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AUMT 1316 - Suspesion Systems 11/15/11

Steering and Suspension and Suspension

Suspension System Purpose

• The suspension system and frame must provide: Suspension Systems • steering control under all conditions • maintain proper tracking and directional Donald Jones stability Brookhaven College • a comfortable ride • proper alignment and minimize wear

Steering and Suspension Steering and Suspension

Jounce and Rebound Sprung and Un-Sprung Weight

• Jounce is the upward • Un-sprung weight movement or • and compression of • Wheel bearings and hubs suspension components • and steering knuckles • Rebound is the • Wheel mounted downward movement or components extension of suspension • Sprung weight components • Body and frame • Engine and • Load or cargo • Fuel

Steering and Suspension Steering and Suspension Center of Gravity

• 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 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 • Vehicle trim height seriously reduce the • riding height handling characteristics • Side-to-side lean of a vehicle

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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 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 the rear axle • Negative - rear • Negative - rear wheels point left wheels point left • Positive - rear wheels point right

Steering and Suspension Steering and Suspension

• 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

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Steering and Suspension Steering and Suspension 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 Absorbers

• Uniformly spaced coils • Control 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 Operation Shock Absorber Inspection

• Shock absorbers and • Visual inspection are used to • Oil film verses leakage control vehicle jounce • Bounce test and rebound • Push the down with considerable . 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

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Steering and Suspension Steering and Suspension MacPherson Struts MacPherson Service

• The strut mounts to • Strut bearing noise • Noise due to the knuckle/spindle insulator damage or at one end and to misalignment the 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 , 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 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 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 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 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 assembly

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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 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 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 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

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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 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 • control arm and • Coil spring frame • Strut • The shock attaches • Semi-Independent to the steering • Twist knuckle and pivots • Independent at the lower ball joint • MacPherson strut and upper strut bearing • Short over long arm

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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 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 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 Semi-Independent Independent Rear Strut

• A twist beam-type axle is • Each rear wheel can used to reduce jounce move independently and rebound transfer to from the opposite rear the other wheel as the wheel vehicle encounters road • Ride quality, tire life, imperfections steering control and • MacPherson struts are are improved are often used to support • Independent rear the vehicle’s weight, but suspension is used on an upper strut pivot FWD and RWD vehicles bearing is not required

Steering and Suspension Independent Rear SLA

• Rear SLA systems include an upper and lower control arm, a spring, and a shock absorber • The spindles are held in place with links, bars or arms since the tires are not normally used for steering

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