AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Suspension System Purpose • The suspension system and frame must provide: • steering control under all Suspension Systems road conditions • maintain proper vehicle tracking and directional Donald Jones stability Brookhaven College • a comfortable ride • proper wheel alignment and minimize tire wear Steering and Suspension Steering and Suspension Jounce and Rebound Sprung and Un-Sprung Weight • Jounce is the upward • Un-sprung weight movement or • Wheels and tires compression of • Wheel bearings and hubs suspension components • Axles and steering knuckles • Rebound is the • Wheel mounted brake downward movement or components extension of suspension • Sprung weight components • Body and frame • Engine and transmission • Load or cargo • Fuel tank Steering and Suspension Steering and Suspension Center of Gravity Ride Height • The point around which • Ride height is the height at which a vehicle’s sprung the vehicle’s weight is components are carried over centered the vehicle’s un-sprung Center of components • As weight distribution is Gravity • Ride height is a suspension altered, the CG is measurement taken from un- moved sprung to sprung components • Excessive sprung • Vehicle ride height is not the weight loaded higher same as: than the CG will • Vehicle trim height seriously reduce the • Curb riding height handling characteristics • Side-to-side lean of a vehicle 1 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Vehicle Trim Height Setback • Side-to-side lean is a term used to describe • Setback is a reference the difference in the height of the vehicle to the difference in side- body usually measured from a point on the to-side wheelbase body to the ground on both sides of the • Positive Setback vehicle • The RH wheelbase is longer, using the left side as a base • Negative Setback • The RH wheelbase is shorter, using the left side as a base Steering and Suspension Steering and Suspension Thrust Angle Thrust Angle • Angle between the • Angle between the vehicle's centerline vehicle's centerline and the thrust-line of and the thrust-line of the rear axle the rear axle • Negative - rear • Negative - rear wheels point left wheels point left • Positive - rear wheels point right Steering and Suspension Steering and Suspension Caster Angle Camber Angle • Forward or rearward • Inward or outward inclination of the tilt of the wheel and steering axis tire when viewed from the front of the • Directional control vehicle angle • Directional control • vehicle will pull to the angle least positive side • vehicle will pull to the • Not a tire wear angle most positive side • Tire wear angle 2 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Toe Angle Springs • Inward or outward • Springs support the variation of tires vehicle’s weight from a straight located above the ahead position springs • Toe In vs. Toe Out • Coil springs • Not a directional • Leaf springs control angle • Torsion bars • Tire wear angle • Air springs Steering and Suspension Steering and Suspension Coil Springs Types Shock Absorbers • Uniformly spaced coils • Control spring provide a linear compression rate oscillation and • Variable rate springs rebound provide a comfortable • Reduce body sway ride with increased and lean on turns loading capacities • Variable rate coil • Reduce the springs are normally tendency of a tire to installed with the tight lift off the road coils up as shown here Steering and Suspension Steering and Suspension Shock Absorber Operation Shock Absorber Inspection • Shock absorbers and • Visual inspection struts are used to • Oil film verses leakage control vehicle jounce • Bounce test and rebound • Push the bumper down with considerable force. One • Shock absorbers are upward free bounce should double acting stop the vehicle motion • Ratios are expressed as • Manual test extension/compression • A shock absorber should • Ratios from 50/50 to offer steady resistance for 80/20 are available the entire rebound and compression stroke • A ratio of 70/30 is common 3 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension MacPherson Struts MacPherson Strut Service • The strut mounts to • Strut bearing noise • Noise due to coil spring the knuckle/spindle insulator damage or at one end and to misalignment the chassis or body • Noise due to coil spring at the other end interference with the upper rebound stop, strut tower or • On front suspension strut mount assembly systems the upper • Some strut cartridges are replaced on car, but most end of the strut require the strut and spring assembly rotates in assembly be removed from the strut bearings the vehicle for service Steering and Suspension Steering and Suspension Strut Service Precautions King Pins • Always use a coil spring compressing tool according to the • King pins may be used tool or vehicle manufacturer’s recommended service as steering pivot points procedure. on vehicles with solid • Be sure the tool is properly installed on the spring. front axles or twin I- • Never loosen the upper strut mount retaining nut on the beam suspension end of the strut rod unless all spring tension is removed systems from the upper strut mount. • Large steel or fiber pins • Never clamp the strut or shock absorber in a vice with fit into eyes in the excessive force. steering knuckle and • If the coil spring has an enamel-type or plastic coating and into a hole in each end the compressing tool damages the finish it may lead to of the axle premature spring failure. Steering and Suspension Steering and Suspension Ball Joints Ball Joint Service • Ball joints are the • Ball joint failures pivot points that • Noise • Excessive steering effort allow the spindles or • Poor steering return ability steering knuckles to • Ball joints inspection turn • Wear indicators • Travel • Load carrying • Articulation effort • Non-load carrying • Ball joints are often serviced as a control arm assembly 4 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Control Arms Bushings • Control arms allow the • Bushings are used suspension to move up to provide a firm yet and down in response flexible mounting to irregularities in the road surface point for suspension • They are attached to components the chassis with • Bushings should be bushings and to the inspected for knuckle/spindle with ball deterioration and/or joints or bushings damage Steering and Suspension Steering and Suspension Stabilizer Bars Suspension Inspection • The stabilizer bar helps to • Spring condition control body roll on turns • The stabilizer bar is attached • Shock absorbers to the suspension members • Control arms on each side of the vehicle and to the chassis with • Sway bars bushings • The spring steel bar resists • Links, arms, etc. twisting and forces the • Bushings vehicle to shift its weight back into the turn, instead of • Ride height away from it Steering and Suspension Steering and Suspension Front Suspension Types Solid Front Axle • Solid Front axle • Solid front axles deliver a high load • Twin I-beam capacity at the • Short over long expense of driving arm comfort and • Torsion bar performance • The axles may be • MacPherson strut driven or non-driven • Modified and commonly use MacPherson strut leaf style springs 5 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Twin I-Beam Short Over Long Arm • I-beams are mounted to • Two control arms are pivot points on the opposite attached to the frame side of the vehicle • During jounce and • Coil springs support the rebound the two length vehicle’s weight between the control arms move the I-beam and the frame tire through an arc • Radius arms control lateral maintaining the tire to and torsional movement of road alignment the I-beams • Provides good load capacity • Reduced tire wear, and vehicle ride improved ride quality characteristics and directional control Steering and Suspension Steering and Suspension Torsion Bar MacPherson Strut • Torsion bars are spring • The spring and steel bars mounted to the control arm and the frame shock are combined of the vehicle to form the strut • The torsion bar is the only assembly spring that is manually • The steering knuckle adjustable to correct ride height and strut pivot at the • Torsion bars are marked lower ball-joint and right and left, and must be the upper strut installed on the correct bearing side of the vehicle • Compact design Steering and Suspension Steering and Suspension Modified MacPherson Strut Rear Suspension Types • The coil spring is • Rigid rear axle located between the • Leaf spring control arm and • Coil spring frame • Strut • The shock attaches • Semi-Independent to the steering • Twist beam axle knuckle and pivots • Independent at the lower ball joint • MacPherson strut and upper strut bearing • Short over long arm 6 AUMT 1316 - Suspesion Systems 11/15/11 Steering and Suspension Steering and Suspension Leaf Spring Coil Spring • Leaf springs can • Coil springs require support large amounts links, bars, struts or of sprung vehicle weight arms to control fore, aft and lateral movement of • Leaf springs also the axle provide excellent fore, • Commonly used in aft and lateral control of RWD cars where the axle compact design and • Materials other than ride quality are more steel have been used important that load leaf spring production capacity Steering and Suspension Steering and Suspension