Suspension Systems Objectives вЂў Identify the suspension systems used on current trucks. вЂў Describe the components used on mechanical leaf and multileaf spring suspension systems and explain how they work. вЂў Identify equalizing beam suspension system components and explain how they function. вЂў 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 вЂў It stabilizes the truck when traveling over smooth highway as well as over rough terrain. вЂў It cushions the chassis from road shock and enables the driver to steer the truck. вЂў It maintains the proper axle spacing and alignment. вЂў It provides a smooth ride when both loaded and unloaded. вЂў Jounce Key Terms вЂ“ Most compressed condition of a spring вЂў Rebound вЂ“ Reactive response of a spring вЂў Unsprung Weight вЂ“ Weight of any chassis component not supported by the suspension (keep low) вЂў Oscillation вЂ“ Rhythmic or irregular vibrations (shocks prevent) CATEGORIES OF SUSPENSIONS вЂў Leaf spring вЂў Equalizer beam: leaf spring and solid rubber spring вЂў Rubber block and torsion bar вЂў Air spring: pneumatic-only and combination air/leaf spring LEAF SPRING SUSPENSIONS (Constant Rate) FRONT SUSPENSION CONSTANT RATE Example: 500lbs =1in Rear SuspensionвЂ”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 SuspensionвЂ”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: вЂў Leaf spring type вЂў 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 вЂњAвЂќ 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 driverвЂ™s seat Solid-mounted seat. Summary There are four general categories of suspension used on trucks: вЂў Leaf spring вЂў Equalizer beam: leaf spring and solid rubber spring вЂў Rubber or air cushion cushion and torsion bar вЂў Air spring: pneumatic-only and combination air/leaf spring Summary (cont.) вЂў Jounce describes a spring in its most compressed state, whereas rebound describes a spring when it extends after reacting to jounce. вЂў 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.) вЂў Shock absorbers are used in suspension systems to dampen suspension oscillations. Shock absorbers reduce tire wear, front wheel shimmy, and spring breakage. вЂў Air bags can be either the reversible sleeve type or the convoluted type. Summary (cont.) вЂў Air springs have no self-dampening capability so they almost always use shock absorbers. вЂў Equalizer beam suspensions are used in tandem drive and bogie arrangements to effectively balance suspension stresses and maximize tire-to road contact.