SHOCKS AND STRUTS
by Mark Davidson
STRUTS AND SHOCKS
Struts and shocks are used for ride control in the suspension system of a vehicle. They are designed to dampen the movement of the vehicle suspension as it reacts to changes in road surface. Shock absorbers are used with conventional coil spring, leaf spring or torsion bar suspension systems. Shocks serve to control the rebound action of the springs or torsion bars. Shock absorbers contain a large piston rod, hydraulic oil and a control valve. When the shock absorber compresses, the piston rod tries to force the hydraulic oil through an orifice in the control valve. The diameter of the orifice controls the stiffness of the shock absorber. A larger diameter orifice would provide a softer ride feel. Oil is drawn back into the piston area as the shock rebounds.
Gas charged shocks use nitrogen gas in a chamber above the hydraulic oil in the shock absorber. The action of the gas being compressed provides a more responsive shock absorber and a smoother ride. Macpherson struts are very similar to shock absorbers. In fact, they are basically large shock absorbers. The only difference is the Macpherson strut assembly also provides an anchor for the upper half of the vehicle suspension. Failure of shock absorbers can result in excessive tire bounce, excessive chassis bounce, uneven tire wear and wheel vibration or shimmy. Faulty shock absorbers can be revealed by a visual inspection for leaking fluid and worn bushings. A bounce test can be used to diagnose internal shock absorber failure. The bounce test is performed by rapidly pressing down the front or rear bumper of the vehicle and counting the number of times the vehicle bounces after it is released. The vehicle should not bounce more than three times after being released. Excessive bouncing would indicate internal leaking of the shock absorber. Macpherson strut diagnosis is similar to shock absorber diagnosis.
COIL AND LEAF SPRINGS
Both coil and leaf springs are used to provide support for the weight of the vehicle on the axles or suspension components. Coil springs are placed between the frame and the lower control arm. Leaf springs are mounted on the frame at each end and support the axle shaft in the center of the spring. A coil spring is constructed of a long metal rod rolled into a coil. The coil design provides excellent suspension travel when used in conjunction with a shock absorber for spring rebound control. The shock absorber is used to dampen the oscillations of the coil spring as it responds to variations in road surfaces. Leaf springs consist of a series of flat metal bars called leaves stacked upon each other. The longest section of the leaf spring attaches to the frame at each end. Leaves are stacked below the anchoring leaf and each lower leaf is correspondingly shorter than the next. A shock absorber is also used in conjuction with the leaf spring to dampen the oscillations of various road surfaces.
gave up on sports when the Browns left Cleveland and now spends his
Sundays working under a shade tree in the back yard tuning his son’s
soap box derby car.)