The chassis provides the structure that ties the suspension and steering components to the vehicle. The proper function of the chassis systems provides the driver with comfort, safety, and driving performance. Chassis systems have evolved to balance the requirements of improved comfort, more powerful engines, reduced vehicle mass, and improved safety.
Because these improvements have been so successful, vehicle operators can now detect minor disturbances and vibrations that would not have been apparent with previous vehicle generations. These slight disturbances can be challenging to diagnose. An experienced technician will understand the common symptoms for your make and model of vehicle and their causes. The team at Hollenshade’s Auto Service can help address these chassis dynamics issues effectively.
Components of a Typical Automotive Suspension System
Ball joints are used in the suspension system to allow relative movement between suspension components. The ball joint allows 3 degrees of rotational freedom and is commonly used in the front suspension to allow the wheel to move up and down (wheel travel), angle left and right for steering, and allow for relative fore/aft movement caused by deformation of bushings during braking and acceleration.
The design and shape of ball joints vary depending on the application. However, understanding the function of ball joints is important in diagnosis and repair. Ball joints serve two main functions: load carrying and following.
- A load carrying ball joint transfers axial and radial loads between the chassis to the wheel and tire. The load carrying ball joints are located on the suspension link that is connected to the spring. The load carrying ball joints may be under compression or tension when loaded.
- A follower or following ball joint locates the wheel and transfers radial loads from the chassis to the wheel and tire. The follower ball joint is located in control arms / links that are not connected to the spring or shock.
- RACK AND PINION: With the exception of some trucks and large vans, most vehicle steering systems are rack and pinion. The other linkage systems include parallelogram, cross-steer, and Haltenberger.
- PITMAN ARM: The pitman arm connects the steering linkage to the steering column through a gear located at the base of the steering column. The pitman arm transmits the motion it receives from the gear into the linkage, causing the linkage to move left or right to turn the wheels. There are two basic types of pitman arms: wear and non-wear. Wear arms have pivot studs and must be inspected periodically for wear. Non-wear arms have tapered holes at their center link ends and will need to be replaced only if they have been damaged or if the tapered hole is worn.
- IDLER ARMS: The idler arm is attached to the vehicle frame on the opposite side of the center link from the pitman arm. The pitman arm supports the center link at the correct height. A pivot built into the arm permits movement of the linkage. Because of this movement, wear usually is apparent at the swivel point of the arm.
- DRAG LINKS / CENTER LINKS: The purpose of drag links and center links is to control left and right linkage movement. The linkage movement changes wheel direction. Drag and center links are also mounting location for the tie rods and are important in maintaining toe settings. Center links with stud or bushing ends are likely to become worn from the effects of operation and should be inspected. Links with open tapers will only need to be replaced if they have been damaged or if the tapered hole is worn.
- TIE ROD ENDS: Tie rod ends are assemblies that connect the linkage to the steering arms and knuckles. Tie rod ends consist of: (1) inner tie rod ends. (2) Outer tie rod ends, which connect to the steering knuckles. (3) Adjusting sleeves or bolts, which join the inner and outer tie rod ends and permit the tie rod length to be adjusted. Tie rods are subject to accelerated wear and damage if the dust boots covering the ball stud are damaged or missing.
Shocks and Struts
Key components in the ride quality of a vehicle are the shocks and struts. Both are used to dampen or control the movement of the springs. If there were no dampening of the springs, the vehicle would bounce excessively and would be dangerous at high speeds. Dampening is the process of controlling the speed at which the spring is compressed and relaxed.
Shock absorbers control or dampen the movement of springs by using fluid or gas forced through holes in the shock absorbers’ pistons. As the shock absorber compresses or expands, a piston inside moves through oil or hydraulic fluid. The piston’s movement is resisted by the fluid, which must pass through small holes. If the holes are smaller, the shock absorber becomes stiffer, and delivers what is commonly known as a sportier ride with firmer handling characteristics. If the holes are bigger, the piston moves more easily and delivers a smoother ride.
Struts are a variation of the shock absorber with the additional function of supporting the vehicle. The coil spring is coaxially located on the strut. The coil spring sits on a spring perch within the strut housing. Two common types of strut suspensions are the MacPherson and the modified strut. MacPherson struts act as a locating member of the suspension.
Springs support the weight of the vehicle and absorb the shock of bumps and dips in the road surface. They make the ride more comfortable for passengers. There are several types of springs used in vehicle suspensions:
LONGITUDINAL LEAF SPRINGS
Longitudinal leaf springs absorb road shock and serve as axle locators. A centering pin is used to ensure that the axle is correctly located. Clips are used to hold the leaf bundle together, and U-bolts fasten the leaf bundle to the axle. The leaf spring is attached to the vehicle frame using a bolt and bushing assembly or a shackle assembly. If the spring is worn or damaged, other suspension components may shift from their proper positions. This shift in position causes increased wear-and-tear on the parts and impairs the vehicle’s handling. A damaged or missing centering pin adversely affects the vehicle’s alignment.
TRANSVERSE LEAF SPRINGS
Leaf springs may also be mounted transversely in some independent suspension systems. This configuration typically uses a single-leaf or mono-spring and may be manufactured using fiber composites instead of steel. A transversely mounted spring offers increased roll stability and requires a special unloading tool to service the spring or any related parts.
Unlike leaf springs, coil springs cannot control axle location; they only support the vehicle’s weight. Coil springs are constructed of a coiled steel bar and are located between the axle and the frame. Coil springs compress to absorb shock and then recoil to their correct height.
There are two types of coil springs: constant rate and variable rate. Constant rate coil springs provide even support throughout the range of travel. Variable rate springs have a variation in the number of coils per inch from one end to the other, which enables a vehicle to carry relatively heavy loads without sacrificing a comfortable ride in an unloaded condition. Under normal load, spring compression is minimal, which allows the vehicle to maintain a comfortable ride. When heavier loads are applied, the vehicle is able to maintain proper ride height as the dense coil-per-inch region of the spring is compressed.
TORSION BAR SPRINGS
Torsion bars are used in place of coil springs on some models and serve the same function. They are spring steel bars that are connected to the control arm on one end and anchored to the body or frame at the opposite end. They can be mounted to either control arm but are usually mounted to the lower arm. Instead of being set vertically on the vehicle, torsion bars run horizontally between a control arm and the frame. Lateral torsion bars run perpendicular to the vehicle centerline, whereas longitudinal torsion bars run parallel to the vehicle centerline.
The stabilizer bar, also known as a sway bar, is a metal rod running between the lower control arms. As the suspension at one wheel responds to the road surface, the stabilizer bar transfers a similar movement to the suspension at the other wheel. This provides a more level ride and reduces stabilizer (or lean) during cornering.
The stabilizer bar can be a one-piece, U-shaped rod fastened directly to the control arms with a bushing, or it can be attached to each control arm by a separate stabilizer bar link. Stabilizer bar bushings are a high-wear component and when degraded will cause excessive ‘knocking’ noise (especially on uneven pavement. And poor cornering when completely broken or disconnected. During maintenance services, the experienced technicians at Hollenshade’s will check the sway bar link bushings for wear.
Suspension Links and Bushings
The purpose of suspension links is to connect the various suspension joints with each other and to transfer forces and motion from one joint to the next. Ball joints or elastic bushings connect suspension links and other components. Suspension links are typically made from steel or aluminum and can have two, three, or four attachment points, depending on the design.
- CONTROL ARMS: Control arms control the movement of the wheel without supporting the vehicle’s weight.
- SUPPORT ARMS: Support arms transfer the spring and dampening forces from the vehicle body to the wheel.
- AUXILIARY LINKS: Auxiliary links are suspension links that connect support arms or control arms to one another or to the knuckle/wheel carrier. Auxiliary links alter the geometry through suspension travel in order to counteract geometry changes caused by acceleration and braking.
- BUSHINGS: Bushings are used in many places within the suspension system. Their main purpose is to absorb vibrations, and to provide a replaceable wear surface. PRO TIP: To prevent tearing of new bushings, tighten the links/arms at ride height.
Common replacement bushings are available for the following applications:
- King pin bushings
- Stabilizer bar bushings
- Stabilizer bar link kits
- Radius arm bushings
- Strut rod bushings
- Control arm bushings
Strut rods attach the control arm and frame on suspensions that use l-shaped lower control arms instead of A-shaped lower control arms. The shape allows the control arm a limited amount of forward and backward movement. Strut rods always attach toward the front of the frame, as opposed to a radius arm, which attaches toward the rear of the frame behind the tire. For certain vehicles, the Stabilizer bar serves as a strut rod. Bushings on the strut rod should be checked regularly, as they can wear out, which may cause:
- A pull to one side
- Excess tire wear
Hiper Strut: Design and Operation
The increasing power output of Front-Wheel Drive (FWD) vehicles increases the severity of torque steer symptoms. Torque steer is the undesirable feedback from the wheels to the steering system during acceleration. The driver will feel the vehicle pull hard to one side during hard acceleration. Various suspension designs incorporating additional control arms and links have been designed to reduce the negative impacts of torque steer. However, the additional links or control arms often lead to additional body structure changes and increasing costs.
To avoid this additional weight and cost, engineers tried to develop a suspension system that reduces torque steer and fits into the existing MacPherson body structure space. In theory, this type of system could be added to vehicles with a more powerful engine option without having to change the body structure used for the same model equipped with the base engine option.
The HiPer Strut (High Performance Strut) was the result of this GM development. One advantage of this system over the conventional MacPherson strut suspension is the reduced spindle length, which leads to:
- Reduced smooth road shake
- Less torque steer
- Increased tolerance of wheel imbalance
- Ability for larger tire fitment
- Reduced camber loss during cornering
- Increased cornering power / improved cornering linearity
- Premium steering feel
Multi-Link Independent Suspensions: Design and Operations
Multi-link independent suspensions address unwanted characteristics of older designs and to improve handling performance and comfort. They can be found in both the front and rear suspensions of many vehicles. The Cadillac CT6 front and rear suspensions are examples of multi-link independent suspensions. The CT6 front suspension has two lower links and a single upper link. The steering axis passes from the upper ball joint pivot through the imaginary intersection of the two lower links. This allows the steering axis to be oriented more vertically and closer to the wheel centerline. This also reduces the scrub radius with larger tires, reducing steering wheel feedback during acceleration and braking. The CT6 rear suspension has a 5-link independent rear suspension that uses an upper and lower lateral link, an upper and lower trailing link, and a toe adjust link to provide optimal handling and steering precision.
While the CT6 is just one example of the use of multi-link suspensions, there are many vehicles on the road that make use of multi-link suspension designs. The advantages of these systems are:
- Reduced unsprung weight
- Ability to tune the handling and geometry
- Reduces noise vibration and harshness transmitted into the passenger space
The disadvantages are typically increased cost and larger packaging within the vehicle chassis design. These more complex systems are found on higher-end vehicles.
Contact Hollenshade’s for Baltimore Car Repair & Maintenance Services
Hollenshade’s Auto Service is a leading provider of reliable, comprehensive auto repair and maintenance in Towson, MD. We offer the most competitive rates for transparent, ethical service. Contact us today to book your appointment.