Service Training MALAGA
777D Off Highway Truck
STEERING SYSTEM
HOLD
ELECTRONIC CONTROL MODULE STEERING HYDRAULIC TANK HAND METERING UNIT (HMU)
CROSSOVER RELIEF VALVES
OIL FILTER MAGNETIC SWITCH
MAIN RELIEF CHECK VALVE
SECONDARY STEERING PUMP
CHECK VALVE
FLOW SWITCH ACCUMULATOR STEERING PUMP FLOW CONTROL VALVE STEERING CYLINDERS
VII STEERING.
1. 2. 3. 4. Components Layout Operation Maintenance Testing & Adjusting
777D Off Highway Truck
CHAPTER : STEERING
TYPICAL OFF-HIGHWAY TRUCK STEERING COMPONENT LOCATIONS
SECONDARY STEERING PUMP ELECTRIC MOTOR HYDRAULIC TANK FLOW CONTROL VALVE STEERING CYLINDERS STEERING PUMP
HMU
STEERING ECM OIL FILTER ACUMULATOR
HOIST PUMP
HMU
CROSSOVER RELIEF VALVES
STEERING PUMP
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VI-1
Page: VI-2
STEERING SYSTEM
HOLD
HAND METERING UNIT (HMU) ELECTRONIC CONTROL MODULE
CROSSOVER RELIEF VALVES
STEERING HYDRAULIC TANK
OIL FILTER MAGNETIC SWITCH
CHAPTER : STEERING
MAIN RELIEF CHECK VALVE
777D Off Highway Truck
SECONDARY STEERING PUMP FLOW SWITCH
CHECK VALVE
ACCUMULATOR STEERING PUMP FLOW CONTROL VALVE STEERING CYLINDERS
Page: VI-3
STEERING SYSTEM
RIGHT TURN
HAND METERING UNIT (HMU) ELECTRONIC CONTROL MODULE
CROSSOVER RELIEF VALVES
STEERING HYDRAULIC TANK
OIL FILTER
CHAPTER : STEERING
MAGNETIC SWITCH
777D Off Highway Truck
SECONDARY STEERING PUMP
STEERING PUMP
ACCUMULATOR FLOW CONTROL VALVE STEERING CYLINDERS
777D Off Highway Truck
CHAPTER : STEERING
STEERING FLOW CONTROL VALVE
TO HMU
MAIN RELIEF VALVE FROM HMU
CHECK VALVE
FLOW CONTROL ORIFICE
TO TANK CHECK VALVE FROM SECONDARY STEERING PUMP FROM PUMP
CHECK VALVE
SIGNAL TO SECONDARY STEERING
FLOW SWITCH CLOSED
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VI-4
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HAND METERING UNIT HOLD
INPUT SHAFT
BALL IN HELICAL GROOVE
STATIONARY GEAR
COMMUTATOR
CHAPTER : STEERING
777D Off Highway Truck
TORSION BAR VALVE SPOOL TO TO TO TANK CYLINDER CYLINDER ROTATING GEAR DRIVE LINK
FROM PUMP
Page:
HAND METERING UNIT
LEFT TURN
VI-6
COMMUTATOR STATIONARY GEAR BALL INPUT SHAFT CHAPTER : STEERING
777D Off Highway Truck
TORSION BAR TO TANK FROM TO PUMP CYLINDER ROTATING GEAR DRIVE LINK
VALVE SPOOL
FROM CYLINDER
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HAND METERING UNIT
RIGHT TURN STATIONARY GEAR COMMUTATOR INPUT SHAFT BALL
CHAPTER : STEERING
777D Off Highway Truck
TORSION BAR FROM CYLINDER TO TANK TO CYLINDER FROM PUMP
VALVE SPOOL
ROTATING GEAR
DRIVE LINK
777D Off Highway Truck
CHAPTER : STEERING
CROSSOVER RELIEF SYSTEM
EXTERNAL IMPACT
CROSSOVER RELIEF VALVES
HAND METERING UNIT
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VI-8
777D Off Highway Truck
CHAPTER : STEERING
LAB EXERCISES
LAB A: STEERING SYSTEM COMPONENT IDENTIFICATION Directions: Place the correct letter or number next to the component and briefly describe the function of each. Steering System Components Flow Control Valve and Flow Switch
Hand Metering Unit
Oil Filter
Steering Pump
Secondary Steering Electronic Control Module
Secondary Steering Magnetic Switch
Secondary Steering Pump
Crossover Relief Valves
Accumulator (777D truck only)
Steering Hydraulic Tank
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VI-9
777D Off Highway Truck
CHAPTER : STEERING
LAB EXERCISES
LAB B: STEERING SYSTEM TESTING Machine Model __________________________ Date_______________________________ Serial Number ___________________________ Technician___________________________
VISUAL CHECKS: Oil level _______________ Oil Viscosity _______________ Air/Water in Oil ?_______ Suction Screen Debris ? _______ Oil leaks ? ______________ Oil Filter Examination ______
PRESSURE TESTS TEST Full Cycle Time at High Idle Main Relief Valve Pressure (Left Turn) at High Idle Main Relief Valve Pressure (Right Turn) at High Idle Crossover Relief Valve (Left Turn) at Low Idle Crossover Relief Valve (Right Turn) at Low Idle Accumulator Charge Pressure SPECIFICATIONS ACTUAL
SECONDARY STEERING SYSTEM TEST The truck should be on flat level ground with the parking brake engaged. Turn the ignition switch ON (engine off) and actuate the secondary pump automatic/manual switch to the MANUAL position. Then, attempt to turn the steering wheel. You should be able to hear the secondary pump motor run and the front wheels of the truck should turn.
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VI-10
777D Off Highway Truck
CHAPTER : STEERING
LAB EXERCISES
LAB C: TRACING STEERING SYSTEM OIL FLOW I. Directions: Have each student trace the flow of oil during the conditions listed below using different colored pencils to show each path: Steering system when the steering wheel is stationary Steering system when the steering wheel is turned to the right or left
HAND METERING UNIT (HMU) CROSSOVER RELIEF VALVES
STEERING HYDRAULIC TANK OIL FILTER
STEERING CYLINDERS SECONDARY STEERING PUMP
ACCUMULATOR FLOW CONTROL VALVE
STEERING PUMP
HAND METERING UNIT (HMU)
CROSSOVER RELIEF VALVES
STEERING HYDRAULIC TANK OIL FILTER
STEERING CYLINDERS SECONDARY STEERING PUMP
ACCUMULATOR FLOW CONTROL VALVE
STEERING PUMP
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VI-11
777D Off Highway Truck
CHAPTER : STEERING
LAB EXERCISES
LAB C: TRACING STEERING SYSTEM OIL FLOW (CONT.) II. Directions: Have each student trace the flow of oil during the conditions listed below using different colored pencils to show each path: Flow control valve under normal conditions Flow control valve when the secondary steering system is in operation Flow control valve when system pressure exceeds the setting of the main relief valve.
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VI-12
777D Off Highway Truck
CHAPTER : STEERING
LAB EXERCISES
LAB D: STEERING SYSTEM TROUBLESHOOTING Machine Model __________________________ Date_______________________________ Serial Number ___________________________ Technician___________________________
VISUAL CHECKS: Oil level _______________ Oil Viscosity _______________ Air/Water in Oil ?_______ Suction Screen Debris ? _______ Oil leaks ? ______________ Oil Filter Examination ______
PRESSURE TESTS TEST Full Cycle Time at High Idle Main Relief Valve Pressure (Left Turn) at High Idle Main Relief Valve Pressure (Right Turn) at High Idle Crossover Relief Valve (Left Turn) at Low Idle Crossover Relief Valve (Right Turn) at Low Idle Accumulator Charge Pressure SPECIFICATIONS ACTUAL
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VI-13
777D Off Highway Truck
CHAPTER : STEERING
POST TEST
Off-Highway Trucks Steering System Posttest I. Directions: Match the component to the correct statement below. 1. Crossover Relief Valves 2. Oil Filter 3. Flow Control Valve 4. Hand Metering Unit Dampens pressure surges in the steering system. Contains an oil filter. Contains a check valve to prevent pressure surges from the steering cylinders from returning to the HMU when a turn is in progress. Meters and redirects oil to the steering cylinders as the steering wheel is turned. Equalizes the pressure in both steering cylinders if the pressure in one cylinder exceeds the relief valve setting. Utilizes a bypass valve to protect the steering system during cold oil start-up. Is energized by a magnetic switch. Indicates to the electronic control module a loss of oil flow. II. Directions: Indicate whether the statement is True or False by circling the corresponding letter. 1. The secondary steering motor is tested every time the ignition switch is turned to the ON position. (T) or F 2. The crossover relief valve pressure setting is higher than the setting of the main steering relief valve (in the flow control valve). (T) or F 3. The crossover relief valves should be checked at low idle and are adjustable. T or (F) 4. When the steering wheel is stationary, steering oil circulates through the Hand Metering Unit (HMU), back to the steering hydraulic tank, and oil flow is blocked to and from the steering cylinders. (T) or F 5. All truck models are equipped with an accumulator that uses a nitrogen gas charge to cushion the steering system from pressure surges. T or (F) Page: VI-14 5. Steering Hydraulic Tank 6. Secondary Steering Pump 7. Flow Switch 8. Accumulator
777D Off Highway Truck
CHAPTER : STEERING
POST TEST
III. Directions: Match the components with the associated letter. STEERING SYSTEM
A I
E D
H K G
Flow Control Valve Oil Filter Crossover Relief Valves Secondary Steering Pump Steering Hydraulic Tank Automatic/Manual Panel Switch
Hand Metering Unit Steering Pump Steering Cylinders Accumulator Magnetic Switch Electronic Control Module
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VI-15
777D Off Highway Truck
CHAPTER : STEERING
POST TEST
IV. Directions: Match the components and ports with the associated letter. FLOW CONTROL VALVE Flow Switch To Hand Metering Unit Relief Valve Secondary Steering Pump Inlet From Hand Metering Unit Steering Pump Inlet Flow Control Orifice To Steering Hydraulic Tank
E G F
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