washer; withdraw eye bolt from bracket
and spring eye.
5. On all L-4000 Series, remove bolt, bolt
retainer, and rebound pin at rear hanger. On all
"E," "S ," and "PS" Series, remove nut, lockwash-
er, rebound bolt, and spacer at rear hanger.
6. Remove shock absorber bracket (if used)
(figs. 2 and 3), spring caster spacer, tow eye (if
used) and dowel pins (when used). Also, front
spring rear hanger cushion (when used). Remove
spring.
NOTE: Refer to figures 2 and 3 for correct
position of caster spacer at time of installation.
INSPECTION
1. Thoroughly clean spring eye bushings, bolts,
and pins.
2. Insert bolts or pins into bushings in spring
eyes, and check for looseness. If excessive lo ose­
ness is evident, bolt pin or bushing must be re­
placed.
CORRECTION
1. Tighten to recommended torque.
2. Replace shackle bushings.
3. Lubricate as required.
4. Replace shock absorber.
1. Replace shock absorbers.
2. Replace leaf or spring assy.
3. Check load capacity rating.
1. Tighten to recommended torque.
2. Replace spring.
3. Check load capacity rating.
Sec. 3C
Page 117