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Ackerman effect is a wheel alignment term and it can be found in riding garden tractors or lawn mowers to large class 8 trucks and beyond. It is machined or made into the steering mechanism and works sort of in a cam type fashion when the steering is turned from straight ahead. The exact portion of the steering mechanism that contains this varies from vehicle to vehicle.An example location is: Most truck straight front axles normally has the Ackerman effect machined into the steering arms (better described as the Ackerman arms) per the location of the holes where the tie rod ends attach and/or the bend in those arms. The function of Ackerman Effect is to cause the steer tires to toe out on turns, preventing tire scrubbing during such turns. |
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Camber is the sideways tilt of the tires on a particular axle (on a perfectly level surface). Most all vehicles have some camber on the steer tires. Steer axle camber is important to make the vehicle hold a straight line on an inclined surface-namely the crowning effect of all paved as well as unpaved roads (crowning the roadway helps with water drainage). Positive camber is also used to help prevent straight axles under load from causing excessive tire wear from sway. Camber measurement is in degrees. |
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Caster as refered to in car and truck wheel alignment is the tilt of the steering knuckle or spindle forward or rearward as opposed to straight up and down. Caster is almost always positive (the tire is forward at the bottom of the tire and rearward at the top). Power steering uses about 3 times as much caster as manual steering because the function of caster is purely steering stabilization (at the steer ahead position). Power steering needs more stability hence the higher amounts. High caster tends to stiffen steering hence the lower amounts on manual steer vehicles. Caster looses all it's functionality when the steer tires are turned away from steer ahead position very much at all. Caster measurement is in degrees. Caster is often a misunderstood angle where used on motor vehicles. |
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Cross caster is the difference in each tire's caster amount on any one axle. If the caster measurement on one tire is 3.5 degrees and the other tire's measurement is 3.0 degrees then the cross caster amount is 0.5 degrees.In the USA and Canada etc., positive cross caster is when the higher individual caster reading is on the right side and negative cross caster is when the larger individual caster reading is on the left side. Generally cross caster amounts of 0.5 degrees and larger will cause a drift to the right or left in the front end, left if the cross caster is positive and right if the cross caster is negative. Cross caster can be used as a beneficial tool if trying to make larger vehicles such as a motorhome or heavy truck hold the road when cold bending the steer axle to set camber is prohibitive. |
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With the vehicle setting on a level floor, driveline angles and angles of the engine/transmission and rear axle(s) can be measured then adjusted to relieve any driveline vibration that may exist. Measuring and adjustment can be simple or get quite involved, especially if the engine/transmission angle must be changed to cause the driveline angle cancellation to come into specs. While each u-joint has it's own working angle that must be within a certain amount for proper needle bearing rotation, u-joint angle cancellation is the most important setting to cancel out driveline vibrations. The engine/transmission and rear axle(s) must also stay within a certain range for proper lubrication of internal parts. Refer to the ebook for a complete explanation of driveline angle setting. |
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Driveline vibrations can come from a variety of sources. A spread or loose yoke or bad u-joint can cause a driveline vibration but the driveline angles can be at fault causing it's own vibration and/or u-joint failure. Spread yokes usually come from over torquing them (beyond their capability) and/or by driveline shock. Some other reasons for driveline vibration is a twisted or bent driveline or imbalance of a driveline. Medium and heavy trucks have more than their fair share of driveline problems because of the heavy loads they carry and the engine torque that a large diesel engine can develp. |
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Included angle, or IA as it is refered to in wheel alignment terms, is an angle formed by the SAI (or steering axis inclination) combined with the camber amount. See steering axis inclination (or SAI) for more details. |
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Individual toe comes into play on cars or pickups as well as some motorhomes and buses if they are equipped with independent front suspension. These vehicles have two adjustable tie rods on the same mechanism, one for the left tire and one for the right tire. It is very important to set them equally and the resulting settings end up as the prefered total toe amount. See toe and total toe for more specific explanations of these terms. If improperly set, it is theoretically possible for individual toe to upset other wheel alignment angles and effects such as Ackerman effect and SAI to a certain degree. Unlevel steering wheels, decreased cornering quality, excessive tire scrubbing and unequal full turns left and right are also some of the ill effects. |
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There are generally two kinds of adjustment possible on medium and heavy truck clutches. One is adjustment at the clutch linkage for free travel and the other is internal adjustment on the pressure plate for proper throwout bearing/clutch brake/pressure plate clearance. Internal adjustment sometimes require special tools but with other clutches regular hand tools is enough. Internal clearance between the throwout bearing and clutch brake is usually about 1/2 inch. Details on internal and external truck clutch adjustment are included in the ebook. |
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Kingpin has two definitions as far as a heavy trailler truck is concerned but on a RV (motorhome), bob medium truck or bus it generally has only one meaning. The pin on the semi trailer that the fifth wheel latches to is called the trailer kingpin. The other meaning of kingpin is refering to the large pin that holds the spindle onto the axle and allows for side to side rotation of the spindle. It is vital that slack be kept at a minimum for proper wheel alignment therefore proper greasing once a week or every other week using regular grease (not synthetic) is recommended in the ebook. |
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On the steer axle, when an imaginary line is drawn through the exact center of the tire and another imaginary line is drawn through the exact center of the pivot point. The measurement from one line to the other at the point of intersection of both lines with the surface the tire is setting on depicts scrub radius. When the scrub radius amounts vary from one side of a particular axle to the other, a pull or drifting results directed toward the side with the greatest amount of scrub radius. One low pressured tire, mismatched tires, one tire worn more than the other tire, installing radically shorter tires on a vehicle & manufacturing flaws resulting in only one tire on an axle being shorter than the other are examples of scrub radius problems. Tire scrubbing (excessive tire wear) results from excessive scrub radius. |
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Steer axle setback is measured the exact same way as thrust angles(see thrust angles) except is is related only to the steer axle instead of the drive axles. Excessive setback is usually a result of either trauma or slippage to the front suspension and/or frame. Excessive setback upsets a myriad of other wheel alignment angles making for a poor handling vehicle with excessive steer tire wear. |
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The ebook offered explains heavy duty steering gear adjustment and some repairs any mechanically inclined person can perform with a little guidance. It includes older steering gears as well as newer steer gears and some light truck steering gears. It explains timing and attachment of various components like lower column shafts and pitman arms for gears such as TRW Ross and Shepard Steering gears. Some insight to internal workings are explained inside these gears, adjustible drag links and their relation to steering and steering gears as well as adjustment procedures, explanation of control arm and control arm keys and their relation to steering gear position are some of the text included. |
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A loosely used suspension, steering and wheel alignment term which describes the pivoting portion or area of the steer axle which is refered to as spindle & kingpin in most medium/heavy truck shops and ball joints etc. on some rear wheel drive cars and trucks. |
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The slipping back and forth portion of the lower column shaft especially on large vehicles like motorhomes, buses, medium duty trucks and heavy duty trucks. The slip joint allows movement in the lower column shaft without periodic binding from cab or frame movement or flexing. These joints can be greased on some vehices but others have removed the zerts then sealed them (supposedly from outside weather and dust). A seized up slip joint results in potentially dangerous hard steering while wear in a slip joint results in excessive slack at the steering wheel. |
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A term used on this site meaning any item not critical to travel but makes travel more enjoyable or easier. |
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Travel essentials entail items critical to travel where extended stays or time is encountered, or critical travel related information is available in the medium truck, heavy truck, bus or motorhome steer tire wear, wheel alignment, suspension & steering ebook. Our Basic Vehicles & Equipment Operating Systems & Components ebook is a more recent addition of sometimes critical travel related or equipment related info. |
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The term thrust angle(s) refers to the angle formed by a straight imaginary line drawn through the exact center of the rear axle and another imaginary line drawn through the exact center of the vehicle itself (front to rear). Zero degrees thrust angle is when the two lines are at a perfect 90 degrees with each other. As the angle formed by the two lines depart from 90 degrees, the amount of departure (in degrees) is the amount of thrust angle either positive (toward the right side of the vehicle) or negative (toward the left side). |
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Draw an imaginary line through each tire and wheel from front to back. Zero toe is when the distance between these two lines are equal measured at the front tread of the tires and again at the rear tread of the tires. Positive toe is when the measurement is closer at the front and negative toe is when the measurement is closer at the rear. Toe is measured in inches, millimeters or degrees. Degree measurements are the most accurate for several reasons. Toe type wear gets pretty involved especially on large vehicles such as motorhomes or medium & heavy trucks because it readily mixes with other wheel alignment angle wear confusing many persons. Toe type wear of all types is discussed in depth in the ebook. |
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Total toe refers to the overall toe setting on any one specific axle (see toe for explanation of toe measurement). It encompasses both individual toe settings where an independent front suspension is concerned. For straight front axles where individual toe is only used for diagnostic reasons, total toe settings alone are possible by adjusting the one tie rod located on such vehicle. Total toe amounts are very critical for good tire performance and wear, so generic toe amounts found in many wheel alignment spec guides are not nearly exact enough and should be used for a guide to limitations only. |
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