fundamentals of suspension & 4-wheel alignment of...fundamentals of suspension & 4-wheel...

Fundamentals ofSuspension & 4-Wheel

Alignment

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Page - 2 Fundamentals of Suspension & 4-Wheel Alignment

Copyright 1996

Personal Notes


Table of Contents

SPRINGS ------------------------------------------------------------------------- 5TORSION BARS ------------------------------------------------------------------------- 6COIL SPRINGS ------------------------------------------------------------------------- 6LEAF SPRINGS ------------------------------------------------------------------------- 7AIR SPRINGS ------------------------------------------------------------------------- 8SHOCK ABSORBERS ------------------------------------------------------------------------- 9MACPHERSON STRUT ------------------------------------------------------------------------- 11CONTROL ARMS ------------------------------------------------------------------------- 13BALL JOINTS ------------------------------------------------------------------------- 15STRUT ROD/BUSHINGS ------------------------------------------------------------------------- 18SWAY BAR SYSTEM ------------------------------------------------------------------------- 19STEERING SYSTEM ------------------------------------------------------------------------- 20STEERING LINKAGES ------------------------------------------------------------------------- 22PITMAN ARM ------------------------------------------------------------------------- 23IDLER ARM ------------------------------------------------------------------------- 24CENTER LINK ------------------------------------------------------------------------- 24TIE ROD ENDS ------------------------------------------------------------------------- 25ALIGNMENT ANGLES ------------------------------------------------------------------------- 26RACK & PINION ------------------------------------------------------------------------- 27PRE-INSPECTION ------------------------------------------------------------------------- 33TIRE INSPECTION ------------------------------------------------------------------------- 34RIDE HEIGHT ------------------------------------------------------------------------- 36CAMBER ------------------------------------------------------------------------- 37CASTER ------------------------------------------------------------------------- 42STEERING AXIS INCLINATION ---------------------------------------------------------------- 47FWD CRADLE ALIGNMENT--------------------------------------------------------------------- 52TOE ------------------------------------------------------------------------- 54TOE OUT ON TURNS ------------------------------------------------------------------------- 57SETBACK ------------------------------------------------------------------------- 59THRUST ANGLE ------------------------------------------------------------------------- 60GLOSSARY ------------------------------------------------------------------------- 62


Welcome to the

Alignment TheoryWorkbook

This manual is designed to give you a solid foundationfrom which you can further your career in the ever-changing field of Automotive Alignment. It is not,however, designed to be a “Teach Everything ThatThere Is To Know” manual. Instead, each chapter willdeal with the basic information about either a part ofthe car or an alignment angle, what it does, and whatcan happen if it is worn, damaged, or incorrectlyadjusted.

Whenever possible, it is recommended that you haveaccess to a vehicle with a suspension or steeringlinkage system similar to the one discussed in thesection you are currently reading. This way, you cannot only read about and see pictures of different sys-tems, but you can observe, first-hand, the actual parts,where they are located, and how they move or actwhen the vehicle is bounced or in motion. You willnotice there is a space for your own personal notes oneach page. After looking at a vehicle and seeing thepart or parts being studied, you may find something inparticular strikes your eye or looks different thandescribed. Make notes of these observations in thespace. If you have a particular question about whatyou are seeing or about the text you are reading, makea note.

Personal Notes


TYPES OF SPRINGS

SPRINGS

FUNCTION

* Allows suspension movement for better tire to road contact* To maintain correct chassis ride height.* To assist in absorbing road shock.

The construction of springs is an elastic material suchas steel, rubber, or plastic. The spring uses thevehicle’s weight to push the tire into constant contactwith the road. Sir Isaac Newton once observed that,for every action there is an equal and opposite reac-tion. The opposite reaction to the weight pushing the

tire onto the road surface is to push up on the vehicle.This is how a spring maintains the correct chassis rideheight.

When the tire meets an obstruction on the road, forexample a pot hole or bump, it pushes up into thewheel well (jounce), or drops down into the road hole(rebound). The spring stores tremendous energyduring jounce. The spring releases tremendous en-ergy during rebound. This storing and releasing ofenergy causes the spring to “oscillate” or bounceseveral times until releasing all excess energy. Whilethis oscillation is occurring, the tire will change itsrelative position to the road surface, causing a scrub-bing of the tire tread, as well as handling problems forthe driver.

Air Spring Leaf SpringCoil Spring

Composite LeafTorsion Bars


All of this work causes the spring to weaken. As itweakens, it can no longer hold the vehicle weight aswell. It cannot keep the tire as firmly planted on theroad. As it weakens, it also causes undue forces onother suspension parts, causing them to wear outprematurely. Never heat springs to alter a vehicle'ssuspension height.

These springs come in several different designs:

TORSION BARSThe torsion bar is simply a round bar of steel that iscapable of being twisted and storing energy. One end

of the torsion bar is an-chored to the frame of thevehicle. The other end isanchored to one of thecontrol arms. As jounceand/or rebound occurs, thetorsion bar is twisted moreor less. The elasticity of thespring steel tries to returnthe bar to its normal posi-tion, thus dissipating theenergy stored during thetwisting of the bar.

Vehicles are designed touse either Longitudinal tor-sion bars, (parallel to thesides of the vehicle), or

transverse torsion bars, (across the car from side toside). In both designs, there is usually an adjustingbolt or nut at one end of the torsion bar. This adjust-ment restores the correct ride height when the torsionbars begin to weaken. Check and adjust torsionbars before performing an alignment.

Twisting Motion of aTypical Torsion Bar

Personal Notes


COIL SPRINGSA coil spring is nothing more than atorsion bar wrapped around a cylinderinto a coil shape. As they move up anddown during jounce and rebound, thebar of spring steel is actually twisting.As it twists, it gets shorter and thenlonger as it untwists, or unwinds.This is why you always see a brokenspring come to a point. With bothtorsion bars and coil springs, the twistis throughout the steel. Deep nicks orscores on the metal surface weakenthe spring at that point. Then, duringthe jounce cycle, a break occurs. Thebreak starts at the point where the nickor score mark is and continuing aroundthe bar until it breaks completely.

Coil spring suspensions do not have any method foradjustment to compensate for weakened springs. Re-place coil springs in pairs when worn or sagged.

Coil springs are often identified byspring rate. Spring rate is the amountof weight, in pounds, it would take tocompress a coil spring one inch.


LEAF SPRINGSLeaf springs are usually constructed of spring steel.However, some manufacturers use fiberglass-rein-forced plastic (FRP) for these springs, such as theCorvette and Chevy Astro van. These springs aremade in the form of flat slats, or leaves, that generallyhave a slight curvature to them. The amount ofcurvature is called the spring ARCH. As jounce andrebound occur, the spring leaf tends to flatten out fromits arch and then return to its original shape. Leafsprings are designed with three point attachments,(one at each end to the frame, a third to the axle). Leafsprings hold the axle in its correct alignment to theframe. A center bolt passing through the spring andresting in a locating hole in the axle spring seatassures axle to spring alignment.

AIR SPRINGSThe air spring is a rubberbag filled with air. In mostapplications, an air springwill provide a softer ridethan conventionalsprings. If a force is ap-plied that compresses theair it will shorten the airspring. As the air returnsto its original state it willlengthen the air spring,therefore acting like a con-ventional spring. Manysystems are controlledby an on-board com-puter and must be

switched off before alignment is performed.

Take precautions when jacking or hoistingvehicles equipped with air suspensionsystems. If an air spring is extendedwithout adequate air pressure, the wallsof the air spring can collapse inward over

Typical Air Spring Cutaway

Personal Notes


the piston. Without air in the spring, damageto the spring can occur when the controlarm moves upward.

Most vehicles equipped with air spring suspensionsystems have ride height sensors which can be ad-justed a small amount to correct ride height.

Consult vehicle service manuals for moredetails on these systems.

SHOCKABSORBERS

Earlier, we talked aboutthe oscillations that aspring goes throughwhile storing and releas-ing energy. This oscilla-tion, if allowed to go un-checked, would causeserious handling prob-lems for the driver, aswell as braking problems and tirewear. Therefore, each spring isequipped with a spring oscillationdampening device (shock ab-sorber).

If we simply dropped a weight at-tached to a spring, the weightwould move up and down until theenergy dissipates within the spring.What do you think would happenif we dropped the same weight,attached to the same spring, into aglass of oil? What if the weight hadbig holes in it? Smaller holes? Still

smaller holes? The holes would allow some of the oilto pass through the weight, cushioning its impact withthe oil. This is the principle of the basic shock ab-sorber. The piston end is attached to the frame of the

Shock Absorber

SHOCKABSORBERPRINCIPLE


vehicle. The cylinder end is attached to the axle orcontrol arm. When the wheels meet a bump, thecylinder is pushed upwards. The cylinder is a sealed,oil filled container whose inside diameter is the sameas the outside diameter of the piston valve. As thecylinder pushes upwards, oil is pushed through theholes in the piston valve. The size of the holes and thethickness (viscosity) of the oil determines how muchcushioning or resistance to movement the shock has.This way, the shock absorber takes much of the strainaway from the spring by dissipating some of the en-ergy through its cushioning effect. Stiffer shocks orheavy duty shocks will provide a firmer ride. The firmerride will result in less suspension movement. Heavyduty shocks could be needed for high performancevehicles or vehicles carrying heavy loads or frequenttravel over rough roads. Shock absorbers do not affectride height unless it is a spring assisted or air assistedtype.

Many shock absorbers are "Gas Filled" for improvedconsistency and longer life. Gas filled shocks arecharged with nitrogen gas which decreases aeration(foaming) of the oil inside the shock.

Because of its job duties, check the shock absorber forany broken mounts, deteriorated bushings, or leak-age around the piston seal. In addition, perform abounce test. Bounce each corner of the car severaltimes and then watch that corner after you release it.It should not bounce more than two and one-half times.Be careful not to use just the bounce test to condemnthe shock. A weakened or broken spring causes thevehicle to bounce excessively. Also inspect the tirefor a scalloped or cupping appearance. This couldindicate that the shock or spring is bad, allowing thetire to leave the road and then slam down again.

Piston Rod Seal

Reserve Fluid

Piston / Valving

Fluid Under Pressure

Base Valve

Shock AbsorberConstruction

Personal Notes


MacPherson StrutIn the late 1940’s, a clever engineer thought up a newway to get the same steering geometry as a conven-tional upper and lower control arm system, but usingfewer parts. Additionally, he found that his designcould spread suspension loads to the body over awider span. The road shock could get to the springwithout having first to go through a control arm. All ofthese characteristics made for a more comfortable rideand safer handling. This design had one shortcoming;it had to have the upper portion of the frame and fenderwell reinforced. Because of that, domestic car manu-facturers decided not to adopt his design. So, Earle S.MacPherson took his design to Ford of England,where the MacPherson strut suspension made itsdebut in 1950.

The MacPherson strut is a unitized design that incor-porates the spring, shock absorber, upper control arm,and upper bearing plate all in one unit. The upperbearing plate functions the same as the upper ball jointin the conventional SALA Suspension system. By itsdesign, any road shock is transferred directly from thetire to the spring, without having to pass through acontrol arm, thus producing a smoother ride. By plac-ing the load point of the spring up higher, and increas-ing the width between the springs, this design alsogives excellent anti-roll characteristics. By using fewerparts, the MacPherson strut also takes up less space,thus creating more room for the engine, and anyrelated accessories like air conditioning and powersteering.

The top of the strut is mounted in a rubber and metalassembly, called the upper strut mount. Althoughdesigns differ somewhat from car to car, basically themount will have a bearing assembly, guide sleeve forthe strut piston rod, and a rubber isolator pad. The strutitself is designed much like a shock absorber, with apiston rod, piston valve, and an oil chamber. If the strutis “rebuildable”, there will also be a centering collar forthe piston rod. The top of the piston rod is threaded,and passes through the upper strut mount, where it is

MacPherson StrutSuspension

Conventional SALASuspension

UpperBearing PlateUpperSpring Seat

Coil Spring

Piston Rod

Strut BodySpanner Nut

LowerSpring Seat

Strut Body

Lower StrutMount


retained by washers and a nut.

Just below the mount is the upper spring seat (some-times part of the mount). The top of the spring rests inthis seat. There is usually an indicator notch to showwhere the end of the spring should be. Welded to thestrut body is the lower spring seat, also with an indica-tor notch. The spring is held between these two seatswith tremendous pressure. Because of this, neverremove the piston rod nut until a spring compressor isinstalled and holding the springs in place.

The strut may be attached at its lower end in one of twobasic ways. It may be bolted to the steering knuckle orit may be bolted directly to the lower ball joint, if thespindle is part of the strut.

There is another strut design called Modified Strut.This design utilizes a spring on the lower control armthat contains a load carrying ball joint. This system isvery similar to the SALA suspension in the design ofthe lower control arm and the spring position. Thegreatest difference between it and the SALA is that theupper control arm is replaced by the Modified StrutAssembly. The upper bearing plate acts as the upperpivot.

Diagnosis of a MacPherson strut should entail morethan just looking to see if the “shock” part is leaking.There is a difference between leakage and seepage.Most struts will seep a little oil through its seal. It isnormal to see a light film of oil only at the top of the struttube. Recommend replacement if the oil film is thickand runs down the side of the tube. Also, if you havealignment equipment attached, raise the car aboutthree inches and lower it by the same amount whilewatching the camber. If both wheels do not changecamber by the same amount, and in the same direc-tion, you probably have a bent strut tube or piston rod.By loosening the piston rod nut (LOOSEN, DO NOTREMOVE!) and rotating the piston rod, you can watchthe tire for any camber change. If it is changing, thepiston rod is bent; if not, the strut tube is bent.

Personal Notes


Short Arm / Long Arm Suspension

CONTROL ARMSAs their name implies, control arms control or restrictsomething. What do they control? Control armscontrol the path of travel that the tire can haveduring jounce and rebound. The most commonarrangement of these control arms is to have a shorterone on top and a largerone on the bottom. Thissystem’s name is “shortarm, long arm” orSALA suspension. Be-cause of the differencein their sizes, the con-trol arms move in differ-ent arcs during jounceand rebound. Thesmaller, upper controlarm moves in a largerarc and tends to movethe top of the tire only.The larger, lower arm moves in a much smaller arc,and moves the bottom of the tire very little. This way,tire scrubbing is minimized while allowing the chassisto move up and down by a largeramount.

In order for the control arms to move,they must have pivot points. The innerpivot point is attached to the frame witha shaft and bushings. Some vehiclesare equipped with two independentshafts (bolts), instead of one single-piece shaft. Regardless of the type,they all use bushings. Most cars andlight trucks use a rubber bushingbonded to both inner and outer metalsleeve. The outer sleeve is pressedinto the control arm housing, while theinner sleeve is attached, through ser-rated edges, to the shaft. When thecontrol arm is moved up or down, theouter sleeve is rotated with the arm,while the inner sleeve stays put on the


shaft. This causes the rubber sandwiched betweenthe sleeves to be twisted like a rubber band, thus ittries to un-twist. This bushing, then, acts as a littlespring and helps to keep the control arm in its properposition. It also dampens some of the vibrationscoming from the tire and wheel assembly.

When inspecting these bushings, check them in theirnatural position, with thewheels on the ground. Lookfor obvious deterioration andbreakage. Also, make sure thebolt or shaft is going directlythrough the center of the bush-ing. If the shaft and bolt areoffset from the center, the

bushing has taken a “set” and will not functionproperly. It may also cause variations in alignmentangles when the forces of driving are applied. Whenreplacing these bushings, use a suitable driver orbushing installation tool to install them in the control

arm, and be sure to drive them instraight. Install the bushings atthe proper angle to the hole toeliminate damage to the controlarm. DO NOT TIGHTEN THERETAINING BOLT FULLY UN-TIL THE VEHICLE IS IN ITSNORMAL RIDE HEIGHT POSI-TION. Failure to do so will causethe bushing to have a pre-set

twist, thus defeating one of its purposes, and leadingto premature failure of the new bushings. If you areinstalling threaded metal bushings, thread eachbushing equally onto each end of the shaft. If installedincorrectly, you may have a problem getting the casterangle set. When the bushings reach the bottom of thecontrol arm hole, the pivot shaft should rotate freely inthe bushings.

After installing the control arm in the vehicle, lubricateboth metal bushings with a hand grease gun.

Metal Threaded Control Arm Bushing

Rubber Control Arm Bushing

Personal Notes


BALL JOINTSThe outside pivot point for the control arm is usually aball joint. The construction of a ball joint is much likeyour shoulder joint. It allows motion in a circulardirection and in an arc, but not laterally (in-and-out). Ball joint construction includes a housing, a balland tapered seat, a bearing, and some form of pre-load device.

Ball joints come in two basic designs, compression-loaded and tension-loaded, and are used as eithera weight carrying pivot or a friction pivot. The designof the compression joint allows the weight of thevehicle and the upward pushof the tire and steering knuckleto compress the ball stud intothe housing. The tensionjoint is just the opposite, ve-hicle weight and the push ofthe tire and knuckle pull theball stud away from the hous-ing. In either case, the resultis to have the ball stud in con-stant contact with the bear-ing, which is the wearsurface. Most vehicles todayuse a compression joint forthe friction joint and a tensionjoint for the weight carryingjoint.

The location of the weightcarrying joint is closest tothe seat of the spring or torsion bar. As the vehicleweight passes through the spring, it must then gothrough this joint to get through the tire and to the roadsurface. With most SALA suspensions, the springrests on the lower arm, making the lower joint theweight carrying joint. Some older vehicles, however,

WEIGHT CARRYING BALLJOINTS

Friction Ball Joint(Non Load Carrying)

Friction Ball Joint(Non Load Carrying)


have the spring on the upper control arm, making theupper joint the weight carrying one.

Checking these joints is de-pendent upon unloading themproperly. When the lower jointis the weight carrying joint, jack-ing under the lower control armuntil the tire is clear of the groundwill unload it. If the upper joint isthe weight carrying joint, youmust jack the vehicle up by theframe.

On most cars that have an upper weight carrying joint,there is a travel limiter and/or bump stop to prevent thecontrol arm from hitting the frame during extremerebound. Use a suitable wedge, available from manyalignment tool manufacturers, to hold the control armaway from the frame when checking these joints.

You will find ball joint specifications in the rear of youralignment specs guide. Follow the instructions in thealignment specs guide and use a dial indicator gaugedesigned for ball joint checking to obtain these read-ings. Some ball joints may require the use of a torquewrench to check ball joint pre-load.

Special tool usedto unload upper

ball joint

Jack placed under the FRAME

Jack placed undercontrol arm

JACKPLACEMENT

FORCHECKING

LOADCARRYING

BALLJOINTS

Personal Notes


When checking a friction ball joint, notice in the specsguide that any appreciable movement is beyond theallowable tolerance. Replace the joint if any appre-ciable movement is detected in friction ball joints.

Many ball joints are pressed into the control armhousing. When you buy a replacement ball joint, it isgenerally about fifty-thousandths (.050)oversized. This is to assure proper balljoint to control arm fit. Replace completecontrol arms if the ball joint was previ-ously replaced. This is because the firstreplacement joint stretched the hole inthe control arm by .050. The secondreplacement joint will not fit properly.

Many vehicles are equipped with “Wear-indicator” load carrying ball joints. Tocheck these ball joints, the vehicle mustbe in the “DRY-PARK” position, weighton the wheels. The illustration to the leftshows a typical wear-indicator ball joint.The location of the indicator is on thebottom plate near the grease fitting. Re-place the ball joint if the indicator isFLUSH with the bottom of the balljoint. The ball joint is GOOD if the indica-tor is protruding.

PROTRUDINGINDICATES BALLJOINT IS GOOD

WEAR INDICATOR


STRUT ROD ANDBUSHINGS

Many vehicles have a lower control arm that looksmore like a letter “I” than the traditional letter “A”. The“A” shaped arm uses both legs of the “A” to secure itfrom any back-and-forth movement. The “I” shapedarm is easily moved back and forth. To prevent this,manufacturer’s design includes a rod attached to thecontrol arm at one end and to the frame at the otherend. Bushings attach the frame end. The name of thisrod is strut rod, or brake reaction rod. When applyingthe brakes the ball joint end of the control arm stops(along with the tire) but the frame end wants to

continue moving. If allowed tohappen, even slightly, there wouldbe an immediate change in caster,to the negative, which can causehandling problems. If one of the

brake assemblies on the front is more efficient than theother, the car would tend to turn to the side that had themore efficient brake.

Because of this potential for movement, many engi-neers design the strut rod withthreads on the frame end. Thisway, it is convenient to adjust thecaster angle. However, for casterto be accurate at highway speedsand during braking, the mountingbushings must be in good shape.Check them in the “Dry-Park” posi-tion for any obvious deterioration,cracking, or breaking. Replace thebushing if the strut rod position isnot in the center of the bushing.

Personal Notes


STABILIZER BARSWAY BAR

When a vehicle goes into a turn, the weight of thevehicle becomes unevenly distributed. This shiftcauses one side of the car to go downward and theother side to go upward. This weight shift also causeschanges in the camber and toe settings, and canresult in the driver having to fight the vehicle throughthe turn.

To minimize the weight shift and result-ing height changes during a turn, aspring steel bar is attached across thecar to both lower control arms and tothe frame. The swaybar does noteffect ride height when the vehicle isin the straight ahead and level posi-tion. Swaybar attachment points arethrough rubber bushings. The framebushings wrap around the bar, andshould be checked for looseness, de-terioration, and breakage. The controlarm ends of the bar are attached, usu-ally, through link kits. These link kits contain a longbolt, four bushings, washers, a sleeve, and a nut.Check the link kit for bushings that are missing ordeteriorated, sleeves that have worn through thewashers, or missing washers.

Some manufacturers also use the sway bar as astrut rod also. For example, the Ford Escort swaybar is attached directly to the lower control armwithout using a link kit. This helps to prevent anyback-and-forth movement of the arm. Constant casterchange is the result of worn or loose bushings on thisstrut rod system.

Perform all parts’ checks to this system inthe “Dry-Park” position.

Typical FrameBushing


STEERING SYSTEM

STEERING GEAR

To make the wheels turn, the rotary (around-and-around) motion of the steering wheel is converted intolateral (side-to-side) motion of the steering linkage. Aset of gears, called a steering gearbox, is used toaccomplish this motion conversion. Until recently, thisgear box was usually the “RECIRCULATING BALL”type. Let’s take a look at it—

The basic operation is easy to understand if yousimply think of a nut and bolt. Rotate the bolt (thesteering wheel and shaft) to the right and the nut isthreaded up the bolt. Rotating to the left will make thenut thread down the bolt. If we were to put some gearteeth on the nut and make it mesh with a second gear,we could make the second gear turn by rotating thebolt. In a real gearbox, the bolt is the steering shaft,and is commonly called a worm shaft. It has a verywide-spaced thread on it. The shaft is “threaded” intoa nut called a ball nut. Inside the ball nut, instead ofthreads there are a number of balls that are positionedto roll on the shaft threads. Balls are used becausethey produce less friction between the moving parts.The balls follow an endless path by means of a ballguide tube which returns the balls to their starting point

STEERING GEAR PRINCIPLE

Personal Notes


when they reach the end of the threads on the shaft. Asthe steering shaft is rotated by the steering wheel, theball nut is threaded up or down the shaft. On the sideof the ball nut is a gear. This gear is meshed with asecond gear, called the sector gear. The sector gearis held in place by the housing, and as the ball nutmoves, the meshing of the gears causes the sectorgear to rotate. Attached to the bottom of the sector gearis a splined shaft, called the sector shaft. Rotating thesteering wheel causes the worm shaft to turn in unisonand this causes the ball nut to move. The ball nutmoves the sector gear, which rotates the sector shaft.

The steering linkage, which will be described later, isthen attached to the sector shaft.

If the vehicle is equipped with power steering, theworm shaft is attached to a spool valve. A spool valveis simply a control gate which directs power steeringfluid to the ball nut (power piston) that forces it in onedirection or the other.


STEERING LINKAGESMost steering linkages are of one of four types:

CROSS STEERING...used primarily on four-wheel drive axles

CROSS STEERING LINKAGE SYSTEM

PARALLELLOGRAM...used on many cars and light trucks

HALTENBERGER STEERING LINKAGE SYSTEM

PARALLELOGRAM STEERING LINKAGE SYSTEM

Rack and PinionSteering System

RACK & PINION used on most modern cars & many light trucks.

HALTENBERGER...used primarily on Ford Twin-I beam suspensions

Personal Notes


One of the most common steering systems is theParallelogram, it contains four main parts; an idlerarm, a pitman arm, tie rod ends, and adjusting sleeves.Its name is derived from the fact that the tie rod endsare roughly parallel to, and about the same length as,the lower control arm. This is to prevent the tire fromgoing through drastic toe changes during jounce andrebound. The tie rod end and the ball joint both movein similar arcs, so that the tire position can be un-changed during movement.

PITMAN ARMThe PITMAN ARM is the first component to be movedby the steering gearbox. The pitman arm stud is themost heavily stressed joint in the steering system,since it must move all of the rest of the steering linkage.You can easily check it by hav-ing the wheels of the vehicleresting on your rack (lockedturntables, if used), and thenrocking the steering wheel backand forth. The pitman arm stud,the pitman arm, and the centerlink should all move as oneunit. Replace the pitman arm ifyou see that the pitman arm ismoving but not the stud (at thesame time and at the samerate of movement). Lookclosely, however, at the stud. Isthe stud actually a part of thepitman arm, or is it a part of thecenter link? Many parts cata-logs will list “N/A” for the pitman arm. This indicatesthat the only wearable part (the stud) is on the centerlink and not the pitman arm.


IDLER ARMThe pitman arm’s partner is the IDLER ARM. Theyboth support the center link in its correct horizontalplane. The idler arm can be one of three basicdesigns: rubber bushing, integral arm with nylonbushings, or threaded steel bushing. Regardless of itsdesign, the idler arm must not move up or downexcessively. If it does, the center link will move outof its horizontal plane and can cause what is referredto as “bump steer”. The allowable movement in anidler arm is an old argument. Some General Motorsservice manuals state that when twenty-five pounds offorce is exerted on the idler arm at the center linkconnecting point, the idler arm should not move morethan 1/8" in either direction (up or down). Later modelGM “F” body products (Camaro and Firebird) have theidler arm mounted to the frame in elongated holes.Adjust it up or down to eliminate bump-steer after thesprings have weakened more on one side than theother.

You should remember that the idler arm, if exces-sively loose or worn, will cause toe changes whilethe vehicle is in motion.

CENTER LINKThe center link is a bar between the pitman arm andthe idler arm, to which the tie rod ends are attached.Therefore, it is the means of connecting the tires to thesteering gear box. It is designed to travel in ahorizontal plane, pulling one tie rod end with it whilepushing the other to make the tires turn. At each endof the center link is either a hole or a stud, forattachment to the idler and pitman arms. Two otherholes are about one-fourth of the way in for attachingthe tie rod ends. GM “F” body cars (Camaro andFirebird) have a machined flat spot on the center link

Bushing Integral

RubberBushing

ThreadedMetal Bushing

Personal Notes


at each end. These flat spots are measuring points toestablish whether the center link is horizontal or not. Ifnot, then move the idler arm slightly up or down so thatboth flat spots are within 1/16" of each other.

TIE ROD ENDSThe tie rod ends are much like little ball joints. Theyallow motion in a circular direction, but not laterally.There are two on each side of the car, the inner andouter tie rod ends. Tie rods are positioned to closelymatch the travel of the lower control arms. This mini-mizes the inward and outward movement of the wheelswhen the suspension travels through jounce and re-bound. The inward and outward movement is ToeChange.

The inner tie rod end is attached to the center link andallows the wheels to move up and down in relation tothe center link. The outer attaches to the steering arm,which either attaches to the steering knuckle or is aforged part of the knuckle. This allows the tires to turnaway (left or right) from the straight ahead position.Both tie rod ends are connected to each other by anADJUSTING SLEEVE. The sleeve is a threadedtube. By turning it, the two tie rods can be moved closertogether or farther apart, thus moving the tires inwardsor outwards.

Prior to tightening the tie rod sleeve clamps, positionthe tie rods so the stud is centered in the housing of thetie rod ends.Position the clamps so the split in the clamp is NOMORE THAN 45 degrees away from the split in the tierod sleeve. This will distribute force more evenlyaround the adjusting sleeve. Do not align the splits ofboth sleeve and clamp.Like the pitman arm, the easiest and more accuratemethod of checking a tie rod socket is by moving thesteering wheel back and forth, with the wheels onthe rack, and checking the stud for any movement. Ifyou see movement, then the toe angle will changeas the vehicle moves down the road, causingexcessive tire wear.

IncorrectStud Alignment

CorrectStud Alignment

Correct Clamp Alignment

Incorrect ClampAlignment


Rack and PinionSteering System

Parallelogram SteeringSystem

RACK & PINION PRINCIPLE

Rack & Pinion SteeringEarlier, we discussed the parallelogram steering link-age. Recently, that has been replaced with rack &pinion steering, which is simply a redesigned paral-lelogram. Let’s take a closer look at it, and compare thetwo systems.

On a parallelogram system the componentthat ties the right and left sides together is thecenterlink. This piece is also in the rack &pinion system, but it has been designed withteeth on one end, and is now called a rack.The centerlink is held in its proper horizontalplane by the idler arm and pitman arm. Therack is held in its proper horizontal plane by

the rack housing.

The centerlink is used to at-tach the tires to the steeringsystem through the tie rodends. The rack does thesame thing, using an outertie rod end that is very simi-

lar to the ones used with parallelogram linkage. Theinner tie rod end has been redesigned so that the tierod stud sticks out very far, and the socket itself screwsonto the end of the rack.

If you look carefully at an installed rack & pinion, youwill notice that the inner socket assembly and outer tierod lie in a plane that is roughly parallel to the lower

control arms, just like in a parallelo-gram linkage system. Because of this,it is important that a rack & pinion beinstalled correctly. If the mounting bush-ings and/or straps are deformed or bent,the rack housing will not be held in theproper position, creating a “bump steer”condition, where the car wanders andweaves after hitting an obstruction inthe road.

Personal Notes


The last piece of the rack & pinion is the pinion gearitself. This takes the place of the conventional steeringgearbox. The steering column is attached to the inputshaft, through a flexible coupler. If the vehicle hasmanual steering, the input shaft simply ends in a gearthat meshes with the teeth on the rack. A lash adjusteris located directly below the rack where the meshingoccurs. Usually of plastic and spring loaded, thisadjuster is used to compensate for any wear in the rackand/or pinion teeth. When an adjustment is needed,consult the service manual for the vehicle to find thefinal torque specification for steering input. The ad-juster is tightened (or loosened) until a predeterminedamount of steering wheel torque is required to makethe rack move.

If the vehicle is equipped with power-assist steering,the pinion gear looks slightly different. Instead of asimple one-piece shaft ending in a gear, it is now athree-piece assembly. The steering column is attached,again through a flexible coupler, to the input shaft. Thisshaft has a machined center section with cutouts in it.These cutouts are called “windows” and the corre-sponding machined surface is called a “door”. Thesplined shaft is hollow, with a hole at the top for aretaining pin.

The third section of the assembly is the pinion gearitself. Notice that it has a long, thin bar attached to it.This is a torsion bar. The torsion bar runs up through


the hollow input shaft and is pinned at the top. Thesplined bottom of the input shaft meshes with a splinedsection inside the pinion gear. There is a considerableamount of “slop” or free play in this splined section.This is designed so that the customer will have somecontrol over the vehicle when power-assist has failed.As the steering wheel is turned, the free play in thesplined coupling is taken up. After the free play iseliminated, the pinion gear meshes with the rack teeth.At this time, the torsion bar begins to twist.

Wrapped around the center section of the input shaft,and attached to the pinion gear, is the spool valve. Theinside of the spool valve is a mirror image of themachined “doors” and “windows” of the input shaft.The spool valve is precisely located so that a spoolvalve door is covering an input shaft window all aroundthe diameter of the input shaft. However, as the torsion

bar is twisted, the input shaftmoves slightly. As it moves,windows and doors becomemis-aligned, and a path forfluid flow is established.

Power steering fluid flows from the pump and entersthe rack housing where the spool valve sits. On theoutside of the spool valve are several large holes inthe center section of the spool. Look inside the spool,and you will notice that the large holes open into thewindows. There is also a large hole in the matchinginput shaft door. With no pressure applied to thesteering wheel, the spool valve is aligned with theinput shaft, allowing the fluid to simply enter andcirculate back to the pump.

On the outside of the spool are two other sections,upper and lower, with smaller holes spaced 45 de-grees apart from each other. These holes open intothe spool doors. As the torsion bar is twisted byturning the steering wheel, a part of the spool door

hole and the input shaft door hole begin to line up witheach other. The power steering fluid is forced throughthe smaller holes, and exit into a tube.Attached to the rack is a piston with a Teflon seal. Theseal presses against the rack housing to divide thehousing into two sections. As fluid is directed from the

SPOOL VALVE

Personal Notes


spool valve, it enters one of two tubes. These tubes arepositioned to enter the rack housing on either side ofthe piston. If the fluid under pressure enters on the leftside of the piston, it will push against the piston. Sincethe piston is attached to the rack, the rack moves to the

right, and since the tie rod ends are attached to therack, they also are pushed to the right.

If the rack & pinion is installed behind the front axle(rear steer), as the rack moves to the right, the tires willbe steered to the left. If the rack is installed in front ofthe axle (front steer), the tires would go to the right.

At each end of the rack housing are seals that keep thefluid inside the pressure chamber, as well as keepcontaminants from entering and corroding the rackand/or chamber. If these seals go bad, the pressurizedfluid can leak past them and enter the protectivebellows boot that surrounds the inner socket assem-bly. By squeezing the bellows, you can feel for anyfluid in them. If the problem remains, the bellows willeventually balloon up and rupture.

POWER STEERING

SPOOL VALVEFLUID

FLUID DISPLACEDBY THE PISTON

FLUID PRESSURE ROUTED BYSTEERING MOTION

FLUID RETURN LINE


There is a tube that runs from one bellows to the other.This is the breather tube. It is used to equalize the airpressure within the bellows during turns. Any fluid thatenters one of the bellows will be pumped to the otherone as the vehicle is turned to the right and left. Thesebellows can hold up to approximately 1 quart of fluidbefore rupturing. If you have a customer complaint ofhaving to add fluid to the reservoir, without any signsof leakage present, it would be a good idea to checkthese bellows.

Another common customer complaint has to do withhard steering. Primarily, hard steering complaints canbe divided into two areas; those that occur constantly,and those that occur only during the first hour of

driving. If thecustomer com-plains of hardsteering con-stantly, checkthe power steer-ing fluid level,power steering

pump belt and the power steering pump. If no problemis found in these components, a very likely problemarea is the pressure chamber inside the rack & pinion.After several thousand miles of driving, the hard Teflonseal that is around the power piston begins to wear abarrel shaped area, on either side of the piston, in thechamber wall. As fluid enters the chamber from the

spool valve, it is supposed topush against the power pis-ton; instead, some of the fluidby-passes around the piston.This results in pressurizedfluid on both sides of the pis-ton, creating a hard steeringeffect. This problem cannotbe cured by simply rebuild-

ing the rack & pinion, and calls for complete replace-ment of the unit.

The other hard steering problem is usually precededby the customer complaining of a hard steering effortin one direction or the other, usually the first thing afterstarting the engine. This condition may last for several

Internal Fluid Leak

Personal Notes


minutes to an hour or more and then normal steeringis restored. This complaint stems from a leakagearound the spool valve seals. In theory, the spoolvalve seals should be pressed tight against the bore ofthe housing, while the spool itself rotates. In reality,that is not always the case.

The housing, which is generally made of aluminum,expands and contracts with temperature variations.The spool valve, which is made of steel, and the seals,which are made of a Teflon and Fiberglass composi-tion, also expand and contract, but at different rates.This results in the aluminum housing getting biggerthan the diameter of the seals. As the spool valverotates, the seals also are now free to rotate, and asthey do, they slowly erode the smooth alumi-num bore into a grooved aluminum bore. Asthe vehicle sits overnight and cools down,everything shrinks back to its original size.This leaves a gap between the spool valveseals and the groove in the housing. As the caris started, the fluid, which is supposed to enterthe pressure chamber when the steering wheelis turned, simply by-passes around inside thespool valve housing, resulting in little or nopower assist to the power piston inside therack housing. However, as the fluid heats upand the ambient temperature heats up, theseals slowly swell and begin to press up againstthe bore, restoring the power assist. After-market manufacturers are installing steelsleeves in this bore to eliminate the erosionfrom the seals.

Internal Spool Valve Leakscan cause hard steering


ALIGNMENT ANGLESAutomobile manufacturers have understood for many years that their products weaken andwear after a period of time. Springs weaken and begin to collapse. Suspension parts andsteering parts wear out and become loose. Frames bend or collapse slightly. All of these thingscombine to make the car less pleasurable to drive. It is also more costly in terms of gasconsumption, accelerated parts wear and increased tire wear.

To help decrease these problems, auto manufacturers designed a method of adjustment intothe suspension and steering systems. These adjustments allow a technician to compensate forwear related changes. A set of specifications with allowable tolerances has been establishedby the auto manufacturers. Vehicles are measured and these measurements are compared tothe specifications. Those measurements that are not within the allowable tolerances must beadjusted. These settings are referred to as the alignment angles. Just as any measured setting,such as brake rotor thickness, or spark plug gap, a reliable and accurate measuring device mustbe used. These alignment angles, when measured and adjusted to the recommendedsettings, should restore the vehicle’s handling, ride, and tire life to what they were originallydesigned to be.

Tire InspectionA thorough inspection can aid in diagnosing somefour-wheel alignment problems. Tire wear patternsare like a visual graph of camber and toe condition.Feathered or sawtooth wear might indicate a severetoe problem on the front. Single shoulder wear wouldprobably lead to a camber or toe problem. Diagonalcross-tread wear on the rear tires is an indication thatthe rear camber and/or toe needs correction.

Wear patterns can also help diagnose other prob-lems. Wear on both shoulders might indicate lowinflation or loose steering parts. Center tread wearusually leads to an over inflated condition. Cuppingcould lead to a wheel balance problem and/or badshock absorbers or other suspension parts.

Check the tires for those not-so-obvious conditionsas well. Check the tire sizes. The tires should be thesame height all around the vehicle. Tires should beinflated to manufacturer's recommendations. Con-

Even Tread Wear

Properly Aligned andProperly Inflated

10"Section Width

SectionHeight

6"

Vertical Dimension is 60%of the

Horizontal Dimension

Aspect Ratio(60 Series Tire Shown)

Personal Notes


sult the tire guide or the vehicle decals for the properinflation pressure. Vehicle decals may be found underthe hood, on the door post or on the glove compart-ment door. These decals may also list the proper tiresize. Check the tires for damage. Check all tires for acommon tread design. Check for different tire brands.If different, this may cause a directional pull that align-ment will not correct. Measure the height of each tire toassure that you do not overlook a tire problem. If thedriver complained of a vibration, check the runout ofeach tire and balance the tire(s) if necessary.All tire related problems should be resolved prior toperforming the alignment.

Center Tread wear

Outside Treadwear

(both shoulders)

Feathered orSawtooth

Tread wear

Single shouldertread wear

Camber Problem

Over Inflation

Under Inflation

Toe or loosesteering parts

Some tires may have another letter between theAspect Ratio and the construction letter. This letter

is the Speed Rating, i.e.; P175/60VR14.


RIDE HEIGHTThe first measurement is the one engineers use todetermine all of the other angles. Its name is RIDEHEIGHT, TRIM HEIGHT, or CURB HEIGHT. Thissetting is used to establish the correct suspensionheight at which all other angles are measured. Anincorrect ride height usually indicates that the springshave weakened and collapsed. If the ride height isincorrect, it can cause handling and tire wear prob-lems. This is because the suspension is operatingthrough different and incorrect geometry. In your align-ment specs guide you will find a ride height measure-ment at the end of each manufacturer’s section. If theride height is not within the allowable manufacturer'stolerances, the amount of adjustment movement willbe reduced. In some cases the adjustment may not bepossible.

Ride height must be checked andcorrected prior to making anyother alignment corrections.

If the vehicle is equipped with an electronic ride controlsystem, the system must be operating correctly toachieve proper alignment settings. Some systemsmay require that the system be disabled prior to align-ment. Consult the vehicle service manual for specificdetails on Electronic Ride Control devices.

Personal Notes


CAMBERA tire may be in any of three positions: the tire may leantowards the car, it may lean away from the car, or itcan be straight up vertically. The camber measure-ment tells us which of these three positions the tire isin and by how much. If the tire leans towards the carat the top, the camber is negative, and the sign (-) is used; leaning away from the car at the top ispositive (+); straight up is zero (0). Remember, ifyou obtain an alignment reading of zero, it does notnecessarily mean “no reading”; it is an actual mea-surement and is often a specification.

The amount of positive or negative camber is meas-ured as an angle from straight up (true vertical). Likean angle, it is measured in degrees. A reading of 1degree positive would indicate that the tire is leaningaway from the car by one degree from straight up.Some specifications for camber are in degrees andfractions of a degree, such as “+3/4”. Others may bein decimal degrees (+.75). Still others may usedegrees and minutes, where there are sixty minutes ina degree. A reading of +0,45' is read as zero degrees,forty-five minutes, or three-fourths of a degree.


A proper camber setting is necessary for severalreasons:

1. It maximizes the amount of tread in constant contact with the road surface.

2. It helps to establish the proper load point on the suspension.

3. If incorrect, it can cause a pull or lead in the car.

4. It is used, with another angle, to diagnosebent suspension components.

The tires are the only part of the vehicle that touch theroad, and the weight of the vehicle reaches the roadthrough the tires. Each tire must support one-fourth ofthe vehicle weight. If you relate that fact to your ownbody, your “TIRES” are your feet, and each footsupports one-half of your “VEHICLE” weight. Walkingon the outside edges of your feet is comparable to acar with positive camber. What will happen to yourshoes after several thousand miles of walking likethis? You will wear the outside edges of your shoes.In addition, you will probably notice that your outerankle is sore and swollen. That is because yourweight passed directly through it, instead of beingsplit between the ankles. On a vehicle, the ankles arethe wheel bearings, and excessive camber willcause premature wear to the bearings, especially inthe case of positive camber and the outer wheelbearing.If you lean a tire slightly, and then try to roll it, doesthe tire go straight? What happens? The tire triesto roll away in the direction that the tire is leaning. Forthis reason, remember that a vehicle will have atendency to pull or drift to the side with the mostpositive camber. Camber readings should not varymore than 3/4 degree difference from side to side,unless specified by the manufacturer.

Personal Notes


Camber specs are often displayed in this format:

MINIMUM PREFERRED MAXIMUM

These readings tell the technician that the correctsetting (the PREFERRED reading) can vary any-where within the minimum and maximum range,WITHIN THE SPECIFIED SIDE TO SIDE DIFFER-ENCE.

For example:

MINIMUM PREFERRED MAXIMUM +1/4o +1o +1 3/4o

These specifications would indicate that the correctsetting is a positive one degree. It can vary frompositive one-quarter of a degree to positive one andthree-quarters of a degree. Therefore we could usethe following settings, allowing a maximum of 3/4degree side to side difference:

LEFT TIRE RIGHT TIRE+1/4o +1o

+1/2o +1 1/4o

+3/4o +1 1/2o

+1o +1 3/4o

All of these readings are correct, within specifica-tions, and should not cause either tire wear or han-dling problems. However, if we set the vehicle with thefollowing readings,

LEFT TIRE RIGHT TIRE+1/4o +1 1/4o

we would still be within specs (between minimum andmaximum) but we have exceeded the 3/4 degree sideto side difference. This vehicle, while it may not weartires, would probably have a slight pull to the right, dueto the more positive camber on the right wheel.


Camber is adjusted in many ways. One of the morecommon methods is to use spacer shims between theframe and the control arm shaft. As shims are added

or removed, the control arm is movedin or out, thus moving the top of the tirein or out. If the shims are inside theframe, adding shims would move thecontrol arm IN, producing a change incamber toward negative. If the shimsare located Outside the frame, addingshims would move the control arm OUT-WARD, resulting in a positive camberchange. When changing only the cam-ber angle, shim movement must beequal at both the front and rear shaftbolts.

Other vehicles may have the shaftmounting bolts attached to the framethrough slotted holes. In this case,changing camber is achieved by mov-ing the front and rear of the control armequal amounts in the slotted holes.Chrysler products often used an eccen-tric bolt at each leg of the control arm.Camber is adjusted by rotating eachcam bolt an equal amount, and in the

same direction. Some of the other designs can befound in the rear of your alignment specs guide.

Personal Notes


In some cases, the control arm is asymmetric bydesign. Notice that one leg of the arm is in a moredirect line with the ball joint than the other one. Thisis the leg that is used to set camber. The other legis used to set the caster angle.


CASTERThe function of CASTER is to aid proper steeringstability. Caster provides this function by tilting thevehicle's steering pivots (axis) to the front or rear. Thisaxis is an imaginary line drawn through the upper andlower steering pivot points when the vehicle is viewedfrom the side. These pivot points can be upper andlower ball joints on a SALA suspension system. Onconventional strut equipped vehicles, they are the lowerball joint and the upper bearing plate. On vehiclesequipped with king pins, the king pin serves as the pivotpoint.

As viewed from the side, this imagi-nary line drawn through the steer-ing pivots compared to true verti-cal is CASTER. If the top of thisline is tilted toward the rear of thevehicle, the caster is POSITIVE. Aforward tilt of the line is NEGA-TIVE. If the line is NOT TILTED,the caster is ZERO.

Caster's main function, DIREC-TIONAL STEERING STABILITY,is achieved through the loading ofthe spindle. If the caster angle ispositive, when the front wheels areturned the spindle on the inside ofthe turn will move in a slightly down-

ward direction. At the same time the spindle on theoutside of the turn moves slightly upward. Since the tireand wheel are between the spindle and the road sur-

PositiveCaster

Zero Caster Negative Caster

Personal Notes


face, the spindle cannot move downward. The result isthe spindle that is trying to move downward will lift thechassis upward, therefore increasing the load on thatspindle. Since spindles seek equal load, the vehicleautomatically tends to steer toward straight ahead ifcaster angles are equal on both sides. This tendencyto return to the lowest chassis position, straight ahead,provides steering wheel return and is considered to bethe position of greatest stability. Increasing castertoward positive will increase directional stabilityand increase steering effort. Decreasing casterwill reduce directional stability and decrease steer-ing effort.

Caster is generally not a tire wearing angle; it isused to help stabilize the vehicle and make turningaway from straight ahead easier or harder. If a vehicleis equipped with manual steering, the caster anglewill usually be quite small, possibly even slightlynegative, to make steering easier. However, if thevehicle has power-assisted steering, the caster willnormally be set more positive, to give the driver more"FEEL" to the steering. The added positive casterprovides more force for the power steering to workagainst and therefore increasing the stability.

Caster is adjusted several ways. If the vehicle hasshims at the upper control arm, adding a shim to thefront and removing a shim of equal thickness from therear will change the caster, without effecting camber.

If the control arm is mounted in slotted holes, the frontand rear of the arm are moved in opposite directionsto adjust caster without changing camber.Likewise, on those arms having eccentric cam bolts,turning the two cams equally in opposite directionswill change the caster without affecting the camber.Earlier, it was noted that the strut rod was quite oftenused as a caster adjuster. The strut rod is connectedforward or rearward to the frame. If connected forward,lengthening the rod (through adjusting nuts), will movethe lower ball joint toward the rear of the car resultingin a decrease in caster. Shortening the rod will changecaster in the positive direction.

DUAL ECCENTRIC CAMS

ADJUSTABLE STRUT ROD

ADJUSTABLE BALL PIN


SIMULTANEOUSCASTER and CAMBER

CHANGESo far, you have read about changing one angle orthe other, without affecting the other. What aboutthose cases where both camber and caster must becorrected. Is it necessary to adjust first, the caster,and then the camber. Could it be done in only one stepinstead of two?

There is an old "Rule of Thumb" that many alignmenttechnicians have used. It says that placing a 1/8"shim at one end of a control arm will change camberby 1/4o and caster by 1o. That means that, adding or

subtracting 1/8" shim to both the front andrear bolts of the control arm will changecamber by 1/2o. Likewise, adding 1/8" shimto one bolt while subtracting 1/8" shim to theother, will change caster by 2o. Let’s see howthis works, when applied to doing both casterand camber.

It is important that you remember that thisformula is only a close approximation ofwhat is really going to happen. The formulais dependent upon the size and shape of thecontrol arm. In fact, this formula has an errorfactor of about 40%. In other words, it willget you close in about 60% of the cars thatyou adjust.

The shim chart ON THE NEXT PAGE showsthe approximate total change achieved incaster and/or camber by using the shimslisted. To achieve the camber changes listedwithout effecting caster, shims of equalthickness must be added or removed.

The shim size listed for caster results in thetotal amount of change listed. To achieve

Dualshimpack

Dual frameslots

Personal Notes


this change the shim size must be split in half andadded to one end and the same amount removed fromthe opposite end. For example, on a vehicle with shimsINSIDE the control arm shaft, to change caster 1o

toward positive without affecting camber would requirea shim change totaling 1/8" be made in the followingmanner:

> Remove 1/16" shim from the front> Add 1/16" shim to the rear


STEERING AXISINCLINATION

(SAI)Earlier you read “WHEN VIEWED FROM THE SIDEOF THE VEHICLE” a line drawn between the wheel’spivot points (ball joints) was called the caster angle.

When this line drawn through the steering pivots isviewed from the front of the car, instead of the side, yousee that the top of the line leans inward, toward thecenter. When this line is compared to true vertical,another angle called the Steering Axis Inclination(SAI) is formed. In simpler terms, the line is the inclineof the steering pivots. When SAI (measured in de-

grees) is measured and used withthe camber angle it becomes a veryimportant diagnostic tool. The anglethat is formed by including the cam-ber angle is logically called the IN-CLUDED ANGLE. To include thecamber angle, we must ADD thecamber angle if positive or SUB-TRACT the camber angle if nega-tive. For example, if the SAI is 13.0o

and the camber is +0.5o the Includedangle is 13.5o. Another example;12.0o SAI and -1.25o Camber resultsin 10.75o Included Angle.

When compared at ground level, thedistance between the SAI line (drawn

through the steering pivots) and the tire centerline iscalled SCRUB RADIUS. When the scrub radius istoward the inside of the tire tread, the vehicle has aPOSITIVE SCRUB RADIUS. When the scrub radiusis toward the outside of the tire tread, the vehicle hasa NEGATIVE SCRUB RADIUS.

By altering the SAI angle, which changes the ScrubRadius, the vehicle handling can be designed tobetter suit driver needs.

Personal Notes


Vehicle engineers use these angles to design "DriverFEEL" into the vehicle. They can compensate fordownsized compacts, heavy luxury cars, high per-formance cars or any other desirable characteristic.

When diagnosing customer complaints related to steer-ing feel, check wheel and tire size. Wider wheels andlower aspect ratio tires can increase scrub radius andtherefore alter the perceived steering feel. Thesechanges can alter the handling characteristics of thevehicle, causing wandering or weaving as variousroad conditions are encountered.

Another function of SAI is to help provide dy-namic stability (when the vehicle is in motion)and steering wheel return. You may have no-ticed when you release the steering wheel in aturn, the vehicle tries to return to straight ahead.Also, when turning the steering wheel, one sideof the vehicle rises and the other the spindlerotates in a straight horizontal line. If the SAI istilted the spindle now goes through a horizontalarc. The high point of the arc is when the wheelsare straight ahead. When steering the wheels,the spindle tries to drop downward in its arc.Since there is a tire attached to the spindle, andthe tire is already touching the ground, the spindlecannot drop. Instead, it pushes up on the knuckle.This causes the lower control arm to push on thespring, which in turn pushes the body up. This, ineffect, causes the vehicle’s center of gravity to risealso. Gravity does not like to have things UP, so it triesto pull the vehicle back down to its stable position.Where is this stable position? At the center of the arc,which is when the wheels are straight ahead! This arcis compounded by any caster angle. With zero caster,the arc is a simple one, with straight ahead beingexactly halfway through the arc. If the caster goespositive, the arc is tilted, so straight ahead is nolonger halfway through the arc. As the wheels areturned, one side drops into the arc, but the other siderises in the arc. This is what causes the “tilting” effectto the car body in a turn. The vehicle is designed witha proper amount of SAI, Caster, and Camber. In a turnand as the vehicle side drops, the caster and SAI


causes the camber to change along with springcompression. This produces a “jacking” effect on thecar to help stabilize it during the turn. Caster and SAIwill help to pull the tires back to straight ahead whenthe turn is completed.

Check SAI very carefully if there are problems withpulling or handling that normal alignment doesn’t

seem to correct. When checking thisangle, it is important to assure that thecamber is adjusted as close to thepreferred setting as possible.

If you look at a steering knuckle on aSALA suspension system, there arethree important connecting points: thehole where the upper ball joint attaches;the hole where the lower ball joint at-taches; and the spindle where the tireattaches. The two holes for the ball jointsare responsible for the SAI angle, andthe spindle is responsible for the cam-ber angle. If you were to draw a lineconnecting these three points, youwould have a triangle. This triangle isthe Included Angle, since we includedSAI and Camber together. If you turn thesteering knuckle, or move it in any way,does the triangle change its shape? Aslong as the steering knuckle is okay, theincluded angle will be correct. What ifthe spindle is damaged or bent? Willthat change the shape of the triangle?What if the upper or lower portion of theknuckle is bent? Any time the IncludedAngle is incorrect on a SALA sus-pension the steering knuckle orspindle is bent.

Is it possible to have incorrect SAI and camber, andstill have the correct Included Angle? Suppose alower control arm was bent in an accident. Would thatchange the SAI? The SAI would become less, sincethe lower ball joint moved inwards. As it moved, itbrought the knuckle along with it, thus tilting the spindle

Personal Notes


downwards. Let’s say that the ball joint moved in by2o. If the original SAI was supposed to be 8o, and theoriginal camber was supposed to be 1o, then theoriginal included angle should have been 9o (8 + 1 =9). By moving outward 2o, the SAI would have beenchanged to 6o. Since the spindle was moveddownwards, the camber would have gone positiveby 2o to a total of 3o. Six degrees SAI plus 3o camberequals 9o. So the included angle is CORRECT,

CAMBER

SAI

INCLUDEDANGLE


POSITIVE CAMBER CHANGESAI REDUCED

INCLUDED ANGLE SAME

POSITIVE CAMBERCHANGE

SAI NOT CHANGEDINCLUDED ANGLE

INCREASED

NEGATIVE CAMBERCHANGE

SAI NOT CHANGEDINCLUDED ANGLE

indicating that the steering knuckle is okay, but theSAI is LESS than specs and the camber is GREATERthan specs.Look at the Diagnosis Chart on the next page. Find therow where SAI is LESS, camber is GREATER, andincluded angle is CORRECT. What does the chartstate as the probable cause?By using this diagnostic chart, and accurately meas-uring the SAI and included angle, you and youralignment machine can solve many of the problemsthat come into your alignment bays, as well as findingextra parts and labor sales.

Complete a thorough under car inspection prior tousing this chart. Replace worn or defective parts andthen use the chart to diagnose bent or damaged parts.

Personal Notes


SAI Diagnostic Reference Chart

Short Arm/Long Arm Suspension System

INCLUDEDSAI CAMBER ANGLE PROBABLE CAUSECorrect Less Less Bent KnuckleLess Greater Correct Bent Lower Control ArmGreater Less Correct Bent Upper Control ArmLess Greater Greater Bent Knuckle

MacPherson Strut Suspension

INCLUDEDSAI CAMBER ANGLE PROBABLE CAUSECorrect Less Less Bent Knuckle and/or Bent StrutCorrect Greater Greater Bent Knuckle and/or Bent StrutLess Greater Correct Bent Control Arm or Strut Tower (out at top)

Greater Less Correct Strut Tower (in at top)Greater Greater Greater Strut Tower (in at top) & spindle &/or Bent StrutLess Greater Greater Bent Control Arm or Strut Tower (out at top)

Plus Bent Knuckle and/or Bent StrutLess Less Less Strut Tower (out at top) & Knuckle &/or Strut Bent

or Bent Control Arm

Twin "I" Beam Suspension

INCLUDEDSAI CAMBER ANGLE PROBABLE CAUSECorrect Greater Greater Bent KnuckleGreater Less Correct Bent "I" BeamLess Greater Correct Bent "I" BeamLess Greater Greater Bent Knuckle


FWD Engine CradleMisalignment

Many front wheel drive vehicles are designed wherethe engine cradle also serves as the attachment pointfor the lower pivots of the suspension system. Thesemodular designs are more cost effective for auto manu-facturers because it allows them to completely as-semble the drive and front suspension system in oneunit. This assembly is bolted to the sub-frame as a unitfrom the bottom of the vehicle. The assembly must beproperly aligned with the sub-frame to assure that frontalignment is maintained.

A closer look at the assembly will show that the innerpivots for the lower control arms are bolted to the

cradle assem-bly. The controlarm is attachedto the spindlethrough thelower ball joint.The strut or up-per pivot is at-tached to theupper end of thespindle and isattached to theupper body viathe upper strutmount at the up-per tower posi-tion to completethe suspensionsteering axis.

FWD EngineCradle

Personal Notes


Since the lower control arm pivots are part of the cradlewhich can move under the sub frame, and the upperpivot is rigidly mounted to the upper strut tower, thealignment of the cradle to sub-frame is critical to wheelalignment. If the cradle is misaligned side-to side,camber and SAI are affected. If the cradle is shiftedforward or rearward, caster will be misaligned.

Typically, if the cradle is shifted to the side the SAI willincrease and Camber will decrease on the side thatthe cradle has moved toward and SAI will decreaseand the Camber will increase on the opposite side.

The Cradle must be aligned prior to making any otheralignment corrections.

Cradle ShiftedToward Right Front

Camber - DecreasedSAI - IncreasedIncl'd Ang - Good

Camber - IncreasedSAI - DecreasedIncl'd Ang - Good


DimensionB

DimensionA

TOEEarlier it was mentioned that SAI helps to establish thescrub radius. This information with other suspensiondata enables engineers to establish vehicle toe speci-fications.

When a vehicle is driven, nor-mal dynamic driving forces try tosteer the wheels away fromstraight ahead. The directionthey steer depends on the scrubradius and suspension design.Toe in or toe out, away fromstraight ahead, is used to com-pensate for dynamic forces andnormal tolerances in steeringand suspension parts.

In the illustration to the left, if youmeasure from the front of onetire to the front of the other tire,you would get dimension “A”. Ifyou measure between the rearof these two tires, you would getdimension “B”. If “A” is smallerthan “B”, then we have toe IN. If“B” is smaller than “A”, you havetoe OUT.

The toe setting is designed to compen-sate for the amount the tires will turnaway from straight ahead. If you adjusttoe incorrectly, the tires will not turnenough, or turn too much. In eithercase, the tires will no longer be goingstraight down the road. If they are notgoing straight, they are being“scrubbed” or scraped against the roadsurface. This will to cause the tires towear out. The rule of thumb is; for only

ToeIn

ToeOut

Personal Notes


Feathered or SawtoothTire wear pattern

Sharp edges point in the directionof the toe problem

(IN - Toe In / OUT Toe Out)

Vehicle'sGeometricCenterline

Individual Front Toe

1/8" incorrect toe, the effect is the same as draggingthe tire sideways 28 feet for every mile driven.If the tire has toe-in, the outside edge of the tire wouldbe worn faster than the rest of the tire. It would alsohave a little “feathering” or Sawtoothwear pattern at each rib in the treaddesign. The sharp edges of the wearpattern will point toward the toe prob-lem. In the case of toe in the sharp edgespoint inward. Just the opposite wouldoccur if the tire had toe-out. This can bemore easily seen if you use your feet torepresent the tires. If you walk with thetoes pointing to each other, how wouldyour shoes wear?

Your alignment machine determineswhere the GEOMETRIC CENTERLINEof the vehicle is and then computes thedistance from the front and rear of eachtire to that centerline.

The reading for each tire is INDIVIDUALTOE. When the individual toe for eachtire is added together, we get a readingcalled TOTAL TOE. This is the specifi-cation given in your guide. If the totaltoe (preferred setting) is 1/8", then eachtire’s individual toe should be 1/16" (1/8"divided by 2).

Each tire must be parallel to each otherand parallel to the vehicle’s centerlinewhen it is rolling down the road. In otherwords, the RUNNING TOE should benear zero.

When adjusting toe, the adjustingsleeves on the tie rod ends are rotated.As the sleeve is rotated, the tie rod as-sembly is lengthened or shortened. If thesteering linkage is behind the spindlecenterline (to the rear of the car), length-ening the tie rod assembly will increasetoe in.


Prior to making individual toe corrections, center thesteering wheel and install a steering wheel lock. Onvehicles equipped with power assisted steering, it willbe necessary to run the engine while centering thesteering wheel.Observe the displayed individual toe readings when

correcting toe. Rotating thesleeve on one side can effectthe reading on the oppositeside if the alignment rack turn-tables do rotate freely. If thereadings on the opposite sidechange during correction,check the centering of thesteering wheel and re-adjustthe toe.

When front individual toe is corrected it is either mea-sured in reference to the vehicle's geometric centerlineor the thrust angle. Referencing to the vehicle centerlinecan result in a cocked steering wheel if the rear axle is

not squared with the vehicle center.Always referencing to the vehiclethrust line will increase your odds ofachieving a straight steering wheel. Ifthe rear toe is adjustable, always makerear toe corrections prior to front cor-rections unless otherwise specifiedby the vehicle manufacturer.

The tie rod ends are attached to thesteering arm, which is either a part ofor bolted to the steering knuckle. Anychanges in camber or caster willchange the position of the steeringarm, and thus change the toe setting.

For this reason, the toe adjustment is ALWAYScompleted AFTER the camber and caster adjust-ments.

Rotate Tie Rod Sleeve to Adjust

Personal Notes


TOE OUT ON TURNS(STEERING GEOMETRY)

As the vehicle goes through a turn, the tires on oneside of the vehicle must go through a different sizecircle than the tires on the other side. The vehicleturns about a common center. This can be illustratedwith lines drawn from the center of each front tire thatmeet with a line drawn between the two rear tires. Thisis the common center. The front tires mustturn on different angles to each other. Thetire that is on the inside of the turn willbe steered a greater angle than thetire on the outside of the turn. Thisresults in the tires being toedout in relation to each other.The amount of toe outeffect will be is deter-mined by the angleof the steering arms.

If we look at thesteering arms, youcan see that theyare both angled in-ward. If we were todraw a line down thecenter of eachsteering arm andthen extend thosetwo lines, we wouldsee that they intersect at the center of the rear axle (orwhere the rear axle would be if the car has indepen-dent rear suspension). This angle, called the ACK-ERMAN ANGLE, places the steering arms in differentportions of a similar arc. We can see that, during a turn,the amount of movement of each arm is NOT equal inthe arc. The steering arm on the inside of the turntravels a greater amount through the arc, thus produc-ing the desired toe out effect. Common

Center


18o

20oTurning RadiusMeasurement

Your alignment specs guide has a column for toe outon turns which is the turning angle. You will see that itcalls for two different readings; one for the insidewheel and one for the outside wheel. When measur-ing toe out on turns, start with the left tire and steer tothe left to the specified angle. Use the turning gaugeon your turntables to measure the turn angle. After youreach that amount of degrees, have someone tell youwhat the reading on the opposite wheel is. It should

be within 1 1/2o of the specification.

To correct turning radius, the bent steer-ing arm must be replaced.

This angle, like SAI and includedangle, is primarily a diagnostic angle.Check this angle when the customercomplains of a tire squeal in a turn, orwhen tire feathering is evident and thetoe setting is correct.

Some imports, notably those fromAsia, have a slightly different method of checking toeout on turns. If you look in your alignment specificationguide for a 1986-88 Hyundai Excel, you will see thatthe turning angle specification for the inside wheel is35 13/16o. The specification for the outside wheel is 291/4o. This vehicle has adjustable full-lock steering.Here, the procedure is to turn the steering wheel asfar as it can in one direction. When it can be turnedno more, read the amount that the inside wheel isturned. If it is not as specified, then go under the carand adjust the steering stop until it is achieved. Notuntil the inside wheel is at the correct amount of turncan the other wheel be read. Replace the steering armif the outside wheel is not within 1 1/2o of specification.

Before measuring toe out on turns, it is important tohave both turning gauges set to zero before you begin,and the toe-in setting should be correct. Also, makesure that your turntable gauges read more than 35o.Many older turntables only went to 35o, and need tobe updated.

Personal Notes


Front Setback


Thrust AngleWe previously discussed front individual toe. Checkthe rear wheels of all vehicles to see if the rear wheelsare parallel to the vehicle’s centerline when drivingthe vehicle. As with front wheels the rear wheel speci-fication allows for the amount of anticipated changewhen the vehicle is in motion.

Measuring rear individual toe is the same as measur-ing the front. The alignment system will calculate anddisplay the readings. It is extremely important that thefront wheels be steered to equal toe values prior tomeasuring rear toe.

The same tire wear conditions thatwe discussed for front toe can existon the rear wheels if rear toe is notadjusted to specifications. In addi-tion to tire wear, the rear wheels de-termine the direction the vehicle willroll. If not adjusted properly the rolldirection can cause the vehicle totrack in a direction that is not parallel

to the vehicle’s centerline.The vehicle’s roll direction isthe vehicle’s THRUST LINE.When measuring the rear in-dividual toe, it is measured in

reference to the vehicle’s centerline(GEOMETRIC CENTERLINE). Byaveraging the values of the individ-ual rear toe and drawing a line per-pendicular to the center of the reartires the THRUST LINE is estab-lished. The Thrust Line comparedto the vehicle’s GEOMETRIC CEN-TERLINE is the THRUST ANGLE.

The Thrust Line is the actual direc-tion that the vehicle will travel when driven straightdown the road. If the Thrust Line is not identical to theGeometric Centerline, the driver must steer to causethe vehicle to drive in a straight line. This results in acocked steering wheel in the direction of the Thrust

GEOMETRICCENTERLINE

THRUSTLINE

ThrustAngle

Personal Notes


Aftermarket Shim

Line. This misalignment of the rear wheels in relation-ship to the vehicle centerline also causes the vehicletracking to be offset (the rear wheels run in a differenttrack than the front). This condition is commonly re-ferred to as “dog-tracking”.

The Thrust Angle should always be near zero. Con-sult the specification guide for manufacturer's recom-mendations. The Thrust Angle is adjusted as the rearindividual toe is adjusted.

Many vehicles have either built inadjustments or an aftermarket ad-justment part is available. On ve-hicles with a fixed rear axle or nonadjustable independent rear sus-pension, look for worn or damagedparts including the axle itself. Wornrear spring mounts can cause therear axle to shift. Rear control armbushings can become worn and al-low the rear axle to shift.

If no worn or damaged parts can bedetected, use the rear thrust angleas the reference when adjusting thefront individual toe. This will compensate for any outof thrust condition and the steering wheel will bestraight when driving the car straight down the road.


GLOSSARYACKERMAN Principle: An alignment principle based on vehicle tread width and wheelbaseupon which turning angle is computed.Active Suspension: A suspension system in which hydraulic actuators add force to thesuspension system to allow compression (Jounce) and extension (Rebound).Alignment: The process of measuring and positioning all wheels attached to a commonchassis.Angle: Two intersecting lines that are not parallel.Arc: Any part of a circle or a curved line.Axial Play: Vertical movement of the wheel and tire assembly when inspecting a ball-joint.Balance: This term is used to describe having equal weight distribution about the circumfer-ence of a wheel and tire assembly.Ball-Joint: A chassis to knuckle connector consisting of a ball and a socket. This configurationallows for simultaneous angular and rotating motion.Bead: Steel wire forming an anchor for individual plies and rim attachment of a tire.Bellows: a Rubber type seal which is folded to allow for a telescopic action. Normally referredto as a bellows boot.Bias Belted: A tire construction type with overlapping plies at 90 degrees with additional beltsformed around the circumference of the tire.Bias Ply: The same type of construction is used on this design as a bias belted, but without thereinforcement belt.Body Roll: The leaning of the vehicle body while cornering.Braking Control: Vehicle stability related to the reaction under all stopping conditions.Bump Steer; A directional change in steering caused by road irregularities. As the suspensionmoves through jounce and rebound, changes in alignment at the front or rear wheels may alterthe vehicle’s directed path.Bushing: A component made of metal or rubber-type material, used to isolate interconnectedmoving parts.Cam Bolt: A bolt and eccentric assembly which when rotated will force components to changea position.Camber: The inward or outward tilt of the wheel at the top and as viewed from the front.Camber Roll: A change in camber brought about by suspension changes while cornering.Caster: The forward or rearward tilt of the steering axis at the top and as viewed from the side.Center Bolt: A bolt that provides centering and attachment of an axle and spring assembly.Centerline Steering: A centered steering wheel while the vehicle is traveling in a straightahead course.Chassis: All major assemblies on a vehicle including suspension, steering, drive-train andframe; everything except the body.Circumference: The total distance around a circle.Coil Spring: Spring steel wire formed in the shape of a coil.Compliance: The ability of an object to yield elastically when a force is applied.Concentric: Two or more components sharing a common center.Conicity: The cone shape that a tire takes through its normal life when inflated and loaded.Contact Area: The total amount of tread surface that contacts the road.

Personal Notes


Control Arm: An arm that is used to attach a spindle or axle to the chassis.Cornering: The ease at which the vehicle travels a curved path.Cradle: The framework of a front wheel drive vehicle that provides the engine mounts as wellas front suspension pivot points for many vehicles.Curb Weight: The overall weight of a vehicle less passengers, luggage, or load.Degree: A unit of measurement to describe an angle.Dial Indicator: An instrument used to measure and display linear displacement. Measurementis displayed on a dial face and the scale is commonly graduated in thousandths.Directional Stability: The tendency for a vehicle to maintain a directed path.Drag Link: A tube or rod used for interconnection between a pitman arm and tie-rodassemblies.Dry Park Check: Inspection of chassis & steering parts with the vehicle at normal ride height.Not in the raised position.Dynamic Balance: This normally refers to the balance condition of a wheel and tire assemblyin motion.Eccentric: See cam bolt.Feather Edge Wear Pattern: An abnormal tread wear pattern where by one side of anindividual tread rib is worn more than the other.Flow Control Valve: Regulates flow output from the power steering pump. This valve isnecessary because of the variations in engine RPM and a need for consistent steering abilityin all ranges from idle to highway speeds.Foot Pound: A unit of measurement used to describe torque force.Four Wheel Steering: The ability of the rear wheels to aid in steering a vehicle for improvedhandling and driving characteristics.Frame Angle: Used to describe a non-level frame.Friction Ball Joint: Outer suspension pivot that does not support the weight of the vehicle.Front Steer Rack & Pinion: Steering system located in front of spindle centerline.Geometric Centerline: A line drawn between the midpoint of the front axle and the midpointof the rear axle.Horizontal: Parallel or level with the plane of the horizon.Hub: The assembly that houses the bearings about which the wheel and tire assembly rotates.Hydraulic Pump: A power driven device generating constant volume and pressure.Idler Arm: An arm and lever assembly used to support and maintain a parallel position with aconventional steering system.Included Angle: The sum of the angles camber and SAI.Independent Suspension: A suspension system that provides an isolated mounting for eachwheel to the chassis.Individual Toe: The angle formed by a horizontal line drawn through the plane of one wheelversus a centerline.Integral Power Assist: A power assist system where the control valve and all major hydrauliccomponents are self-contained.Intersect: The crossing point of two lines.Jounce Travel: A suspension moving up through its travel.Kinetic Balance: The balance condition of a rotating wheel related to force generated in avertical plane.King-Pin: A pin used to attach a spindle to an axle.


Lateral Run-Out: Side-to-side movement with a rotating wheel or tire.Lead: A slight tendency for a vehicle to lead away from its directed course.Linkage: A series of rods or levers used to transmit motion or force.Load Carrying Ball Joint: Outer suspension pivot that supports the weight of the vehicle.Load Range: A system used to describe the service or weight limitations or a tire.MacPherson Strut: A suspension design where spindle, shock, and spring are all oneassembly.Memory Steer: A condition where the wheels, rather than returning to straight ahead, tend toremember and seek a previous position.Millimeter: A unit of linear measurement. One millimeter is equivalent to 0.039 inches.Minute: A unit of measurement used to describe an angle. One minute is equivalent to 1/60thof one degree.Non-Integral Power Assist: A power assist system where the control valve and all majorhydraulic components are not self-contained.Offset: The lateral displacement of a wheel or axle in respect to a centerline.Oscillate: A motion in two directions and at a specific frequency.Out-of-Round: A wheel and tire irregularity in which one or both are not concentric with its axisof rotation.Overinflation: Inflation pressure beyond what is recommended.Oversteer: A characteristic in which a vehicle has a tendency to turn sharper than the driverintends.Parallelogram Steering Linkage: A steering linkage design where if all pivot points areconnected by lines, these lines would be parallel.Passive Suspension: A suspension system which uses springs along with shock absorbersto allow compression (Jounce) and extension (Rebound).Perpendicular: Being at right angles.Pitman Arm: A steering component that provides interconnection between the steering gearsector shaft and the steering linkage.Ply Rating: A method of rating tire strength; not necessarily indicative of the actual number ofplies used.Power Steering: A steering system which incorporates hydraulics to assist in the steering ofthe wheels.Pre-load: A predetermined amount of load or force applied during assembly to preventunwanted play during actual operation.Pressure Relief Valve: Prevents power steering fluid pressure build up beyond a specifiedpoint. When fluid is at the maximum desired pressure the excess is returned to the pumpreservoir.Pull: The tendency for a vehicle to steer away from its directed course.Rack & Pinion Steering Gear: A steering system designed that utilizes a pinion gear meshedwith a rack gear to transmit steering forces to the spindles.Radial Play: Any lateral movement of the wheel and tire assembly when inspecting a ball-jointor king-pin.Radial Ply Tire: A tire construction type with alternating plies 90 degrees to the tire bead.Radius: The distance from the center to the outer edge of a circle.Rag Joint: A type of U joint constructed from a rubberized fabric type material.

Personal Notes


Rear Steer Rack & Pinion: Steering system located in front of spindle centerline.Rebound: A suspension moving down through its travel.Recirculating Ball Steering Gear: A steering gear design that is made up of a worm shaft, ballnut, and two recirculating ball circuits.Returnability: The tendency of the front wheels to return back to a straight ahead position.Road Crown: The slope of a road from its center.Road Feel: Necessary feedback transmitted from the road surface up to the steering wheel.Road Isolation: The ability of a vehicle to better separate road irregularities from the driver andpassengers.Road Shock: An excessive amount of force transmitted from the road surface up to the steeringwheel.Scrub Radius: The radius formed between wheel centerline and steering axis projected loadpoints at the road surface.Setback: The angle formed between a centerline and a line perpendicular to the front axle.Shim: Thin material of fiber or metallic makeup used to take up clearance between two parts.Shimmy: A violent shake or oscillation of the front wheels transmitted up to the steering wheel.Shock Absorber: A suspension component used to dampen spring oscillation.Solid Axle Suspension: A suspension system consisting of one steel or aluminum I-beamextended the width of the vehicle.Short Arm Long Arm (SALA): An independent suspension design incorporating unequallength control arm.Spindle: A component on which a wheel and tire assembly is mounted and rotates.Stability: The tendency of a vehicle to maintain a directed course.Stabilizer Bar: A steel bar used to minimize body roll.Steering Arms: A steering component which provides interconnection between the outer tie-rod and spindle.Steering Axis Inclination: The angle formed by an imaginary line drawn through the steeringaxis versus vertical. Viewed from the front.Steering Gear: A mechanical device used to convert the rotary motion at the steering wheelto a lateral motion.Steering Geometry: See Alignment.Steering Knuckle: A forged assembly which typically includes: the spindle, steering arm andsteering axis pivot points.Steering Shaft: A tube or rod which interconnects the steering wheel to the steering gear.Steering Wheel Play: Any abnormal play or movement that does not result in movement at thefront wheels.Strut: Any support used between two parts.Suspension: An assembly used to support weight, absorb and dampen shock, help maintaintire contact, and proper wheel to chassis relationship.Suspension Height (Ride Height): The specified distance between one or more points on avehicle to the road surface.Thrust Angle: The angle formed by thrustline and geometric centerline.Thrustline: Average rear toe added together and divided by two. The direction the rear rolls.Tie Rod Assembly: The outer most assemblies on a parallelogram steering linkage. Theseassemblies are attached to the drag link and steering arms.Tie Rod End: The ball and socket assembly of a tie rod.


Tie Rod Sleeve: A threaded tube that provides connection and adjustment of a tie rodassembly.Tire Force Variation (Radial Force Variation): A tire irregularity in which there is a differencein radial stiffness about the circumference of the tire.Tire Wear Pattern: The design developed on the tread surface from abnormal wear.Toe: The comparison of a horizontal line drawn through both wheels of the same axle.Turning Angle: The difference in the turning angle of the front wheels in a turn.Torsion Bar: A spring steel bar used in place of a coil spring. Suspension is provided throughits resistance to a twisting or torque effort.Torque Steer: The effect that acceleration or deceleration has on the steering of the frontwheels.Tracking: The interrelated paths taken by the front and rear wheels.Treadwidth: The dimension as measured between the centerlines of the wheels on the sameaxle.Treadwear Indicators: Ridges molded between the ribs of the tread that visibly indicate a worntire.Underinflation: Air pressure below that which is specified.Understeer: A characteristic in which a vehicle has a tendency to turn less than the driverintends.Unit Body (Uni-Body): A design that incorporates both body and frame as a unit.Vertical: Being exactly upright or plumb.Vibration: To constantly oscillate at a specific frequency.Waddle: The lateral movement of a vehicle usually caused by some type of tire or wheelimperfection.Wander: The tendency of a vehicle to drift to either side of its directed course.Wheel Base: The dimension as measured between the center of the front and rear axles.

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