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    • Chs 2 & 3
    • Ch 4 – Engine Basics
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      • Ch 7 Powertrain Review Questions
    • Ch 9 – Cranking Starting Systems: Heavy Duty Truck Systems
    • Chapter 11 Diagnosis and Repair of Electronic Circuits
    • Ch 16 – Standard Transmission
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    • Chapters 10-13
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    • Ch 11 – Engine Coolant Systems Review Questions
    • Ch 12 – Engine Breathing
    • Ch 13 – Engine Retarders
    • AC
    • Ch 23 Truck Axles
    • Ch 25 Steering & Alignment
    • Ch 28 Truck Brake Systesm
    • Ch 29 – Hydraulic Brakes & Air over Hydraulics
    • Ch – 31
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Ch 25 Steering & Alignment

Power-assisted steering
On highway vehicles is required to function with full mechanical redundancy in the event of a loss of power-assist system
Full power steering system
Found on some off highway equipment. This equipment often uses hydrostatic steering: in the event of loss of hydraulic power, this will result in no asteering capability
Steering System Components
steering wheel, steering column, steering gear, and sterring linkages that actually move the steering tires
Typical size of a heavy-duty trucks
22 to 24 inches
U-joints should be lubed in the same manner as those in the drive shaft assembly. It should come out all four trunnion journals.
Many steering column related problems are caused by U-joints failures
Steering Gear
A gearbox that both multiplies steering input torque and changes its direction
Three general categories of heavy-duty steering gears
Worm and sector shaft; Recirculating ball and Rack and pinion
Pitman Arm
Is a steel lever, spline attached to the sector (output) shaft of the steering gear.
The end of the Pitman arm moves through an arc with the sector shaft center forming its center.
The Pitman arm functions to change the rotary motion of the steering gear sector shaft into linear motion.
Drag link
Is a forged rod that connects the Pitman arm to the steering control arm
The drag link is connected at each end by ball and socket joints. Ball and socket joints help isolate the steering gear and Pitman arm from axle motion
When the drag link is moved in a linear direction, the steering control arm moves the steering knuckle, which changes the angle of the steering knuckle spindle
Steering Control Arm
Connects the drag link to the steering knuckle on the driver side of the vehicle
Kingpins
The linkage pin used in a steering knuckle that permits the assembly to pivot
A steering control arm is attached to the upper portion of the left side steering knuckle and Ackerman (tie-rod) arms are attached to both left and right steering knuckles
A kingpin can be either tapered or straight. Tapered pins are drawn into the axle center and secured by tightening a nut at the upper pin end. A straight kingpin is secured to the axle with tapered draw keys that bear against flats on the pin
Zerk-type grease fittings are used to lubricate steering knuckles
The steering control arm is fastened to the upper knuckle of the steering knuckle with a key and nut. The Ackerman arm is fastened to the lower knuckle in the same way.
A ball joint and socket joint are manufactured using forged steel ball with a threaded stud attached to it.
Ball and socket joints are used in the steering linkage to accomodate motion between the axle and the frame rails that results when the front axle springs flex and do so without affecting steering.
Ackerman Arm
Or tie-rod arm is a means used to transfer and synchronize steering action on both steer wheels on a steering axle. One end of an Ackerman arm is keyed and bolted to the lower portion of the steering knuckle. The other end is taper bored to allow a tie-rod ball stud to be clamped to it
Tie-rod
Transfers steering motion from the steering gear side of the chassis to the opposite side by means of an adjustable rod, forcing the steering knuckles to act in unison
A tie-rod assembly consists of a cross tube and two tie-rod ends.
The tie-rod ends are ball sockets that connect to the Ackerman arms on each steering knuckle
Tie-rod ends are ball sockets that connect to the Ackerman arms on each steering knuckle.Each tie-rod end is threaded onto eiher end of the cross tube to connect tit to tapered sockets in the Ackerman arms.
One side of the tie-rod has left-hand threads, and its oppostie side has right-hand threads
The length of a tie-rod assembly defines the toe setting. Its length is determined by the postion of the tie-rod ends
A front end that is properly aligned will result in
* Easier steering
* Longer tire life
* Directional stability
* Less wear on front-end components
* Better fuel economy
* Increased safety
Toe
The tracking angle of the tires from a true straight-ahead track
Toe-in
When the fronbt end of the tire points inward toward the vehicle
Toe-out
When the front of the tire points outward from the vehicle
In extreme cases of toe-in and toe-out, feathered edges develop on the tread across the entire width of the tread face of both radial and bias-ply tires
Too much toe-in produces scuffing or a featheredge along the inside of the tires. Excessive toe-out produces a similar wear pattern along the outside of the tires
Most radial steering tires are set with aero toe angle and bias-ply tires are set with a fractional toe-in
Steering tires are designed to use a positive camber angle setting
Camber
is a measure of the angle a wheel leans away or toward the frame
A positive camber setting is used to help compensate for the slight tendency of steering tires to toe-out when vehicle is moving
Toe-in setting is 1/16 inch+ – 1/32 inch (1.6 =- 0.8mm). it depends on whether radial or bias-ply tires
Adjustment of toe angle or dimension requires lengthening or shortening the tie-rod dimensions. Loosen the tie-rod end clamp bolts and then rotating the cross tube
When measuring toe angle, the front suspension should be neutralized. To neutralize the suspension roll the vehicle back and forth about a half vehicle length. This relaxes the front suspension and steering linkages
Caster
is the forward or rearward tilt of the kingpin centerline when viewed from/ the side of the vehicle
Positive caster indicaTES THAT THE KINGPIN IS TILTED REARWARD
NEGATIVE CASTER INDICATES THAT THE KINGPIN IS TILTED FORWARD
Caster settings generally affect steering performance:
Too little caster can cause wheel instability, wandering and poor wheel recovery:
Too much caster can result in hard steering, darting, oversteer and low speed shimmy
Recommended Caster Settings:
Tandem Drive axle: 1/2 to 1 1/2 degrees positive
Single drive: 1 1/2 to 2 1/2 degrees positive
No more than 1/2 degree difference between the left and right wheels
Positive caster on the left wheel should not be greater then on the right
Kingpin inclination (KPI)
is the inclination of the steering axis to a verical polane that is the equivalent of steering axis inclination (SAI) in automobiles front ends
Ackerman Geometry
is the means used to steer a vehicle so that the tires track reely during tires
oversteer
is an overresponse to steering input, which resutls in vehicle yaw
understeer
is the underreponse to steering input. most often calsuing stgeering slip at high speeds
Dog-tracking
a misalignment condition in which the rear wheels of a truck run on a different track linethat the front steering wheels, creating a thrustline irregularity

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