Steering and Alignment

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.

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.

Manual Steering Gear Components.

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

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

PITMAN ARM, DRAG LINK

STEERING KNUCKLE

Tapered knuckle pin straight knuckle pin

FRONT-END ALIGNMENT

Measuring Toe

1/16 inch +or- 1/32 toe inAlways the final adjustment

Deep Drop Tie-Rod Ends

CASTER

Recommended Caster Settings

• Tandem drive axle: 1/2–1 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.

Measuring frame angle

Positive frame angle (forward tilt) Should be subtracted from caster spec

Measuring Caster

Camber/Caster Gauges

Caster Shims

Checking Steer Axle Twist

Compare left to the right

Camber

Kingpin Inclination

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

Turning Angle or Radius

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.

ACKERMAN GEOMETRY

Intersect at the same point, not parallel

In a toe-out condition on turns, the inside wheel turns at a greater angle than the outside wheel

AXLE ALIGNMENT

Axle Offset

ELECTRONIC ALIGNMENTSYSTEMS

BEAM ALIGNMENT SYSTEMS

SENSOR AND COMPUTER ALIGNMENT SYSTEMS

A Hunter WinAlign display screenshowing an initial analysis of alignment

data.

WinAlign automatically calculatesthe correction for the technician.

Trailer Tracking

Trailer Axles

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.

WARNING: When a vehicle is operated at temperatures

below 30°F (−1°C) 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 30°F (−1°C), install a lighter oil in manual steering gear, such as SAE 75 weight oil.

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.

Steering Knuckle Vertical Play.

0.04” max

Kingpin Upper Bushing Free Play.

0.015” max

Kingpin Lower Bushing Free Play.

0.015” max

Kingpin Upper Bushing Torque Deflection.

0.015” max

Tie-Rod Inspection

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.

Wheel Bearing Inspection

Adjusting Knuckle Vertical Play

Steering Knuckle Disassembly

Kingpin Removal

CAUTION:

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

Kingpin Bushing Replacement

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.

Align the draw key hole with the knuckle pin flat.

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.

MANUAL STEERING GEARS(Worm + Roller)

RECIRCULATING BALL GEARS

MANUAL STEERING GEARTROUBLESHOOTING

Overcenter position

Backlash area

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.

Measuring and Adjusting Preloads

Exploded view of a typical recirculating ball-type manual steering gear.

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.

Full Mesh Preload Adjustment

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.

Centering the Steering System

Shop Talk

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

Centering Procedure

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

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.

POWER-ASSIST STEERINGSYSTEMS

(RECIRCULATING BALL GEARS)

POWER STEERING PUMP

Flow Control and Pressure Relief Valves

TRW/Ross Steering Gear

Operation

Shop Talk

Power steering gear is almost never field-rebuilt in today’s 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.

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.

Equipment for testing hydraulic supply system.

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.

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.

RACK AND PINION STEERING

RACK AND PINION PRINCIPLE

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

ELECTRONICALLY VARIABLE STEERING

LOAD-SENSING POWER STEERING

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

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.

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.