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LEAF SPRING SUSPENSIONS

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Suspension Systems
Objectives
• Identify the suspension systems used on current
trucks.
• Describe the components used on mechanical
leaf and multileaf spring suspension systems
and explain how they work.
• Identify equalizing beam suspension system
components and explain how they function.
• Identify air spring suspension system
components and explain how they function.
INTRODUCTION
A suspension system supports the frame on
a vehicle. It acts as an intermediary between
the axles and the frame. The axles are
subject to whatever forces they encounter
when running down the highway.
FUNCTIONS OF THE
SUSPENSION
• It stabilizes the truck when traveling over
smooth highway as well as over rough
terrain.
• It cushions the chassis from road shock
and enables the driver to steer the truck.
• It maintains the proper axle spacing and
alignment.
• It provides a smooth ride when both
loaded and unloaded.
• Jounce
Key Terms
– Most compressed condition of a spring
• Rebound
– Reactive response of a spring
• Unsprung Weight
– Weight of any chassis component not
supported by the suspension (keep low)
• Oscillation
– Rhythmic or irregular vibrations (shocks
prevent)
CATEGORIES OF SUSPENSIONS
• Leaf spring
• Equalizer beam: leaf spring and solid rubber
spring
• Rubber block and torsion bar
• Air spring: pneumatic-only and combination
air/leaf spring
LEAF SPRING SUSPENSIONS
(Constant Rate)
FRONT SUSPENSION
CONSTANT RATE
Example: 500lbs =1in
Rear Suspension—Single Axle
Shop Talk
When assembling multileaf spring packs,
never paint or lubricate the contact surfaces
of the individual leaves. The result would
severely limit the selfdampening
characteristics of the spring. (Interleaf
Friction)
The friction of the springs rubbing against
each other has a shock limiting effect.
Taper leaf spring assembly
Fewer leaves required=less weight
Variable spring rate, Front Axle
VARIABLE RATE
Overall length changes to carry increases loads
Axle Adjustments
FIBER COMPOSITE LEAF
SPRINGS
Used for a few years in autos, fiber composite
leaf springs have found their way into heavyduty trucks and trailers. They are made of
high-tech composite fibers that are laminated
and bonded by tough polyester resins. The
long strands of fiber are saturated with resin
and bundled together by wrapping (a process
called filament winding) or squeezed together
under pressure (compression molding).
Maintenance
U-bolts that loosen in service place undue
strain on the spring center bolt. OEMs state
that center bolts should be re-torqued at
specified intervals but this is seldom done. If
you are torquing center bolts on a spring not
clamped by U-bolts, remember that they are
under considerable tension should the center
bolt fail.
SPRING SUSPENSION WITH
SHOCK ABSORBERS
Shock Absorber Inspection
OEMs suggest checking shock absorbers at
intervals of 12,000 miles (20,000 km).
Do not operate a vehicle with a shock
absorber removed or defective because this
places undue stress on other suspension
components.
Rear Suspension—Tandem Axle
Torque Rod
EQUALIZER REPLACEMENT
Bogie Suspensions
A bogie is a general term used to describe a
pair of axles arranged with common
suspension members designed to act and
react together. The ends of both camelback
spring assemblies and walking beams are
mounted in rubber shock insulators.
EQUALIZING BEAM
SUSPENSIONS
Two types of equalizing suspensions are
used on heavy-duty trucks:
• Leaf spring type
• Solid rubber or rubber cushion type
-Allow maximum suspension travel
LEAF SPRING EQUALIZING BEAM
CUSHION AND TORSION
SUSPENSIONS
Sectional view of the rubber cushiontype equalizing beam suspension.
CONTROL LINK, RUBBER SPRING
AND EQUALIZING BEAM
One variable rate rubber spring located in the center of the tandem
8 links to align axles
SERVICING EQUALIZING
BEAMS
Power wash the suspension and inspect the
components for cracks or damage. Inspect
rubber bushings for damage or deterioration
and plan to replace them if they show any
indications of fatigue.
There are 3 types:
EQUALIZING BEAM OVERHAUL
Tube-type beam end mounting
Ball and socket beam end
mounting.
AIR SPRING SUSPENSIONS
Combination air/steel spring
suspension installation
AIR AND TORSION ROD SUSPENSION
Kenworth: max travel best ride
Air Springs
AIR SPRING TERMINOLOGY
SHOCK ABSORBER
ORIENTATION
RIDE HEIGHT ADJUSTMENT
Location of the height control valve
and components.
CHECKING A RIDE HEIGHT
CONTROL VALVE
Most ride height control valves have a
reaction delay that can be as long as 15
seconds. This is used to prevent continuous
correction cycling. Remember this when
diagnosing height control valve problems.
A simple test is to remove the control rod and
manually raise and or lower the frame height.
REPLACING A HEIGHT
CONTROL VALVE
AIR CIRCUIT MAINTENANCE
AXLE ALIGNMENT
Several types of equipment and methods can
be used to check axle alignment. These
methods include light and laser beam
alignment equipment and computer controlled
sensor systems. A straightedge and trammel
can also be used to check axle alignment.
This last method is the most difficult and
inaccurate method of checking axle alignment
and should be used only when no other
alignment equipment is available.
Laser Alignment
Tram bar
Measuring dimension “A” axle
alignment.
Cab air suspension system with a
transverse rod, two air springs, one shock
absorber and a leveling valve.
Exploded view of two-point cab air
suspension.
DRIVER SEATS
Air-suspended driver’s
seat
Solid-mounted seat.
Summary
There are four general categories of
suspension used on trucks:
• Leaf spring
• Equalizer beam: leaf spring and solid
rubber spring
• Rubber or air cushion cushion and torsion
bar
• Air spring: pneumatic-only and
combination air/leaf spring
Summary (cont.)
• Jounce describes a spring in its most
compressed state, whereas rebound
describes a spring when it extends after
reacting to jounce.
• Unsprung weight is not supported by the
suspension; it includes the wheel and axle
assemblies. Because unsprung weight
reacts directly through the suspension to the
frame, it is kept as light as possible.
Summary (cont.)
• Shock absorbers are used in suspension
systems to dampen suspension
oscillations. Shock absorbers reduce tire
wear, front wheel shimmy, and spring
breakage.
• Air bags can be either the reversible sleeve
type or the convoluted type.
Summary (cont.)
• Air springs have no self-dampening
capability so they almost always use shock
absorbers.
• Equalizer beam suspensions are used in
tandem drive and bogie arrangements to
effectively balance suspension stresses
and maximize tire-to road contact.
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