Steering and Alignment

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Steering and Alignment
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Objectives

• Identify the components of the steering system
  of a heavy-duty truck.
• Describe the procedure for inspecting front
  axle components for wear.
• Explain how toe, camber, caster, axle
  inclination, turning radius, and axle alignment
  affect tire wear, directional stability, and
  handling.

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INTRODUCTION

• The steering system in a heavy-duty truck is
  expected to deliver precise directional control
  of the chassis at both gross and unloaded vehicle
  weight. It has to be able to minimize driver
  effort while retaining some road feel. Truck
  steering systems can be either manual or
  power-assisted.

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Manual Steering Gear Components.
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STEERING GEAR

• The steering gear is a gearbox that both
  multiplies steering input torque and changes its
  direction. Truck steering systems do not use rack
  and pinion-type steering gear. There are two
  general categories of heavy-duty steering gears
• Worm and sector shaft
• Recirculating ball

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Components

• Steering gearbox is connected to the Pitman Arm
• Pitman Arm is connected to the Drag Link
• Drag Link is connected to the Steering Arm
• Steering Arm is connected to the Steering Knuckle
• Steering Knuckle is mounted to the axle and has
  the Ackerman arm attached to it
• Ackerman arm has a tie rod cross tube connected
  to it that goes to the other Steering Knuckle

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PITMAN ARM, DRAG LINK
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STEERING KNUCKLE
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Tapered knuckle pin
straight knuckle pin
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FRONT-END ALIGNMENT
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Measuring Toe
1/16 inch or- 1/32 toe in Always the final
adjustment
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Deep Drop Tie-Rod Ends
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CASTER
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Recommended Caster Settings

• Tandem drive axle 1/21 1/2 degrees positive
• Single drive 1 1/2 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 than on the right.

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Measuring frame angle
Positive frame angle (forward tilt) Should
be subtracted from caster spec
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Measuring Caster
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Camber/Caster Gauges
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Caster Shims
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Checking Steer Axle Twist
Compare left to the right
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Camber
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Kingpin Inclination
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CAUTION

• Recheck the toe setting after any change in
  caster or camber angle.

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Turning Angle or Radius
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Shop Talk

• The power steering gear pressure relief valve
  should open just before the steering stop screw
  contacts the axle stop. You may have to adjust
  the power steering gear so that power-assist
  stops approximately 1 degree before the steering
  stops contact. Failure to do this will result in
  slamming of the steering stops on full lock turns.

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ACKERMAN GEOMETRY
Intersect at the same point, not parallel
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In a toe-out condition on turns, the inside wheel
turns at a greater angle than the outside wheel
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AXLE ALIGNMENT
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Axle Offset
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ELECTRONIC ALIGNMENTSYSTEMS
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BEAM ALIGNMENT SYSTEMS
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SENSOR AND COMPUTER ALIGNMENT SYSTEMS
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A Hunter WinAlign display screenshowing an
initial analysis of alignment data.
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WinAlign automatically calculatesthe correction
for the technician.
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Trailer Tracking
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Trailer Axles
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INSPECTION PROCEDURE

• When a steering problem is reported,
  systematically inspect the vehicle steering
  system, front and rear suspensions, and trailer
  suspension. In most cases, a road test will be
  required, but never take a truck out onto a road
  until you are sure it is roadworthy. If a
  reported problem occurs only when the vehicle is
  loaded, you should test drive the vehicle loaded.

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WARNING

• When a vehicle is operated at temperatures
  below 30F (-1C) with SAE 90 weight oil in a
  manual steering gear, it can turn to a
  grease-like consistency, resulting in stiff,
  sluggish steering. This can compromise accident
  avoidance maneuvers because of slow steering
  response. When operating in temperatures
  continuously below 30F (-1C), install a
  lighter oil in manual steering gear, such as SAE
  75 weight oil.

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WARNING

• All steering mechanisms are critical safety
  items. A vehicle should be deadlined
  (out-of-service OOS report) when a defect is
  reported. It is essential that instructions in
  the service literature are adhered to. Failure to
  observe these procedures may cause loss of
  steering with life threatening results.

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Steering Knuckle Vertical Play.
0.04 max
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Kingpin Upper Bushing Free Play.
0.015 max
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Kingpin Lower Bushing Free Play.
0.015 max
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Kingpin Upper Bushing Torque Deflection.
0.015 max
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Tie-Rod Inspection
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Shop Talk

• Tighten the nut to the minimum torque first
  and then continue tightening to align the cotter
  pin hole. Verify that the torque does not exceed
  the maximum specification. If it does, replace
  the nut.

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Wheel Bearing Inspection
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Adjusting Knuckle Vertical Play
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Steering Knuckle Disassembly
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Kingpin Removal
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CAUTION

• Never use heat on any steering system
  components, because it removes the temper and
  destroys the components.

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Kingpin Bushing Replacement
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Shop Talk

• Always replace the kingpin if there is
  evidence of surface damage. When you replace
  kingpins, it is good practice to replace the
  bushings at the same time. Some bushings must be
  reamed after installation to fit the kingpin.

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Align the draw key hole with the knuckle pin flat.
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UNITIZED STEER AXLES

• Unitized axles have recently been introduced
  to reduce and sometimes eliminate many of the
  maintenance procedures that we have just
  outlined. Parts include unitized wheel hubs,
  integrated seals, and integrated brake spiders.

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MANUAL STEERING GEARS(Worm Roller)
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RECIRCULATING BALL GEARS
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MANUAL STEERING GEARTROUBLESHOOTING
Overcenter position
Backlash area
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Worm Shaft Preloads

• Two types of preloads are used worm bearing
  preload and total mesh preload. The worm bearing
  preload is end-to-end pressure on the worm shaft
  and its bearings. The total mesh preload is the
  result of the combined pressure of the sector
  shaft gear acting on the worm gear and the worm
  bearing preload.

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Measuring and Adjusting Preloads
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Exploded view of a typical recirculating
ball-type manual steering gear.
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Shop Talk

• Do not final torque the screws immediately.
  Rotate the worm shaft assembly with one hand
  while slowly tightening the worm cover screws
  with the other hand. This prevents damaging the
  bearings if the initial shim pack thickness is
  inadequate.

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Full Mesh Preload Adjustment
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Backdrive Check

• The steering gear should turn smoothly,
  whether operated by the steering wheel by means
  of the input shaft, or in reverse, by the front
  wheels acting on the steering linkage through to
  the sector shaft in the steering gear. Reversing
  steering by making the usual output path the
  input path is called backdrive. Backdrive is an
  important factor in proper wheel recovery.

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Centering the Steering System
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Shop Talk

• If caster adjustment is required, it should
  be done before centering the steering system.

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Centering Procedure
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CAUTION

• The Pitman arm should not be removed from the
  sector shaft to center the steering. This can
  dangerously affect the steering geometry.

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HYDRAULIC OPERATION

• The driven end of the worm gear (called a
  ball screw in power steering gears) rotates on a
  ball bearing contained in the valve body.
  Hydraulic oil under pressure enters and exits the
  power steering gear by means of hydraulic lines
  connected to threaded ports in the valve body. A
  pressure relief valve contained in the valve body
  prevents overpressurization of the power steering
  gear.

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POWER-ASSIST STEERINGSYSTEMS(RECIRCULATING BALL
GEARS)
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POWER STEERING PUMP
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Flow Control and Pressure Relief Valves
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TRW/Ross Steering Gear
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Operation
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Shop Talk

• Power steering gear is almost never
  field-rebuilt in todays truck shops. The reason
  is both the critical role steering gear plays in
  vehicle safety and the need to have specialized
  equipment to properly bench test steering gear.
  The function of the technician is to diagnose
  system malfunctions and replace a power steering
  gear with a rebuilt exchange unit when necessary.

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Shop Talk

• A power steering analyzer is the preferred
  method of assessing the performance of a
  hydraulic power-assist steering circuit. The
  power steering analyzer consists of hoses,
  quick-release couplers, a flow meter, pressure
  gauge, and flow control valve.

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Equipment for testing hydraulic supply system.
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CAUTION

• A malfunctioning pressure relief valve might
  not relieve pump pressure, and closing the
  shutoff valve could result in severe pump damage
  or rupture of high-pressure hoses. Constantly
  observe the pressure gauge when closing the
  shutoff valve. If pressure rises rapidly or
  appears to be uncontrolled, do not completely
  close the valve before inspecting the pump and
  pressure relief valve.

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Shop Talk

• It is important that the flow be checked at a
  normal operating temperature and with a load on
  the front axle. Inadequate flow will cause
  binding and uneven or intermittently hard
  steering.

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RACK AND PINION STEERING
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RACK AND PINION PRINCIPLE
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ADVANTAGES

• Rack and pinion steering is simple. There are
  fewer components, fewer pivot points, and fewer
  potential wear points all this results in lower
  maintenance costs. The simplicity of the system
  also translates into a 30 percent reduction in
  total steering system weight. Because of the rack
  and pinion system layout, the steering column no
  longer restricts engine compartment access

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ELECTRONICALLY VARIABLE STEERING
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LOAD-SENSING POWER STEERING
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Summary

• Improper steering adjustments and front-end
  alignment can lead to suspension and tire wear
  problems.
• A properly aligned front end results in
• easier steering
• increased tire life
• directional stability
• less wear and maintenance on front-end
  components
• better fuel economy
• increased safety

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Summary (cont.)

• Ackerman geometry provides toe-out on turns,
  permitting tires to roll freely during turns when
  each travels through a different arc.
• Axle alignment measurements can be taken in a
  number of ways. Tram gauges and measuring tapes
  may be used, as can light or laser beam alignment
  systems with computerized sensors and analysis.

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Summary (cont.)

• Steering axle components should be inspected
  and lubricated routinely on a preventive
  maintenance schedule.
• Two general types of manual steering gear are
  used in heavy-duty trucks. They are the worm and
  sector shaft type and the recirculating ball and
  worm type.
• Truck rack and pinion steering systems were
  introduced in 2007. They provide better road
  feel, resulting in reduced driver fatigue, over
  conventional steering gear systems.