Contour Enthusiasts Group Archives Forums Modifications Suspension Control Arm Assembly?

Can you tell from this picture if I have the Horizontal or Vertical? I am going to order from BAT but would like to make sure i get the right one.

Thanks.

Can't tell by the picture, but if you go to the "Bat Inc" web site they show a picture of the vertical type under their suspension products.

Can't really tell from your pick but here is my SVT E0 Lower control arm (Horizontal).

PS. Your looking at the driver side front control arm with the wheel turned to the left.



Hope that helps. Let me know if you need more pics.

Originally posted by Tony D:

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Can you tell from this picture if I have the Horizontal or Vertical? I am going to order from BAT but would like to make sure i get the right one.

Thanks.

---

Take a picture of the arm below the boot in your picture.

my g/f took my camera to the UK with her. She'll be back in 10 days. I'll repost then.

Thanks guys

SHOCKS & STRUTS 101


Shocks and struts are safety components that maintain vertical loads placed upon tires to help keep the tires in contact with the road.

Shocks do not support the weight of the vehicle, they are major components of the suspension system and control suspension movement.

Struts are a major structural member of the suspension system since they provide structural support for the vehicle's suspension. Like shocks, they also control suspension movement.

Shocks and struts are two-way Velocity Sensitive Hydraulic Damping Devices--the faster they move, the more resistance they have.

New Monroe® Shocks and Struts Help...

Keep the tire in contact with the road by controlling spring and suspension movement.
Control vehicle bounce, roll and sway, dive, acceleration squat
The Benefit of replacing Worn Shocks and Struts...

Help reduce wear on other suspension components
Help maintain dynamic wheel alignment
Help prevent premature tire wear over a period of time
Help provide consistent control for improved handling and braking performance

A Brief History


Early vehicle manufacturers began finding solutions to the problems of steering and passenger comfort. The front wheels were attached to the axle using steering spindles and kingpins, which allowed the wheels to pivot while the axle remained stationary. And the up and down oscillations of the leaf springs were damped by a device called a "shock absorber."

These first shock absorbers were simply two arms connected by a bolt, with a friction disc between them. Resistance was adjusted by tightening or loosening the bolt. As might be expected, these shocks were not very durable. And their performance left much to be desired.

Over the years, suspension systems evolved into sophisticated design. Concepts and components have changed -- and continue to change -- dramatically. But, the basic objectives remain the same:

To provide steering stability with good handling characteristics, and
To maximize passenger comfort.
Achieving these objectives under all the variables of a vehicle in motion is what we call ride control.



Ride control is affected by the weight of the vehicle, the weight distribution, vehicle speed, road conditions and the condition of suspension system components, including tires, and wheel alignment. It's the job of the Ride Control Expert to make sure the suspension components are in good shape and the wheels are properly aligned. After doing that job, the effects of the other variables will be minimized. The car or light truck will steer and handle well, and the passengers will ride in comfort over the full range of driving conditions.

As we review suspension system components and how they work together, remember that a vehicle in motion is much more than wheels turning. As the tire revolves, the suspension system is in a dynamic state of balance, continuously compensating and adjusting for changing driving conditions. The modern suspension system is automotive engineering at its best.

Suspension Systems: The Basics
To begin this training program, you need to know some basic information. First, you should know that the tires and wheels make vehicle motion possible. The chassis connects the tires and wheels to the vehicle's body. The chassis consists of the frame, suspension system, steering system, tires and wheels.



When discussing a vehicle's chassis, the side-to-side distance between the centerline of the tires on an axle is called track. The distance between the center of the front and rear tires is called wheelbase. If the vehicle is in proper alignment, the wheels will roll in a line that is parallel with the vehicle's geometric centerline.

Vehicle geometry, suspension, and steering design all affect the "handling" of a vehicle. To better understand the term handling, we can address the following fundamentals that contribute to good handling:

ROAD ISOLATION is the vehicle's ability to absorb or isolate road shock from the passenger compartment.

DIRECTIONAL STABILITY is the ability of the vehicle to maintain a directed path.

RETURNABILITY is the ability of the vehicle to return the front wheels to straight ahead after turning.

TRACKING is the path taken by the front and rear wheels.

CORNERING is the ability of the vehicle to travel a curved path.

So, to a great extent, handling depends on optimizing the vehicle's suspension dynamics, or dynamic control. This means that when a vehicle is in motion, all the components in the suspension system work together effectively to provide tire-to-road contact. The amount of this traction force between the tires and the road is the major factor in how well a vehicle can maneuver through corners, or as it stops and accelerates.

The components of the suspension system perform five basic functions:

Maintain correct vehicle ride height
Reduce the effect of shock forces
Maintain correct wheel alignment
Support vehicle weight
Keep the tires in contact with the road
Control the vehicle's direction of travel.
However, in order for this to happen, all of the suspension components, both front and rear, must be in good working condition.

Suspension Systems: Comfort and Safety


The suspension system allows the vehicle body to ride relatively undisturbed while traveling over rough roads. It also allows the vehicle to corner with minimum roll or sway, stop with a minimum of brake dive, and accelerate with a minimum of acceleration squat. This dynamic control will keep the tires in contact with the road.

Shocks and Struts ARE Safety Equipment
Most people believe that shocks and struts are only necessary for improving a vehicle's riding comfort and handling. In truth, they do much more than that; their job is to help keep tires on the road. A vehicle riding on worn shocks and struts may be unsafe not only to the driver and passengers, but also to other vehicles on the road. By replacing your worn shocks and struts, you're providing yourself with a safer, more secure vehicle.

Tire Force Variation: "Downward Force on Tires"


It's important to understand that a vehicle's ability to steer, brake and accelerate depends first and foremost on the adhesion, or friction, between the tires and the road. This adhesion is also referred to as the roadholding capability of the vehicle.

"Tire Force Variation" is a measure of the roadholding capability of the vehicle, and is directly influenced by shock absorber or strut performance. Shock absorbers and struts help maintain vertical loads placed on the tires by providing resistance to vehicle bounce, roll and sway. They also help reduce brake dive along with acceleration squat to achieve a balanced ride. Worn shocks and struts can allow excessive vehicle weight transfer from side to side and front to rear...and that reduces the tire's ability to grip the road. Because of this variation in tire-to-road contact, a vehicle's handling and braking performance can be reduced. This may affect the safe operation of the vehicle and the safety of those riding inside. Therefore, shocks and struts ARE SAFETY COMPONENTS.







WHAT CONTROLS TIRE FORCE ARE THE SHOCKS OR STRUTS ON THAT VEHICLE!
Tire loading changes as a vehicle accelerates, decelerates, and turns corners; the size of the four circles of traction at the tires is also changing with the changes in tire load. As a vehicle turns a corner, centrifugal force causes weight to transfer from the tires on the inside of the turn to the tires on the outside. As a vehicle brakes, inertia will cause weight to transfer from the rear tires to the front tires; weight will transfer from the front to the back during acceleration.

Suspension Systems: Main Components


At this point it's easy to understand that the main components of a moving vehicle's suspension system are the struts, shock absorbers, springs, and tires. Struts are a major structural member, while shock absorbers are a major component. The struts and shock absorbers control, or damp, excessive spring and suspension movement.

The springs support the weight of the vehicle, maintain ride height, and absorb road shock. Springs are the flexible link that allows the frame and body to ride relatively undisturbed while the tires and suspension follow the bumps in the road.

Springs are the compressible link between the frame and the body. When additional load is placed on the springs, or the vehicle meets a bump in the road, the springs will absorb the load by compressing. The springs are a very important component of the suspension system that provides ride comfort. Shocks and struts help control how fast the suspension is allowed to move which is important in keeping the tires in firm contact with the road.

During the study of springs, the term bounce refers to the vertical (up and down) movement of the suspension system. The upward suspension travel that compresses the spring and shock absorber is called jounce, or compression. The downward travel of the tire and wheel that extends the spring and shock absorber is called rebound, or extension.

When a spring is deflected, it absorbs energy. Without shocks or struts, the spring will extend and release this energy at an uncontrolled rate. The spring's inertia causes it to bounce and over-extend itself. Then it re-compresses, but will again travel too far. The spring continues to bounce at its natural frequency until all the energy originally put into the spring is used up by friction.

If the struts or shock absorbers are worn and the vehicle meets a bump in the road, the vehicle will bounce at a frequency of the suspension until the energy of the bump is used up. This may allow the tires to lose contact with the road.

Struts and shock absorbers that are in good condition will allow the suspension to oscillate only through one or two diminishing cycles, limiting or damping excessive vibration.

By controlling spring and suspension movement, components such as ball joints and tie rods will operate within their design range and, while the vehicle is in motion, dynamic alignment will be maintained.

Spring Design


Before discussing spring design, it is important to understand sprung and unsprung weight. Sprung weight is the weight supported by the springs. For example, the vehicle's body, frame, motor, and transmission would be sprung weight. Unsprung weight is the weight that is not carried by the springs, such as the tires, wheels and brake assemblies.

The springs allow the frame and vehicle to ride undisturbed and the suspension and tires to follow the road surface. Reduced unsprung weight will provide less road shock. A high sprung weight along with a low unsprung weight provides improved ride and also improved tire traction.



There are four major spring designs in use today: coil, leaf, torsion bar, and air.



The most commonly used spring is the coil spring. The coil spring is a length of round spring steel rod that is wound into a coil. Unlike leaf springs, conventional coil springs do not develop inter-leaf friction. Therefore, they provide a smoother ride.

Coil spring strength, or rate, is determined by the length and diameter of the rod. Decreasing the diameter of the rod, the number of turns, and the tightness of the turns increases the strength of the spring. Increasing the rod diameter or the number of turns, or increasing the space between turns reduces spring strength.






Spring rate, sometimes referred to as deflection rate, is used to measure spring strength. It is the amount of weight that is required to compress the spring one inch. For example: if it takes 100 pounds to compress a spring one inch, it would take 200 pounds to compress the spring two inches.






Some coil springs are made with a variable rate. This variable rate is accomplished by either constructing the spring from material having different thicknesses, or by winding the spring so the coils will progressively bottom out. Variable rate springs provide a lower spring rate under unloaded conditions offering a smoother ride, and a higher spring rate under loaded conditions, resulting in more support and control. Coil springs require no adjustment and for the most part are trouble-free. The most common failure is spring sag. Springs that have sagged below vehicle design height will change the alignment geometry. This can create tire wear, handling problems, and wear on other suspension components. During suspension service it is very important that vehicle ride height be measured. Ride height measurements not meeting manufacturer's specifications require replacement of the springs.

Leaf springs are designed two ways: multileaf and mono leaf. The multileaf spring is made of several steel plates of different lengths stacked together and held by clips. During operation, the spring compresses to absorb road shock. The spring plates bend and slide on each other allowing movement.




The mono leaf spring is an example of a tapered leaf spring. The leaf is thick in the middle and tapers outward to the two ends.

Some vehicle manufacturers will use a transverse, or side-to-side, leaf spring. Normally, a transverse spring can be a steel multileaf or a composite mono-leaf. Composite springs are also used in longitudinal, or front-to-back, leaf spring applications.







Another type of spring is the torsion bar. The torsion bar is a straight or L-shaped bar of spring steel. Most torsion bars are mounted solidly to the frame, with the other end connected to the suspension. During suspension movement, the torsion bar will twist providing spring action.






The air spring is another type of spring that is becoming more popular on passenger cars, light trucks, and heavy trucks. The air spring is a rubber cylinder filled with compressed air. A piston attached to the lower control arm moves up and down with the lower control arm. This causes the compressed air to provide spring action. If the vehicle load changes, a valve at the top of the air bag opens to add or release air from the air spring. Air is supplied by an on-board air compressor.



An often overlooked spring is the tire. Tires are air springs that support the total weight of the vehicle. The spring action of the tire is very important to the ride quality and safe handling of the vehicle. As a matter of fact, tires may be viewed as the number one ride control component. Tire size, construction, compound and inflation are very important to the ride quality of the vehicle. The spring rate of a tire is determined by the air pressure. An over-inflated tire will have a higher spring rate and will produce excessive road shock.

Over-inflated tires will transmit road shock rather than reduce it. Over- or under-inflation also affects handling and tire wear.

When adjusting tire pressure always refer to the vehicle manufacturer's specifications, not the specifications on the side of the tire. The air pressure specified by the vehicle manufacturer will provide safe operation and ride quality of the vehicle. The tire pressure stamped on the side is the maximum pressure that the tire is designed to hold at a specific load and speed.

Front Suspensions
There are two major types of conventional front suspensions. They are dependent and independent.

Dependent Front Suspensions


The dependent front suspension uses a solid axle. This design consists of one steel or aluminum beam extending the width of the vehicle. This beam is held in place by leaf springs.

Notice that this design also uses king pins and bushings to attach the wheels outboard of the axle. Because of its load carrying ability, the solid axle is only used on heavy trucks, and off-road vehicles. It is not suitable for use on modern passenger cars for three important reasons:

Transfer of Road Shock. There is transfer of road shock from one wheel to the other due to the way the wheels are connected to the axle. This causes a rough ride and could result in loss of traction.

Unsprung Weight. Because the solid axle has a lot of unsprung weight, it needs more spring and shock control to keep the tires in contact with the road.

Wheel Alignment. The solid axle design makes no provisions for alignment.

lndependent Front Suspensions
The independent front suspension was developed in the 1930's to improve vehicle ride control and riding comfort. With the independent design, each wheel is mounted on its own axle. This allows the wheels to respond individually to road conditions. Also, with independent front suspension the sprung weight is reduced, creating a smoother ride.

Twin I-Beam
The twin I-beam is one type of independent front suspension. Although it is similar to the solid axle in many ways, it was designed to improve ride and handling. Because of its load carrying ability, it is used on pickups, vans and four-wheel drive vehicles.



The twin I-beam consists of two short I-beams supported by coil springs, and the steering knuckles which are connected by king pins or ball joints. The inner end of the axle connects to the vehicle frame through a rubber bushing. There is a radius arm connected to the frame through rubber bushings. This arm controls wheelbase and caster.

While the twin I-beam design was an improvement over the solid axle, it still has some flaws. For example, with the twin I-beam the camber and track change as the wheels move up and down creating tire wear.

Type 1 Coil Spring
Now, let's look at the coil spring suspension, another example of an independent front suspension. Notice that it is made up of the following components:

two upper control arms
two lower control arms
two steering knuckles
two spindles
two upper ball joints
two lower ball joints
bushings
coil springs
shock absorbers

Notice that the control arms are of unequal length, with the upper arm shorter than the lower arm. This design is known as the short-arm/long-arm, or the parallel arm design.

Using control arms of unequal length causes a slight camber change as the vehicle travels through jounce and rebound. While this may sound bad, it actually is not. If both arms were the same length, a track change would occur causing the tire to travel sideways. The tires would then scrub the pavement, causing tire wear and handling problems.



Notice that the shock and spring are positioned between the frame and the lower control arm. You can see that the bottom of the spring rests on the lower control arm, while the top of the spring is connected to the vehicle's frame.

The outer end of the control arm is connected to the steering knuckle with ball joints. Ball joints are simple connectors which consist of a ball and socket. The ball and socket assembly forms the steering axis for the suspension system.

One ball joint is called the load carrier, meaning it carries the load of the vehicle or the force of the spring.

The other ball joint is called the follower. The follower does not carry any weight; it just provides a pivot point and stabilizes the steering system.

Typically, the location of the lower spring seat determines which ball joint is the load carrier and which is the follower.

If the lower ball joint is the load carrier. the upper ball joint is then the follower. The control arms act as locators because they hold the position of the suspension in relation to the vehicle. They're attached to the vehicle frame with rubber torsilastic bushings. Rubber bushings are preferred because they do not require lubrication, and will reduce minor road noise and vibrations. Torsilastic refers to the elastic nature of rubber to allow movement of the bushing in a twisting plane. Movement is allowed by twisting of the rubber.

The other sleeve of the bushing is press fit into the control arm, while the inner sleeve is locked to the control arm pivot shaft. The rubber must twist to allow movement of the control arm. This twisting action of the rubber will provide resistance to movement. Some sources state that "10% of the resistance to body roll comes from the rubber bushings."

Control Arm Design


It is important to know that control arm design is matched with spring size. This produces an exact control arm position, allowing for travel over bumps. For this reason, the lower control arm must be horizontal or slightly lower at the ball joint end.

If you find that the ball joint end is higher than the inner control bushing, the springs may be weak and sagging. Weak or sagging springs may cause a track change, and can create tire wear and handling problems. If you find this type of problem during an inspection, measure the vehicle's ride height to confirm the condition of the springs.

Type 2 Coil Spring
Type 2 coil spring suspension, the coil spring is mounted on the upper control arm, and the top of the spring is attached to the frame.



In this type of design, the upper ball joint receives the weight of the vehicle and the force of the coil spring. This makes it the load carrier.

But the upper ball joint isn't the only component supporting the vehicle weight. In the type 2 coil spring suspension, the coil spring also supports the weight of the vehicle. And the movement of the coil spring is controlled by the shock absorber.

Notice that in both Type 1 and Type 2 designs, the weight of the vehicle is transmitted through the spring to the control arm at its bottom, and then through the control to the ball joint.

You should know that the load carrying ball joints carry approximately one half of the total vehicle weight. This makes them subject to severe wear.

Stabiliizers
Another important component of the suspension system is the stabilizer. This device is used along with the shock absorbers to provide additional stability.



One example of a stabilizer is the sway bar, also known as the anti-sway bar.

The sway bar is simply a metal rod connected to both of the lower control arms. When the suspension at one wheel moves up and down, the sway bar transfers the movement to the other wheel. For example, if the right wheel drops into a dip, the sway bar transfers the movement to the opposite wheel. In this way, the sway bar creates a more level ride and reduces vehicle sway or lean during cornering.

Depending on the sway bar thickness and design, it can provide as much as 15% resistance to vehicle roll or sway during cornering.

Torsion Bar


The torsion bar suspension is one more example of an independent front suspension. With the torsion bar suspension, there are no coil or leaf springs. Instead, a torsion bar supports the vehicle weight and absorbs the road shock.

Actually the torsion bar performs the same function as a coil spring: it supports the vehicle's weight. The difference is that a coil spring compresses to allow the tire and wheel to follow the road and absorb shock, while a torsion bar uses a twisting action . Other than this difference, however, the two types of suspension construction are much the same.

The torsion bar connects to the upper or lower control arm at one end, and at the other end connects to the frame. It can be mounted longitudinally, front to rear, or transversely, side to side. Unlike coil springs and leaf springs, torsion bars can be used to adjust suspension ride height.





Keep in mind, however, that torsion bars are not normally interchangeable from side to side. This is because the direction of the twisting or torsion is not the same on the left and right sides.

Because the torsion bar is connected to the lower control arm, the lower ball joint is the load carrier. This makes the upper ball joint the follower.

Notice that in this type of suspension the shock absorber is connected between the lower control arm and the vehicle frame. This allows it to control the twisting motion of the torsion bar.




Double Wishbone
The double wishbone is another type of strut suspension that is becoming more common. It combines the space saving benefits of a strut suspension system with the ability of the parallel arm suspension to ride low to the ground. This allows for a more aerodynamic hoodline.

With this design, the lower portion of the strut forms a wishbone shape where it attaches to the lower control arm. Unlike other struts, the double wishbone does not rotate when the wheels turn. Instead, the entire spindle assembly rotates on the upper and lower ball joints much like a parallel arm suspension. Since the strut does not rotate, the upper mount does not need a bearing. Instead, a hard rubber bushing replaces the bearing and helps isolate road shock.

Rear Suspensions
Just as we discussed with front suspensions, there are two types or rear suspensions: dependent and independent.

Dependent Rear Suspensions
There are two major types of dependent rear suspension: the solid axle used on rear-wheel drive vehicles, and the beam axle used on front-wheel drive vehicles.



Solid Axle, Leaf Spring
The solid axle design uses either leaf spring suspension or coil spring suspension. At one time, the solid axle leaf spring suspension was the most common design.

Its design is very similar to the front solid axle design discussed earlier. However, in this design the I-Beam is replaced with a drive axle housing, which is suspended and attached to leaf springs. The axle housing is held in place on the leaf springs by large U-bolts.

Rubber bushings are used at the front and rear of the leaf spring to reduce road shock and vibrations. The spring itself is attached to the vehicle frame through shackles at the rear, and bolts at the front.

The front part of the leaf spring acts as a control arm, holding the axle in line to control wheelbase and maintain proper tracking. The front part of the spring is shorter than the rear part. This reduces axle wind rotation (sometimes referred to as wind-up) and increases control.

Solid Axle, Coil Spring
As it turned out, the leaf spring suspension was great for load carrying vehicles, but it wasn't very well suited to passenger cars. Because of its extensive unsprung weight and stiff springs, it produced a somewhat harsh ride.



The rear coil spring suspension is a variation of the rear leaf spring suspension often found in rear-wheel drive vehicles; the leaf springs have simply been replaced with coil springs.

Because coil springs are lighter, they have less unsprung weight, creating a smoother ride. However, coil springs can't be used to hold the axle in line and so we have to rely on other methods.

The typical rear coil spring suspension uses two lower control arms to control wheelbase, and one or more upper control arms to control side motion and axle rotation.

If only one upper control arm is used, a track bar is also needed. This bar connects to the axle at one end and runs across the vehicle to connect to the frame at the other end. Rubber bushings are used at each end to reduce vibration and allow for compliance as the suspension travels through jounce and rebound.

If two upper control arms are used, there is no need for a track bar. However, these upper control arms must be mounted at an angle. The control arms are connected to the axle and the vehicle frame through rubber bushings, similar to the ones used on the front suspension.

Beam Axle, Front-Wheel Drive


The beam axle is an example of a dependent rear suspension which is used on front-wheel drive vehicles. It is lighter than rear suspensions on rear-wheel drive vehicles because it is not a drive axle.

The stamped beam axle uses coil springs and trailing arms, with a track bar to control side-to-side movement. However, just as with the front wheels in a solid axle suspension, the rear wheels are mounted on the same axle. As we said earlier, this means that the up and down movement of one wheel can affect the other wheel. Although these movements are slight, they can cause problems in handling and vehicle control.

Twist Axle, Front-Wheel Drive


A modified version of the beam axle is a somewhat independent rear suspension called a twist axle. In it the wheels are supported by individual trailing arms that are connected to one another by a V-, U-, or I-shaped axle beam.

A flexing action takes place, due to the location of the axle beam in relation to the center line of the rear wheels and the pivot points of the trailing arms. For example, when one wheel contacts a bump in the road, the axle twists, allowing the wheels to respond somewhat independently. Another advantage of this design is that the axle shape resists bending.


Independent Rear Suspensions
There are two types of independent rear suspensions typically found in passenger cars and light trucks.



Trailing Arm
The trailing arm suspension is also known as the control arm suspension. It is becoming more common in rear-wheel drive applications in both passenger cars and light trucks. The advantage of this design is that it allows both rear wheels to move independently.

Short-Arm/Long-Arm


A newer design of rear suspension is the short-arm/long-arm suspension. This suspension is mounted on a sub frame. The two lower control arms control the wheelbase, while the two upper control arms control lateral or side-to-side movement. The steering knuckle, which houses the half-shaft, is made of cast aluminum. Variable rate coil springs are standard equipment on this suspension design.

Steering Systems


The typical steering system used on passenger cars and light trucks is called a parallelogram system because all the pivot points are paralleled. This allows each wheel to be flexible and to travel independently. The conventional parallelogram system consists of the following:

pitman arm
idler arm
tie-rod ends
center link
adjusting sleeves


Another steering system design typically used in many General Motors vehicles is also a parallelogram system. This system uses two idler arms and a drag link.



The rack and pinion steering system is usually found in passenger cars. A pinion gear translates the rotary motion of the steering wheel into the linear motion of the rack. The rack moves the tie rods back and forth to steer the vehicle. Rack placement varies from one vehicle manufacturer to another and from model to model.

"Smart" Suspensions


Today, more and more passenger cars are utilizing an active suspension system, or a "smart" suspension. A smart suspension is similar to a traditional, or passive, suspension system since many of the same components are found in each. Shock absorbers or struts, bushings and suspension components all work together to provide good handling and a comfortable ride in both systems.

However, in a smart suspension system coil springs are replaced by air bags which support the weight of the vehicle. These air bags, and usually the shocks or struts, are electronically controlled to respond to changing load and driving conditions. Most often the driver can also select a firmer or softer ride control setting to adapt to driving conditions.

In many systems, the suspension is air operated and controlled by a computer. This computer provides automatic front and rear load leveling by means of air springs. An air compressor supplies the air to the system and air flow is controlled by the interaction of the compressor, solenoids, height sensors, and the control module or computer. In addition to air springs, many systems also use dual-stage struts capable of changing their internal valving by means of a stepper motor.

Specific maintenance and servicing procedures are recommended by the manufacturer for each individual model. Typically, diagnosis of these systems involves interpreting trouble codes from the vehicle's computer and electronically measuring the many motors and sensors in the system. Refer to the manufacturer's service manual for specific procedures.

What Shocks Do


Let's start our discussion of shock absorbers with one very important point: Despite what many people think, conventional shock absorbers do not support vehicle weight. Instead, the primary purpose of the shock absorber is to control spring and suspension movement.

Shock absorbers are basically oil pumps. As shown in Fig. 1, a piston is attached to the end of a piston rod and works against hydraulic fluid in the pressure tube. As the suspension travels through jounce and rebound, the hydraulic fluid is forced through tiny holes -- orifices -- inside the piston. However, the orifices let only a small amount of fluid through the piston. This slows down the piston, which in turn slows down spring and suspension movement.

The amount of resistance a shock absorber develops depends on the speed of the suspension and the number and size of the orifices in the piston. Shock absorbers are velocity sensitive hydraulic damping devices, meaning the faster the suspension moves, the more resistance the shock absorbers provide. Because of this feature, shock absorbers adjust to road conditions. As a result, shock absorbers reduce:

Bounce
Roll or sway
Brake dive
Acceleration squat
Shock absorbers work on the principal of fluid displacement on both the compression and extension cycle. A typical car or light truck will have more resistance during its extension cycle than its compression cycle. This is because the extension cycle controls the motions of the vehicie sprung weight. The compression cycle controls the motions of the lighter unsprung weight.

Compression Cycle
During the compression stroke or downward movement, some fluid flows through the piston from Chamber B to Chamber A, and some through the compression valve into the reservoir, Chamber C. To control the flow, there are three valving stages in the piston and in the compression valves.



At the piston, oil flows through the oil ports, and at slow piston speeds, the first stage opens. This allows fluid to flow from Chamber B to Chamber A.

At faster piston speeds, the increase in fluid pressure below the piston in Chamber B causes the second stage piston valve to open. At high speed, the limits of the second stage phase into the third stage orifice restrictions.

At the bottom of Chamber B, oil that is displaced by the piston rod is passed through the three stage compression valve into Chamber C.

At slow speeds, the oil flows through an orifice in the compression valve. As the piston speed increases, the fluid pressure increases, causing the disc to open up away from the valve seat. Again, at high speeds the orifice restriction becomes effective.

Compression control, then, is the force that results from the higher pressure present in Chamber B which acts on the bottom of the piston and the piston rod area.

Extension Cycle
As the piston and rod move upward toward the top of the pressure tube, the volume of Chamber A is reduced, and thus is at a higher pressure than Chamber B.

Because of this higher pressure, fluid flows down through the piston's three stage extension valve into Chamber B.

However, the piston rod volume has been withdrawn from Chamber B, greatly increasing its volume. Thus, the volume of fluid from Chamber A is insufficient to fill Chamber B. The pressure in Chamber C is now greater than that in Chamber B, forcing the compression intake valve to unseat. Fluid then flows from Chamber C into Chamber B, keeping the pressure tube full.

Extension control, then, is the force present as a result of the higher pressure in Chamber A, acting on the top side of the piston area.

Shock Absorber Design
There are two basic shock absorber designs in use today: the two-tube design and the mono-tube design.



The conventional shock absorber is illustrated in Fig. 2. Notice that it has two tubes. The inner tube is known as the pressure or working cylinder, while the outer tube is known as the reserve tube. The outer tube is used to store excess fluid.

The upper mount of the shock absorber connects to the vehicle frame. This upper mount is called the piston rod, and at the bottom is the piston. Notice that this piston rod passes through a bushing and seal at the upper end of the pressure tube. The bushing keeps the rod in line with the pressure tube and allows the piston to move freely inside. The seal keeps the hydraulic oil inside and contamination out. It's usually of a multi-lip design made of neoprene or silicone rubber.

The base valve located at the bottom of the pressure tube is called a compression valve. It controls fluid movement during the compression cycle. The outside of the reserve tube forms the lower mounting of the shock.

Mono-Tube Design
Now let's take a look at the mono-tube shock absorber design. These are high-pressure gas shocks with only one tube, the pressure tube.



If you look at Fig. 3, you'll see that inside the pressure tube there are two pistons; a dividing piston and a working piston. The working piston and rod are very similar to the double tube shock design. The difference is that a mono-tube shock absorber can be mounted upside down or right side up and it will work either way.*NOTE A conventional two-tube shock absorber must be mounted somewhat vertically.

Another difference you might notice is that the mono-tube shock absorber does not have a base valve. Instead, all of the control during compression and extension takes place at the piston.

Actually, the shock body of the mono-tube design is much larger than needed to allow for suspension travel. A free floating diving piston travels in the lower end of the pressure tube, separating the gas charge and the oil.

The area below the dividing piston is pressurized to about 360 psi with nitrogen gas. This gas pressure tends to keep the rod extended. The oil is located in the area above the dividing piston.



* A mono-tube shock absorber improves unsprung mass when mounted upside down.

Shock Absorber Construction


Bore Size
Bore size is the diameter of the piston and the inside of the pressure tube. Generally, the larger the unit, the higher the potential control levels because of the larger piston displacements and pressure areas. The larger the piston area, the lower the internal operating pressures and temperatures. This provides higher damping capabilities.

Valving
Ride engineers select valving values for a particular vehicle to achieve optimum ride characteristics of balance and stability under a wide variety of driving conditions. Their selection of valve springs and orifices control fluid flow within the unit, which determines the "feel" and handling of the vehicle.

Full Displaced vs. Rod Displaced Valving
Full displaced valving is a significant advance in shock absorber design and construction. It reduces internal operating pressures and aeration for greater damping capabilities. Full displaced valving also provides greater latitude in engineering how a shock will perform on a specific vehicle. A typical rod displaced shock has a total of eight valving stages:

A three-stage piston valve
A three-stage base valve
Two stages as the fluid passes through the piston
Full displaced design allows ten stages by adding a blow-off valve and a dual rate piston replenishing spring.

In a rod displaced shock absorber, control is generated with the fluid displaced by the rod which goes through the base valve during compression. Fluid moving upward past the piston during the compression cycle does no significant work.

When a shock absorber with full displaced valving goes into a compression cycle, the fluid forced up through the piston is performing significant work -- it's a much more efficient shock absorber.



Full Displaced Base Valving
A. At slow piston rod speeds, fluid passes through a predetermined orifice area in the valve seat.

B. At medium rod speeds, fluid is controlled by discs which act as flat blow-off springs.

C. At high speeds, fluid is controlled by orifice slot areas in the valve plate.












Piston Valve During Compression
A. At slow piston rod speeds, an orifice controls fluid flow



B. At progressively faster rod speeds, the exclusive patented Monroe dual rate disc system provides two valving stages.

C. At very high piston rod speeds, orifice restriction controls fluid flow.






Piston Valve During Extension Cycle
A. At slow piston rod speeds, fluid is regulated by an orifice in the piston valve seat.

B. At medium rod speeds, fluid is controlled by by the spring and thickness of steel discs.

C. At high speeds, inner passage restriction provides control.

What Struts Do


Purpose of Struts
In the middle 1970's, domestic auto makers began the transition from producing large rear-wheel drive vehicles to producing lighter, more fuel efficient front-wheel drive vehicles. Along with this transition came many changes to the typical suspension system. For decades, the majority of passenger cars came equipped with short-arm/long-arm suspension systems, which are frequently called SLA's.

But with the advent of smaller, front-wheel drive vehicles, under-hood space became a premium and most front-wheel drive vehicles simply don't have enough room for a short-arm/long-arm suspension system. As a result, the MacPherson strut suspension is now the standard suspension for all front-wheel vehicles and most rear-wheel drive vehicles.

When comparing the typical SLA suspension with the strut suspension we see that the strut suspension is taller than the SLA but does not require an upper control arm, pivot shaft or bushings. This reduction in parts helps allow the strut suspension to provide a light weight, space efficient suspension system that is ideal for a variety of applications.



Strut Operation
Struts perform two main jobs. First, struts perform a shock damping function like shock absorbers. Internally, a strut is similar to a shock absorber. A piston is attached to the end of the piston rod and works against hydraulic fluid to control spring and suspension movement. Just like shock absorbers, the valving generates resistance to pumping forces created by the up and down motions of the suspension.

Also like shock absorbers, a strut is velocity sensitive, meaning that it is valved so that the amount of resistance can increase or decrease, depending on how fast the suspension moves.

Struts also perform a second job. Unlike shock absorbers, struts provide structural support for the vehicle's suspension. As a result, struts affect riding comfort and handling, as well as vehicle control, braking, steering, wheel alignment and wear on other suspenslon components, including the tires.

Strut Design


Typically, struts consist of a coil spring to support the vehicle's weight, a strut housing to provide structural support for the assembly, and a damping unit within the strut housing to control spring and suspension movement.

The bottom of the strut usually attaches to the steering knuckle, and the top of the strut is connected to the vehicle body through an upper strut mount.

With most strut suspensions, the upper strut mount replaces the upper control arm, upper ball joint, control arm pivot shaft, and control arm bushing.



The typical strut mount serves several purposes, including the following:

The flexibility of the mount allows the strut angle to change to follow the travel of the lower ball joint.
The rubber portion of the mount is designed to reduce vibration and transmitted road noise.
A bearing built into some mounts serves as the upper pivot point and forms the steering axis. When the front wheels are turned, the entire strut will pivot from the lower ball joint to the upper strut mount.
The upper strut mount carries the load and transfers that load to the spring and strut housing.
The strut body holds the damping unit and fluid. It is made of heavy gauge steel so that it is rigid enough to provide structural support and withstand road shock.

The piston rod of the strut is much larger in diameter than the piston rod of a typical shock absorber. This is to withstand the side load on the strut shaft. A strut shaft will measure up to 7/8" in diameter, while the piston rod of a typical shock measures up to 1/2" diameter.

A coil spring is located between the upper and lower spring seats. It is held there by tension. The lower spring seat is welded to the strut body, while the upper spring seat is kept in place by the upper strut mount.



During strut replacement, some struts require special service procedures. Most vehicle manufacturers use spring seats which are positioned off center and at an angle. Always mark the position of the upper spring seat and coil spring in relation to the lower spring seat. If the upper spring seat is installed incorrectly, the spring will bow, creating noise, possible vehicle pull, and premature wear of the strut and upper strut mount.

Struts also have a jounce (or compression) bumper. The purpose of this component is to limit suspension travel by not allowing suspension components to hit together. In some newer model vehicles the jounce/compression bumper is a solid piece between the upper strut mount and the top of the strut. In this case it is working as an auxiliary spring.

If inspection reveals the bumper is cracked, torn or missing, replacement is required. It should be noted that the Monroe® replacement unit has a rubber boot included with the jounce bumper to protect the strut piston rod.

Wheel Alignment


An important part of vehicle ride control is directional control. Will the vehicle travel straight down a highway? Will it steer easily? Will the tires be subject to minimum wear? Will the steering wheel return to the straight ahead position after turning a corner? For the answer to be YES to all these questions, the vehicle must be properly aligned.

Wheel alignment is the adjustment of angles made by the front wheels in relation to:

The vehicle's suspension, or Caster
The road, or Camber
Each other, or Toe
Rear wheels



The alignment of one of these angles affects the other two. All three angles are adjustable on most suspension systems.

On strut systems, there may or may not be provisions for the caster and camber adjustments. Toe is adjustable on all systems.






If caster or camber is not within specifications on a strut system where those angles are not adjustable, look for the cause in the suspension system. Do not attempt to make an adjustment by bending parts. Instead, find those parts which may already be bent, broken or worn out and replace them.

A weak strut spring may cause a vehicle to sag, which affects the caster and camber angles. ln such a case, the spring may need to be replaced.

When checking or adjusting alignment, tire pressure should be adjusted up to vehicle manufacturer specifications. Low tire pressure will affect alignment.

Caster


Caster is the forward or backward tilt of tlle steering axis. The steering axis is a line drawn through the upper and lower ball joints on a conventional suspension. On strut suspensions a line is drawn through the lower ball joint and the upper strut mount.

The caster angle is measured between the center line of the wheel spindle and a vertical line through the center of the wheel. The caster angle is positive when the center line of the spindle intersects the road in front of the tire's point of contact with the road. Caster is negative when the spindle support center line meets the road behind the tire's point of contact. Zero caster occurs when the spindle line is vertical, meeting the road at the tire's point of contact.





Most cars are designed with positive caster. Positive caster provides good directional stability by tending to return the front wheel to the straight-ahead position. It also helps the front wheels maintain the straight-ahead position -- Too much positive caster causes hard steering, excessive road shock and shimmy.

Camber
Camber is the inward or outward tilt of the tire as seen from the front. Camber is positive when the top of the wheel tilts outward, and negative when the top of the wheel tilts inward. Camber is zero when the wheel is perfectly vertical.

The camber angle is measured between the center line of the wheel (as seen from the front).

The purpose of camber is to uniformly distribute vehicle load across the tire face to minimize tire wear. Excessive positive or negative camber, however, will increase tire wear dramatically on one side of the tread -- the side toward which the top of the wheel is leaning.

Incorrect camber angles can also cause steering problems. A vehicle will steer or pull to the wheel that has the most positive camber.

Toe


Toe is the difference in the distance between the front of the front wheels and the distance between the rear of the front wheels. If the front of the wheels are closer together than the rear of the wheels, the difference in the distance is called "toe-in." If the front of the wheel are farther apart that the rear, the distance is called "toe-out."

Toe is the most critical tire wearing angle. The purpose of toe is to ensure parallel rolling of the front and rear wheels, in reference to the geometric center line; but if either wheel has too much toe-in or toe-out, the tires will slideslip. This results in a feather-edged scuff across the face of the tire.

Balance


Static Imbalance
Generally, a tire out of static balance will show wear toward the center of the road. The imbalanced weight causes the wheel to lift vertically off the surface of the road. When it lands back down on the road, the tire scuffs the road surface. This action is called wheel hop or wheel tramp.










Dynamic Balance
Dynamic imbalance causes the wheel to wobble from side to side (wheel shimmy). The tire scuffs the road surface from side to side as it rolls. Wear caused by dynamic imbalance usually shows near the edges of the tread.

Tires


Tires are the most visible component of a vehicle's suspension system, and their wear patterns can be valuable clues to the condition of other suspension system components. Tire wear is a particularly good indicator of alignment problems.

For example, tire wear can tell you when a wheel has too much toe-in or toe-out. When either one of these conditions exist, the tire meets the road at an angle. This results in the tire dragging sideways as it rolls, and the tread wearing unevenly, with a distinctive feather-edge pattern. With too much toe-in, the outside edge of each tread tends to wear off while the inner edge tends to become sharp and ragged. With too much toe-out, the reverse is true. Toe patterns can easily be felt by passing your hand across the tread.





Excessive camber angles cause tread wear on one side of the tire only. With too much positive camber, the tire will wear on the outside edge. With too much negative camber, the wear is on the inside. Again, the pattern is a distinctive one and tells you at once that an alignment is needed.

Loose or worn suspension parts can cause tire and alignment problems. Worn control arm bushings, for example, allow the tire to wobble and slip, and this causes small scuff marks in the tread. Very loose connections caused by worn bushings or, more commonly, badly worn ball joints, can result in areas of such heavy wear that they actually become depressions.









Cupping is a condition caused by the tire bouncing as it rolls. Small areas of heavy wear are created. Worn shocks are often the cause of cupping, but loose suspension parts or tire imbalance are also possible causes.



Types of Tires
There are three basic types of tires: radial ply, bias ply, and bias-belted.

Radial ply tires have ply cords which run across the center line of the tread and around the tire. The two sets of belts are at right angles. Some belts are made of steel wire, others are made of polyester or other substances. Today, radial tires come as original equipment on most passenger cars and light trucks.

Bias ply tires use cords that run at an angle across the center line of the tire tread. The alternate ply cords cross at opposite angles.

Bias-belted tires are the same as bias ply, with the addition of layers of cords -- or belts -- circling the tire beneath the tread.

Both of these types of tires will most likely be found only on older model vehicles. If upgrading from bias ply or bias-belted to radial tires, and performing an alignment, set the toe-in to the minimum amount specified by the manufacturer, set the caster to the maximum positive angle specified, and set camber to the minimum angle specified. Also, radial tuned shocks are recommended.

Gas Charged Shocks, Struts, & Replacement Cartridges


The development of gas charged shock absorbers was a major advance in ride control technology. This advance was to solve ride control problems which occurred due to an increasing number of vehicles using unibody construction, shorter wheel bases and the increased use of higher tire pressures.

Comfort vs Control
In the past, ride comfort or vehicle control were compromised by the design limits of conventional hydraulics. A shock absorber or strut can provide either a more comfortable ride or greater vehicle control, but not the optimum of both in the same unit.

A shock or strut damps excessive vehicle spring motion by the controlled movement of fluid under pressure. Fluid provides the resistance to movement. The amount of that resistance is controlled by valving.

Before Monroe gas charged shocks and struts, valve orifices could not be enlarged to increase riding comfort without losing damping effectiveness. So valving was compromised in one of two directions: soft or hard valving.

With soft valving, fluid flows more easily. The result is a smooth ride, but with poor handling -- and a lot of roll and sway.

When valving is hard, fluid flows less easily. Handling is improved, but the ride can become rough.

In the past, ride engineers had to choose between soft or hard valving. And, either comfort or control was compromised. In addition, fluid inside the shock absorber could mix with air and turn into foam. Engineers called this aeration. Because foam compresses, the amount of resistance provided by the fluid was hard to predict.

Before the development of Monroe® gas charged shocks and struts, other ways to solve these problems had been tried, but had not been totally successful.

The gas cell is one solution. It is a plastic envelope of hexasulphafluoride gas which is installed between the reserve tube and the pressure tube of a two-stage shock absorber. The gas cell fills the air space to reduce aeration.

High pressure gas charged shocks are mono-tube shocks, with fluid and gas in separate chambers in most designs. The gas can be charged to 360 psi.

The advanced design of Monroe two-tube gas charged shocks solves many of today's ride control problems by adding a low pressure charge of nitrogen gas in the reserve tube. With the shock fluid under pressure, aeration is greatly reduced.

The gas pressure also provides resistance to fluid entering the reserve tube. This, combined with the large piston bore design on Monroe shocks, provides the extra working capacity needed for lower spring rate suspensions.

With Monroe gas charged shocks and struts, you and your customers can enjoy a better ride -- plus improved handling.

How They Work


The pressure of the nitrogen in the reserve tube of a Monroe® gas charged shock varies from 100 to 150 psi, depending on the amount of fluid in the reserve tube. The gas serves several important functions to improve the ride control characteristics of the shock.

One function is to increase the resistance of fluid flow into the reserve tube. This improves valving performance during the compression stroke and also prevents "dumping" into the reserve tube.

Another function is to minimize aeration of the unit's hydraulic fluid. The pressure of the nitrogen gas prevents air bubbles or foam from weakening the hydraulic effectiveness of fluid flow through both the piston and base valve systems. Foam affects performance -- foam compresses, fluid does not.

A third important function of the gas is to allow Monroe engineers greater flexibility in valving design. In the past, such factors as dumping and aeration forced compromises in design.

Gas Charging Benefits


Here are some of the advantages provided by the advanced technology that Monroe® gas charged shocks represent.

IMPROVED HANDLING -- When turning a corner or a sharp curve, a vehicle's body tends to lean away from the direction of the turn and then rebounds. This motion is called roll. Excessive roll may cause a loss of control. With gas charged shocks, roll is reduced.

REDUCED EXCESSIVE VIBRATION -- As tires bounce up and down, road roughness is transmitted to the vehicle's body and cargo, causing them to vibrate. Excessive vibration may increase a truck's cost per mile by increasing downtime, reducing tire mileage, reducing vehicle life and lowering resale value. Gas charged shocks control tire motion better than non-gas units, so vibration is reduced.

WIDER RANGE OF CONTROL -- Because gas charged shocks reduce aeration and dumping, they can provide improved performance levels over a wider variety of road conditions.

REDUCED AERATION -- Reduced aeration means greater valving range for improved control and a reduction in excessive vibration.

REDUCED FADE -- Shocks can lose damping capabilities as they heat up during use. Gas charged shocks can cut this loss of performance, called fade.

What is Ride Control?
Many things affect vehicles in motion. Weight, weight distribution, speed, road conditions, and wind are some of the factors that affect how a vehicle rolls down the highway.

Under all these variables, however, the vehicle's suspension system -- including the shocks, struts and springs -- must be in good condition. Worn suspension components may reduce the stability of the vehicle and reduce passenger comfort. They may also accelerate wear on other suspension components, including the tires.



For example, "cupping" is a tire wear problem. "Cupping" (or small areas of heavy wear) is caused by the tire bouncing as it rolls. This tire wear pattern often indicates worn or damaged shocks or struts.

Tire wear may also be caused by incorrect wheel alignment resulting from loose or worn suspension components. In fact, tire wear can be a valuable diagnostic tool used to detect either defective suspension components or incorrect suspension alignment.

Likewise, vehicle sag can be another indicator of worn suspension components, in this case, the springs, as they are no longer able to support the weight of the vehicle at its specified design height. This may also affect the front end alignment.

Replacing worn or inadequate shocks and struts helps maintain good ride control:

Steering stability and control will be improved
Wear on suspension components and tires may be reduced by eliminating excessive bounce or vibration, and
Improved riding comfort


Ride Control Products
Gas Charged Shocks & Struts
Gas charged shocks and struts are available for most passenger cars and light trucks. These units are the most popular shocks and struts sold today. A gas charge helps keep fluid inside the shock or strut from foaming.

So, the unit performs better over a wider range of road conditions. Gas charged shocks and struts may also provide a mild lift to the vehicle's suspension.

Road Sensing Technology
A Breakthrough in Comfort and Control.
The Best Monroe® Ride Ever!
Monroe engineers have developed a line of "state-of-the-art" gas charged shocks and struts with superior riding comfort and added control.

Only Monroe has shocks and struts with Road Sensing technology that automatically adjusts the ride as the wheel position changes. This means that only Monroe can give your customers both a smooth, comfortable ride during normal driving and added control for more demanding driving conditions, such as rough roads or sudden maneuvering and stopping.

The key to Monroe Road Sensing technology is the exclusive PSDTM (Position Sensitive Damping) valve. PSD valving features precision tapered grooves in the pressure tube. Every application is individually tuned; tailoring the length depth, and taper of these grooves to assure optimum ride comfort and added control.



Here's How It Works
Position 1:
Normal Driving/Comfort Zone
Piston travel remains within the limits of the "mid-range" of the pressure tube
Tapered PSD grooves in the tube allow hydraulic fluid to pass freely "around" and "through" the piston during its mid-range travel
This action reduces resistance on the piston, assuring a smooth, comfortable ride
POSITION 2:
Demanding Driving/Control Zone
Piston action travels out of the "mid-range" area of the pressure tube and beyond the PSD grooves.
Entire fluid flow is directed through the piston valving for "more" control of the vehicle's suspension
This results in improved vehicle handling and better control without sacrificing ride comfort.
When you install new Monroe Road Sensing shocks, your customers will notice added comfort and a more confident feeling behind the wheel. For comfort and control, you can't recommend a better shock or strut than The Road Sensing One® by Monroe.

Ride Control Products for Special Applications
There are several types of ride control products designed to meet special driver and vehicle needs.

Stabilizing Units/Load Adjusting Shock Absorbers
These shocks are designed to improve the load-carrying ability of a vehicle's suspension,*NOTE so the vehicle rides right under loa

I don't understand...Can you repeat that??

contour_phoenix_when WTF?

opps guess I should have just listed the link so here it is
Tony D and bentleywarren

http://www.monroe.com/tutmen.htm

very interesting I thought so read learn now choose

stupid question

is there a shop out there that will let you try combinations of struts and springs before buying them or is is just you look at a chart of weights and measurements like spring rates lowering raising etc and choose what might be best for you and hope for the best and live with what you choose.

Originally posted by contour_phoenix_when:

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http://www.monroe.com/tutmen.htm

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what the hell does this have to do with my post?