SENR5736-03
July 2012
988F and 988F II Wheel Loader
Hydraulic System
988F:
8YG1-209
988F II:
2ZR1-699
Printed in U.S.A.© 2012 Caterpillar, All Rights Reserved
ONE POSITION TWO POSITION THREE POSITION
VENTED
PRESSURIZED
RETURN ABOVE FLUID LEVEL RETURN BELOW FLUID LEVEL
LINES CROSSING LINES JOINING
TWO - WAY THREE - WAY FOUR - WAY
SPRING CONTROL VALVES RESTRICTION LINE RESTRICTION
(FIXED)
PUMP
(2 - SECTION)
SPRING
(ADJUSTABLE)
VARIABILITY LINE RESTRICTION
(VARIABLE)
PRESSURE
COMPENSATION
PUMP
(VARIABLE & PRESSURE
COMPENSATED)
MEASUREMENT
PRESSURE TEMPERATURE FLOW
ROTATING SHAFTS
UNIDIRECTIONAL BIDIRECTIONAL
PUSH - PULL LEVER PEDALGENERAL MANUAL PUSH BUTTON SPRING
FIXED
DISPLACEMENT
VARIABLE DISPLACEMENT
NON-COMPENSATED
UNIDIRECTIONAL
BIDIRECTIONAL
VALVE ENVELOPES VALVE PORTS
FLUID CONDITIONERPUMP OR MOTOR
FLUID POWER SYMBOLS
UNIDIRECTIONAL
BIDIRECTIONAL
RELEASED PRESSURE
EXTERNAL RETURN INTERNAL RETURN
REMOTE SUPPLY PRESSURE
SIMPLIFIED
HYDRAULIC PUMPS
ACCUMULATORS
SPRING LOADED GAS CHARGED
SOLENOID
OR MANUAL
SOLENOID
& PILOT
SOLENOID &
PILOT OR MANUAL
SOLENOID SERVO THERMAL DETENT
HYDRAULIC & PNEUMATIC CYLINDERS
DOUBLE ACTINGSINGLE ACTING
BASIC
SYMBOL
SPRING
LOADED
CHECK VALVES
2 POSITION
INFINITE
POSITIONING
FLOW IN ONE
DIRECTION
FLOW IN
EITHER
DIRECTION
3 POSITION
CROSS
FLOW
PARALLEL
FLOW
INTERNAL PASSAGEWAYS
NORMAL POSITION
AB
PT
AB
PT
SHIFTED POSITION INFINITE POSITION
CONTROL VALVES
ATTACHMENT
MANUAL SHUTOFF
SHUTTLE PILOT
CONTROLLED
MAIN AUX
LINE RESTRICTION
(VARIABLE & PRESSURE
COMPENSATED)
MANUAL CONTROL SYMBOLS
HYDRAULIC MOTORS
FLUID STORAGE RESERVOIRS
CROSSING & JOINING LINES
VALVES
PILOT CONTROL SYMBOLS
COMBINATION CONTROLS
BASIC COMPONENT SYMBOLS
ENERGY TRIANGLES
HYDRAULIC PNEUMATIC
INTERNAL
SUPPLY PRESSURE
COMPLETE
FIXED
DISPLACEMENT
VARIABLE DISPLACEMENT
NON-COMPENSATED
HYDRAULIC SYMBOLS (ELECTRICAL)
ELECTRICAL SYMBOLS TABLE
325-AG135 PK-14
HARNESS IDENTIFICATION CODE THIS EXAMPLE
INDICATES WIRE 135 IN HARNESS “AG”
325-PK-14
WIRE GAUGE
WIRE COLOR
CIRCUIT NUMBER
IDENTIFICATION
WIRE NUMBER IDENTIFICATION CODES
CURRENT STANDARD
PREVIOUS STANDARD
ELECTRICAL SCHEMATIC EXAMPLE HYDRAULIC SCHEMATIC EXAMPLE
325-PK
WIRE COLOR
CIRCUIT NUMBER
IDENTIFICATION
B
WIRE
WIRE
(EXAMPLE VALVE)
CURRENT STANDARD
TRANSDUCER
(FLUID)
M
ELECTRIC MOTORTRANSDUCER
(GAS / AIR)
G
GENERATOR
PRESSURE SWITCH ELECTRICAL WIREPRESSURE SWITCH
(ADJUSTABLE)
TEMPERATURE
SWITCH
PRESSURE
SWITCH
TEMPERATURE
SWITCH
LEVEL
SWITCH
FLOW
SWITCH
ELECTRICAL SYMBOLS (ELECTRICAL)
A
CIRCUIT NUMBER
IDENTIFICATION
WIRE
COLOR
WIRE GAUGE
T
SENR5736-03
20 Page, (Dimensions: 39 inches x 24 inches)
13
32
18
42
27
23 34
30
45
36
6
27
26
38
7
21 2 53 5
24
10
20
8
4
21
16
12
19
925
26
22
39 33
41
40
48
17
28
47
43
35
51
50
52
37
49
46
14
44
29
31
1
11
E
D
B
G
C
A
F
A
B
VIEW A
VIEW B
PILOT VALVE
SERVICE BRAKE
MACHINE COMPONENT AND TAP LOCATIONS
Tap
Number
Description
Schematic
Location
A Steering System D-8 , D-9
B Brake System C-6
C Pilot Pressure B-6
D Implement Relief Pressure C-3
E Tilt Head End Pressure D-2
F Tilt Rod End Pressure D-2
G Accumulator Pressure C-5
Tap Location
Pressure and Sampling
Note A: Refer to the Parts Manual for your specific machine.
Description
Machine
Location
Schematic
Location
988F 988F II
Accumulator (Ride Control Att.) NOT USED 6E-6400 1 D-1
Accumulator Gp - Brake Oil 100-6909 100-6909 2 C-6
Cylinder Gp - Auxiliary NOTE A NOTE A 3 D-2
Cylinder Gp - Lift 9T-8257 9T-8257 4 D-1
Cylinder Gp - Steering 9J-8165 9J-8165 5 D-8 , D-9
Cylinder Gp - Tilt (High Lift) 4T-6792 4T-6792
Cylinder Gp - Tilt (Logger) 3G-2976 3G-2976
Cylinder Gp - Tilt (Standard) 9J-3632 9J-3632
Filter Gp - Fan Drive Oil 4T-4284 4T-4284 7 D-6
Filter Gp - Main Oil NOTE A NOTE A 8 B-6
Fi
lter Gp - Pilot System Oil 6P-4603 6P-4603 9 B-6
Hydraulic Tank 9T-4971 9T-4971 10 B-6
Junction Block 2V-7777 2V-7777 11 B-6
Motor Gp - Fan Drive Motor (High Ambient) - 110-6351
Motor Gp - Fan Drive Motor (Standard) 6E-1141 6E-1141
Oil Cooler 4P-4710 4P-4710 13 D-7
Orifice 4.00E-110 7I-3032
- 127-5801
Parking Brake - - 15 D-4
Pump Gp - Fan Drive Pump (High Ambient) 6E-6425 6E-6425
Pump Gp - Fan Drive Pump (Standard) 6E-1229 6E-1229
Pump
Gp - Hand Metering (Steering) 6E-2726 6E-2726 17 B-9
Pump Gp - Implement (Logger) 6E-5853 6E-5853
Pump Gp - Implement (Standard) 6E-3718 109-3420
Pump Gp - Steering (Brake And Pilot) 6E-3719 109-3421 19 B-7
Pump Gp - Supplimental Steering 3G-6856 3G-6856 20 B-9
Service Brakes - - 21 C-5
Switch As - Low Brake Oil Pressure Switch 3E-6452 174-4312 22 D-6
Switch As - Parking Brake 3E-6452 171-7085 23 C-4
Switch As - Supplemental Steeri
ng Flow 9X-0008 9X-0008 24 B-6
Switch As - Transmission Neutralizer 4E-8950 4E-8950 25 C-5
Valve Gp - Brake Control 9J-4080 9J-4080 26 C-5
Valve Gp - Brake Oil Accumulator Charging 9J-4693 9J-4693 27 C-6
Valve Gp - Check 104-7108 104-7108 28 B-6
Valve Gp - Check 9T-4543 9T-4543 29 B-7
Valve Gp - Check 104-7108 104-7108 30 B-8
Valve GP - Diverter (Ride Control Att.) NOT USED 124-5752 31 C-1
Valve Gp - Fan Drive Make-Up (High Ambient) NOT
USED 110-5270
Valve Gp - Fan Drive Make-Up (Standard) 105-2470 105-2470
Valve Gp - Fluid Sample 8C-3446 8C-3446 33 B-6
Valve Gp - Hydraulic Tank Relief 9T-0818 9T-0818 34 B-6
Valve Gp - Left Steering Neutralizer
Stick Steer 9T-7426 9T-7426 35 C-8
Wheel Steer 8J-1553 8J-1553 35 C-9
Valve Gp - Lift Cylinder Head End Check 9T-3096 9T-3096 36 B-1
Valve Gp - Lift Cylinder Rod End Check 9T-3096 9T-3096 37 C-1
Valve Gp - Oil Cooler Bypass
6E-1129 6E-1129 38 D-7
Valve Gp - Parking Brake Control 100-8941 100-8941 39 D-5
Valve Gp - Pilot (Tilt and Lift) 108-6262 111-1528 40 D-3
Valve Gp - Pilot (Tilt, Lift and Aux) 108-6263 111-1529 41 D-3
Valve Gp - Pilot System Relief 6E-6178 6E-6178 42 B-6
Valve Gp - Right Steering Neutralizer
Stick Steer 9T-7426 9T-7426 43 C-7
Wheel Steer 8J-1553 8J-1553 43 C-9
Valve Gp - Selector 6E-5566 6E-5566 44 B-8
Valve Gp - Selector 6E-5566 6E-5566
45 B-5
Valve Gp - Steering Control
Stick Steer 6E-4031 128-5347 46 D-8
Wheel Steer 8J-2318 8J-2318 46 D-9
Valve Gp - Steering Dual Check 6E-3723 6E-3723 47 C-7
Valve Gp - Steering Pilot Control 6E-3182 6E-3182 48 C-8
Valve Gp - Supplimental Steering Diverter 8J-6099 8J-6099 49 A-9
Valve Gp -Control (Tilt and Lift) 9T-1484 9T-1484 50 C-2
Valve Gp -Control (Tilt, Lift and Aux) 9T-1483 9T-1483 51 C-2
Valve Gp -Main Relief (Logger) 3G-3
460 3G-3460
Valve Gp -Main Relief (Standard) 6E-2920 6E-2920
Valve Gp - Relief NOT USED 118-4297 53 D-7
D-6
Component Location
6D-2
12 D-6
52 C-3
Part Number
14 D-7
18 B-4
32 D-6
16
SENR5736-03
20 Page, (Dimensions: 39 inches x 24 inches)
Components are shown installed on a fully operable machine with the key and engine off, transmission shifter
in neutral and with parking brake set.
Refer to the appropriate Service Manual for Troubleshooting, Specifications and Systems Operations.
SCHEMATIC PART NUMBER: 128-5712, CHANGE: 00, VERSION: -
SCHEMATIC PART NUMBER: 6E-5381, CHANGE: 00, VERSION: -
MEDIA NUMBER: SENR5736-03
THIS SCHEMATIC IS FOR THE 988F AND 988F II WHEEL LOADER HYDRAULIC SYSTEM
A
B
C
D
E
12345678
9
A
B
C
D
E
123456789
LINE PATTERNS
Drain / Return Lines
Component Group
Pilot / Load Sensing Pressure
Pressure Line
Attachment
Air Line
CALLOUTS
Taps (Pressure, Sampling, Sensor - by letter)
YY
HYDRAULIC CIRCUIT COLOR DESCRIPTIONS
PILOT CIRCUIT
IMPLEMENTS PUMPS
SUPPLIMENTAL STEERING PUMP
TILT CYLINDERS
STEERING CIRCUIT
SUPPLY LINE
PARKING AND SERVICE BRAKE
DRAIN / RETURN LINE
LIFT CYLINDER
AUX CYLINDERS
STICK STEERWHEEL STEER
Parking and Service Brake
STEER
IMPL CASE DRAIN
LIFT CYL PRESSURE
IMP PILOT VALVE RETURN
IMPL PILOT SUPPLY
IMPL RETURN
IMPL PUMP SUPPLY
SERVICE
BRAKE
PRESSURE
PARKING
BRAKE
PRESSURE
RAISE/OPEN
RACK BACK
RAISE
VENT
LIFTAUX
P
P
T
R.E.
H.E.
T
DUMP
DUMP
RACK BACK
LOWER
TILT
LOWER
RAISE
T
T
R.E
H.E.
P
PP
P
H.E.
R.E
T
RAISE/OPEN
LOWER/CLOSE
T
LOWER/CLOSE
LEFT RIGHT
T
ACU
R.E.
H.E.
(38) VALVE GP
OIL COOLER BYPASS
6E-1129
(53) VALVE GP
RELIEF
118-4297
(22) SWITCH AS
LOW BRAKE OIL PRESSURE
174-4312 (988F II)
3E-6452 (988F)
(7) FILTER GP
FAN DRIVE OIL
4T-4284
(2) ACCUMULATOR GP
BRAKE OIL
100-6909
(14) ORIFICE
7I-3032, 127-5801(For 988F II Only)
4E-0110
(16) PUMP GP
FAN DRIVE PUMP
(STANDARD) - 6E1229
(HIGH AMBIENT) - 6E-6425
(12) MOTOR GP
FAN DRIVE MOTOR
(STANDARD) - 6E1141
(HIGH AMBIENT) - 110-6351
(32) VALVE GP
FAN DRIVE MAKE-UP
(STANDARD) - 105-2470
(HIGH AMBIENT) - 110-5270
(27) VALVE GP
BRAKE OIL
ACCUMULATOR CHARGING
9J-4693
(39) VALVE GP
PARKING BRAKE CONTROL
100-8941
(40) VALVE GP
PILOT (TILT AND LIFT)
111-1528 (998F II)
108-6262 (988F)
(31) VALVE GP
DIVERTER
(RIDE CONTROL ATT.)
124-5752
(37) VALVE GP
LIFT CYLINDER
ROD END CHECK
9T-3096
(36) VALVE GP
LIFT CYLINDER
HEAD END CHECK
9T-3096
(1) ACCUMULATOR
(RIDE CONTROL ATT.)
6E-6400
(3) CYLINDER GP
AUXILIARY
(4) CYLINDER GP
LIFT
9T-8257
(6) CYLINDER GP
TILT
(STANDARD) - 9J-3632
(LOGGER) - 3G-2976
(HIGH LIFT) - 4T-6792
(41) VALVE GP
PILOT (TILT, LIFT AND AUX)
111-1529 (988F II)
108-6263 (988F)
(51) VALVE GP
CONTROL (TILT, LIFT AND AUX)
9T-1483
(52) VALVE GP
MAIN RELIIEF
(STANDARD) - 6E-2920
(LOGGER) - 3G-3460
(50) VALVE GP
CONTROL (TILT AND LIFT)
9T-1484
(18) PUMP GP
IMPLEMENT
(STANDARD) - 109-3420(988F II) , 6E-3718(988F)
(LOGGER) - 6E-5853
988F II ONLY
(26) VALVE GP
BRAKE CONTROL
9J-4080
(9) FILTER GP
PILOT SYSTEM OIL
6P-4603
(28) VALVE GP
CHECK
104-7108
(30) VALVE GP
CHECK
104-7108
(29) VALVE GP
CHECK
9T-4543
(45) VALVE GP
SELECTOR
6E-5566
(42) VALVE GP
PILOT SYSTEM RELIEF
6E-6178
(33) VALVE GP
FLUID SAMPLE
8C-3446
(34) VALVE GP
HYDRAULIC TANK RELIEF
9T-0818
(19) PUMP GP
STEERING (BRAKE AND PILOT)
109-3421 (988F II)
6E-3719 (988F)
(20) PUMP GP
SUPPLIMENTAL STEERING
3G-6856
(49) PUMP GP
SUPPLIMENTAL STEERING DIVERTER
8J-6099
(24) SWITCH AS
SUPPLIMENTAL STEERING FLOW
9X-0008
(10) HYDRAULIC TANK
9T-4971
(11) JUNCTION BLOCK
2V-7777
(8) FILTER GP
MAIN OIL
(23) SWITCH AS
PARKING BRAKE
171-7085 (988F II)
3E-6452 (988F)
(21) SERVICE BRAKES
(21) SERVICE BRAKES
(25) SWITCH AS
TRANSMISSION
NEUTRALIZER
4E-8950
(15) PARKING BRAKE
(13) OIL COOLER
4P-4710
(5) CYLINDER GP
STEERING
9J-8165
(46) VALVE GP
STEERING CONTROL
8J-2318
(35) VALVE GP
LEFT STEERING
NEUTRALIZER
8J-1553
(17) PUMP GP
HAND METERING
(STEERING)
6E-2726
(35) VALVE GP
LEFT STEERING
NEUTRALIZER
9T-7426
(48) VALVE GP
STEERING PILOT
CONTROL
6E-3182
(47) VALVE GP
STEERING DUAL
CHECK
6E-3723
(43) VALVE GP
RIGHT STEERING
NEUTRALIZER
9T-7426
(43) VALVE GP
RIGHT STEERING
NEUTRALIZER
8J-1553
(44) VALVE GP
SELECTOR
6E-5566
(46) VALVE GP
STEERING CONTROL
128-5347 (988F II)
6E-4031 (988F)
(5) CYLINDER GP
STEERING
9J-8165
F
E
B
C
RIGHT
TURN
STEERING
CYLINDERS
A
D
G
A
RIGHT
TURN
STEERING
CYLINDERS
LEFT
RIGHT
A
B
B
A
C
D
A
B
C
E
E
CD
TO LIGHT
ON DASH
D
