Suspension Systems Suspension Systems A suspension system plays

Suspension Systems

Suspension Systems 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 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.

Spring Pack Principles

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 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

Progressive Spring Operation

Multi-leaf Shackle Spring

Single Drive Axle Spring Suspension

Tandem Axle, Equalizer Spring Suspension System

Semi-elliptical Springs with Shocks

Equalizing Beam Suspension System Leaf Spring-type

Equalizing Beams with Rubber Cushions

Leaf and Air Suspension System

Leaf and Air Suspension System

Height Control Valve

Air Springs

Leaf Spring Suspension Troubleshooting Guide

Rough Ride Diagnosis

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.

Torque Rod Disassembly

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.

Height Control Valve Centering Pin

Air Spring Replacement

Air Plumbing Diagram