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Chapter 26. Suspension Systems. Objectives (1 of 2). Identify and describe the types of suspension systems used on current trucks. List the components used on leaf and multi-leaf spring suspension systems and explain how they work. Describe a fiber composite spring.
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Chapter 26 Suspension Systems
Objectives (1 of 2) • Identify and describe the types of suspension systems used on current trucks. • List the components used on leaf and multi-leaf spring suspension systems and explain how they work. • Describe a fiber composite spring. • Identify equalizing beam suspension system components and explain how they function. • Identify torsion bar suspension system components and explain how they function.
Objectives (2 of 2) • Identify air spring suspension system components and explain how they function. • Troubleshoot suspensions and locate defective suspension system components. • Outline suspension system repair and replacement procedures. • Explain the relationship between axle alignment and suspension system alignment. • Perform full chassis suspension system alignments. • Describe the operation of the cab air suspension system.
Suspension Systems (1 of 2) • A suspension system plays a number of roles. • 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.
Suspension Systems (2 of 2) • Leaf spring • Equalizer beam • Leaf spring and solid rubber spring • Torsion bar • Air spring • Pneumatic-only and combination air/leaf spring
Suspension Terms • Jounce literally means “bump.” • In suspension terminology, it means the most compressed condition of a spring. For instance, many suspensions use jounce blocks to prevent frame-to-axle contact known as suspension slam. • Rebound is the reactive response of a spring after being jounced; it kicks back. • Unsprung weight, an important factor in a suspension, means the weight of any chassis components not supported by the suspension, for instance, the axles. • Ideally it is kept as low as possible because of the reaction effect, which is one of the reasons for spec’ing aluminum wheels. • Oscillation is either rhythmic or irregular vibrations or movements in a suspension. • For instance, a good suspension will minimize jounce/rebound oscillations by using dampening devices such as shock absorbers and multi leaf spring packs.
Leaf-spring Suspensions • A leaf spring is a steel plate or stack of clamped steel plates. • Most leaf springs used in trucks today are manufactured from spring steel. • Spring steel is middle-alloy steel that has been tempered, that is, heat-treated. • The result is to provide a leaf spring plate with considerable ability to flex without permanently deforming. • Leaf springs may consist of a single leaf or a series of leaves clamped together, known as a spring pack.
Self-dampening • The reason for using multiple leaves clamped together rather than a single piece of metal cut to the same shape has to do with what happens when a load is applied to the spring. • Interleaf friction • Interleaf friction provides a self-dampening characteristic to the spring pack. Two factors ensure a spring pack retains its self dampening. • First, when a spring pack is assembled, the individual leaves must never be lubricated or painted. This would reduce interleaf contact friction. • Second, the function of the center-bolt that clamps the leaves is critical. The tension it loads the leaves under helps define the self-dampening ability of the spring assembly. In the event of a broken center-bolt, much of the self- dampening properties of a spring pack are lost. • Shock absorbers not necessary • The advantage of the multi-leaf spring pack is that shock absorbers can be eliminated.
Shop Talk • When assembling multi-leaf spring packs, never paint or lubricate the contact surfaces of the individual leaves. • The result would limit the self-dampening characteristics of the spring.
Types of Leaf Spring Assemblies • Constant rate • Leaf-type spring assemblies that have a constant rate of deflection • Variable rate • Leaf-type spring assemblies with a variable deflection rate obtained by varying the effective length of the spring assembly
Leaf Spring Suspension Troubleshooting Guide • See Table 26–1 on page 810 of the textbook.
Rough Ride Diagnosis • See Table 26–2 on page 811 of the textbook.
Caution • When checking U-bolts, torque to the original specifications. • Rusty U-bolts should be disassembled, cleaned, and lubricated to ensure that the clamping pressure achieved by torquing is accurate.
Caution • Do not operate a vehicle with a shock absorber removed or defective because this places undue stress on other suspension components.
Shop Talk • Some shock absorber mount brackets have a stud welded to the bracket, rather than a nut and bolt. • This does not alter the installation procedure.
Caution • Failure to properly torque suspension fasteners can result in abnormal tire wear and damage to the springs, spring brackets, and frame rail.
Shop Talk • It is common practice to use SAE grade 8 fasteners in suspension systems but not universal. • Grade 5 bolts flex more than grade 8 bolts and that is required in some applications so replacing them with grade 8 fasteners is not appropriate. The body bound bolts with an interference-fit shank used by some OEMs are always grade 5. • When replacing suspension Huck™ fasteners with bolts, it is generally safe to use grade 8 bolts.
Caution • Failure to properly torque suspension fasteners can result in abnormal tire wear and damage to the springs, spring brackets, and frame rail.
Caution • You must apply Alumilastic™ compound, or an equivalent, to areas where aluminum and steel contact each other or the result will be metal corrosion and severely seized components.
Caution • It is not recommended to remove bushings by burning them out. • Once alight, they burn for a long time producing high heat and noxious fumes.
Caution • 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.
Summary (1 of 8) • A suspension supports the frame on a vehicle and acts as an intermediary between the axles and the frame. With no suspension, road forces would be transferred directly to the truck frame. • A suspension system plays a number of roles. • It stabilizes the vehicle over both smooth and rough terrain. • It cushions the chassis from road shock, enabling the driver to steer. • It maintains the proper axle spacing and alignment.
Summary (2 of 8) • There are four general categories of suspension used on trucks. • Leaf spring • Equalizer beam • Leaf spring and solid rubber spring • Torsion bar • Air spring • Pneumatic-only and combination air/leaf spring • Jounce describes a spring in its most compressed state, whereas rebound is a spring when it extends after reacting to jounce.
Summary (3 of 8) • Unsprung weight is the vehicle weight 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. • Constant rate and progressive or variable-rate springs are two types of leaf spring suspension used on trucks. • Auxiliary springs are helper springs and only become a factor when a vehicle is fully loaded.
Summary (4 of 8) • Steel springs are often assembled into semi-elliptical spring packs consisting of a stack of sprung steel plates clamped by a center-bolt. Spring packs are self-dampening because of interleaf friction. • Shock absorbers are used in suspension systems to dampen suspension oscillations. • Shock absorbers reduce tire wear, front wheel shimmy, and spring breakage.
