Often, not much consideration is given to the venerable vehicle suspension and its important job of providing good ride, handling and control. This may sound like a simple task, but it is not. Many factors come into play that impact the suspension's proper operation.
Among the suspension's various functions: supports vertical loads - the vehicle's tare (empty) weight and when loaded; transfers loads from vehicle to ground via structural members, axles, wheels and tires; maintains axle and wheel position; provides compliance and isolation from road disturbances via springs and bushings for ride comfort and to maintain tire contact with the ground; and provides adequate stability and cornering stiffness for handling performance and safety. To do all this, the suspension must minimize frame movement and excitation, control vertical movement and lateral stiffness and provide damping to eliminate vibration and oscillation.
Because of the beating suspensions endure, components have a tendency to work themselves loose, tires can wear badly, springs can break, and so forth, causing increased repair costs, a loss of fuel economy and ride complaints from drivers among other things. Much of this can be avoided through proper and thorough suspension inspections and maintenance.
To get some guidance and advice on medium duty truck suspension care, Fleet Maintenance Magazine editor David A. Kolman turned to Hendrickson International, the leading supplier of truck, tractor, bus and recreational vehicle suspensions and springs; trailer suspensions, controls and non-integrated axles; truck and trailer lift axles; and bumpers and trim components.
In addition to performing a periodic visual inspection on applicable components per the manufacturer's specification, Hendrickson advises checking for:
• Tire wear : Inspect tires for wear patterns that may indicate suspension damage or misalignment. Replace all worn or damaged parts. Verify proper alignment and correct as necessary.
• Wear and damage: Inspect all parts of the suspension for wear and damage. Look for bent or cracked parts. Replace all worn or damaged parts.
• Fasteners : Look for any loose or damaged fasteners on the entire suspension. Make sure all fasteners are tightened to a torque value within the specified torque range. Use a calibrated torque wrench to check torque in the tightening direction. Replace any worn or damaged fasteners.
• Clamp group: Check torque on clamp group mounting hardware. Refer to the manufacturer's torque specifications.
• Air spring (if equipped): Inspect air springs for chafing or any signs of air spring or component damage. Check the overall condition of the upper and lower air spring brackets for dents, dings, cracks or other damage. Replace all worn or damaged parts.
• Steel leaf spring: Look for cracks. Replace if cracked or broken. Check the front bushing for any wear or deterioration and replace if necessary.
• Crossmember and gussets: Inspect the crossmember and gussets for any signs of loosening or damage. Inspect the bar pin clamp blocks for any signs of looseness or movement. Check all fasteners for proper torque. Replace all worn or damaged parts.
• Frame hanger: Inspect the frame hanger bracket for any signs of loosening or damage. Inspect all fasteners securing the frame hanger bracket to the frame rails, as well as the longitudinal torque rod mounting fasteners. Check all fasteners for proper torque. Replace all worn or damaged parts.
• Height control valve and air lines (if equipped): Check the suspension air system for air leaks. Check all air lines for proper routing and for chafing or pinched areas. Check the height control valve linkage for damage or interference with peripheral components. Replace all worn or damaged parts.
• Shock absorbers: Look for any signs of dents or leakage. Misting is not considered a leak. Misting is very small amounts of shock fluid that evaporate at a high operating temperature through the upper seal of the shock.
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Inspection guidelines for trailer air suspensions.