793f brake chassis valve help-rev03
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793F E.H. CHASSIS VALVE
(Electro – Hydraulic Chassis Valve Diagnostic Supplement)
TESTING & ADJUSTING PLUS
TROUBLESHOOTING TIPS
This document is a “Supplement” Guide!
Always refer to the latest information available from
Caterpillar SIS - using SSP serial # prefix, when
troubleshooting any EH Chassis Valve Issues.
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System Pressure Release
Hydraulic System
WARNINGPersonal injury can result from hydraulic oil pressure and hot oil.
Hydraulic oil pressure can remain in the hydraulic system after the
engine has been stopped. Serious injury can be caused if this pressure is
not released before any service is done on the hydraulic system.
Make sure all of the attachments have been lowered; oil is cool before
removing any components or lines. Remove the oil filler cap only when
the engine is stopped, and the filler cap is cool enough to touch withyour bare hand.
Brake
To relieve the pressure from the brake circuit, move the engine start switch to the OFF
position. This will activate a solenoid valve in order to release the hydraulic brake pressure
from the brake accumulators.
Brake Accumulators
WARNING
Hydraulic accumulator contains gas and oil under high pressure.
Improper removal or repair procedures could cause severe injury. To
remove or repair, instructions in the service manual must be followed.
Special equipment is required for testing and charging.
REFER MEDIA NUMBERS: KENR8738 , KENR8579 UNDER THE APPROPRIATE
HEADINGS FOR THE BRAKE SYSTEM ACCUMULATOR (SERVICE / PARKING).
Relieving the pressure in the brake circuit will not release the nitrogen precharge pressure
in the brake accumulators.
TOOLING GROUP REQUIRED: CATERPILLAR ELECTRONIC TECHNICIAN (E.T),COMMUNICATION ADAPTOR GROUP & ADAPTOR CABLE ASSEMBLY.
DIGITAL PRESSURE GROUP – PART # 198 – 4240 AND APPROPRIATE TRANSDUCERS.
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Do you know what you are looking at
and what to look for….?
1. Visual inspection is vital for the correct operation of
the “Full Hydraulic Brake System” on the 793F.
BRAKE E.C.M. SOFTWARE FILE #__________________
Model:_________________ Date:___________
Serial Number:___________Service Meter
Hours:_____________
Visual Inspection
Hose Connections:ComponentDamage
Oil Leaks: Oil Temperature: At least 55 Celsius
Oil Level in Brake Actuation Tank:
Nitrogen Charge Pressure in ALL Brake Accumulators
(1000 psi - +/- 50 psi) @ 21 Degrees Celsius ____________ Psi
Brake Holding Ability Test (1)
Engaged Brake Engine Speed (rpm) Engaged Brake Engine Speed (rpm)
Service Brake Parking Brake
Manual Retarder Secondary Brake
( 1 )The engine speed should reach a minimum of 1400 rpm before there is any machine movement.
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793F BRAKE CONTROL VALVE LAY-OUT
Standard Control Valve # 285-5630
(1) Diverter valve (front service brakes)
(2) Diverter valve (rear service brakes)
# 343-3181 XLP USES # 343-3182
(3) Solenoid valve (brake pump unloader)
# 343-3181 XLP USES # 343-3182
(4) Port for the service brake accumulator
# 262-1955
(5) Plug (orifice for feedback dampening of diverter valve (9)
(6) Port (parking brake pressure sensor)
(7) Filter cartridge
(8) Port for the parking brake accumulators
# 2949048
(9) Diverter valve for the parking and secondary brake
(10) Port for the pressure sensor for the oil supply
# 343-3185
(11) Orifice for the brake charging "OR1"
PS2-Pressure Brake Pump
(12) Valve (brake pump unloader)
# 221-4511
(13) Plug "RAX"
# 223-0016
(14) Port for return to tank “T2”
797F ONLY
The front and rear relays / diverters are serviced as akit. They are matched to open at the same time. AlsoDiverter (1) for the front brakes, when the XLP is beingused, check that the
******VERY IMPORTANT NOTE******
322-3795
pilot assembly is underit. The pilot assembly is what makes the front brake
pressure 80% of the rear (except when ARC is active).
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XLP Brake Control Valve Part
#2839559 uses a different Diverter
Valve for the Front & Rear Service
Brakes.
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(15) Port for the supply oil for the service brakes
(16) Check valve (service brake accumulator)
(17) Port "BCD" -
# 163-1829
(18) Plug (orifice for return oil from diverter valve (2)
NOT USED ON “793F” OR “797F”
(19) Plug (orifice for feedback dampening of diverter valve (2)
(20) Port for the rear service brakes
(21) Plug (orifice for feedback dampening of diverter valve (1)
(22) Port for the front service brakes
(23) Solenoid valve (front automatic retarder control)
(24) Plug (orifice for pilot oil for diverter valve (1)
# 279-6527
(25) Solenoid valve (rear automatic retarder control)
(26) Port for the pilot oil for the hoist
# 279-6527
(27) Port for the oil for the check valve for the TCS
(28) Port for the parking and secondary brakes
FRONT BRAKE COOLING DIVERT
SOLENOID IS NOT USED ON THE
793F OR 797F, BUT IS INSTALLED
CAN BE USED FOR
TROUBLESHOOTING A FAILED CO
ELSEWHERE ON THE VALVE.
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(29) Port for return oil for the service brake valve "T1"
(30) Solenoid valve for the parking and secondary brake
(31) Plug (orifice for pilot oil for diverter valve (9)
(32) Control valve (traction control signal)
# 279-6527
(33) Shuttle valve (rear service brake)
# 171-5704
(34) Shuttle valve (front service brake)
# 294-9050
(35) Port for the return to tank
# 294-9050
(36) Main relief valve
(37) Port for the supply oil
# 320-8118
(38) Solenoid valve for purging the brake accumulator’s
(39) Plug (orifice for purging the parking brake accumulators)
# 294-9049
NOT USED ON 793F or 797F, th
is the same as the “BRAKE
ACCUMULATOR PURGE” Soleno
valve Item # 38
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(40) Port for the pressure sensor for the parking brake accumulator
(41) Pressure reducing valve (pilot oil)
PS 1
(42) Check valve (parking brake accumulator)
# 294-9047
# 163-1829
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(43) Port for the pilot oil from the service brake pedal
(44) Port for the pressure switch for the front brakes(45) Port for the pressure sensor for the service brake accumulator
(46) Port for return oil
PS 3
(47) Plug (orifice for the return oil from diverter valve (2)(48) Plug
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(49) Plug (orifice for purging the service brake accumulator)
# 4 STORB PRESSURE TAP CAN BEPLACED HERE TO READ “SECONDARY
/ PARKING BRAKE” ACCUMULATOR
PRESSURE
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(1) Diverter valve (front service brakes)
(2) Diverter valve (rear service brakes)
(3) Solenoid valve (brake pump unloader)(4) Port for the service brake accumulator
(5) Plug (orifice for feedback dampening of diverter valve (9)
(6) Port (parking brake pressure sensor)
(7) Filter cartridge
(8) Port for the parking brake accumulators
(9) Diverter valve for the parking and secondary brake
(10) Port for the pressure sensor for the supply oil
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(11) Orifice for the brake charging "OR1"
(12) Valve (brake pump unloader)
(14) Port for return to tank "T2"
(15) Port for the supply oil for the service brake
(16) Check valve (service brake accumulator)
(17) Port "BCD" NOT USED ON THE 793F & 797F
(19) Plug (orifice for feedback dampening of diverter valve (2)
(20) Port for the rear service brakes
(21) Plug (orifice for feedback dampening of diverter valve (1)
(22) Port for the front service brakes
(23) Solenoid valve (front automatic retarder control)
(24) Plug (orifice for pilot oil for diverter valve (1)
(25) Solenoid valve (rear automatic retarder control)
(26) Port for the oil for the hoist valve
(27) Port for the oil for the check valve for the TCS
(28) Port for the parking and secondary brakes
(29) Port for return oil for the service brake valve "T1"
(30) Solenoid valve for the parking and secondary brake
(31) Plug (orifice for pilot oil for diverter valve (9)
(32) Control valve (traction control signal)
(33) Shuttle valve (rear service brake)
(34) Shuttle valve (front service brake)
(35) Port for the return to tank
(36) Main relief valve
(37) Port for the supply oil
(38) Solenoid valve for purging the brake accumulators
(39) Plug (orifice for purging the parking brake accumulators)
(40) Port for the pressure sensor for the parking brake accumulator(41) Pressure reducing valve (pilot oil)
(42) Check valve (parking brake accumulator)
(43) Port for the pilot oil from the service brake pedal
(44) Port for the pressure switch for the front brakes
(45) Port for the pressure sensor for the service brake accumulator
(49) Plug (orifice for purging the service brake accumulator)
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LIVE TESTING SPECIFACATIONS
Test Specifications Actual
Value
Accumulator “Cycle Time” After System is Fully Charged,
minimum of 10 cycles30 Seconds
Accumulator Nitrogen Charge Pressure for the Service
Brake & Park Brake
1000 ± 50 psi
at
21° C (70° F)
Cut-In Pressure for the Service Brake 2100 ± 70 psi
Cutout Pressure for the Service Brake 3000 ± 70 psi
Service Brake Pressure at the Slack Adjusters for the StandardWheel Groups (Front & Rear) 675 ± 60 psi
Service Brake Pressure at the Slack Adjusters for the
Extended Life Wheel Groups
FRONT
525 ± 87 psi
REAR
670 - / + 58 psi
Retarder Brake Pressure at the Slack Adjusters for the
Standard Wheel Groups (Front & Rear) 675 ± 116 psi
Retarder Brake Pressure at the Slack Adjusters for the
Extended Life Wheel Groups
FRONT525 ± 116 psi
REAR
670 -/+ 116psi
Park Brake Release Pressure for the Secondary Brake System680 ± 70 psi
Towing Valve Pressure (within 120 seconds of turning motoron)
550 to 650 psi
Main Relief Valve Pressure 3250 ± 50 psi
Pressure for the Pressure Reducing Valve (Pilot Oil)600 -50 + 0 psi
Pilot Pressure for the Service Brake Pedal 718 ± 22 psi
NOTE: When the pump is at Low Idle condition, the cycle time is denoted as the time between Cut-
out and Cut-in pressure. Quicker than 30 seconds on a fully charged system = LEAKAGE
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WHAT IS THE DIFFERERENCE BETWEEN “STANDARD & “XLP”
If the truck is equipped with the Extended Life Power
Train (XLP option), the front brakes are equipped with
three additional brake disc packs and the brake / chassis
Valve includes an additional piston and sleeve. Since the
surface area of the piston is smaller than the surface area
of the service brake relay valve, the relay valve directs a
reduced oil pressure to the brake piston. The reduced
pressure is necessary due to the additional brake disc
packs in the XLP option.
The service brakes on the truck with the additional
retarding will have three more discs and plates. The
standard retarding front brakes are equipped with 10
discs in the front and 15 discs in the rear. Additional
retarding will have 13 discs in the front with the standard
15 in the rear. To develop the proper proportion during
additional retarding, the brake chassis valve will beequipped with an additional sleeve and piston.
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THIS IS ONLY USED ON BRAKE CHASSIS CONTROL VALVE PART # 283-9559
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E.H. CONTROL VALVE PRESSURE CHECKS AND
AJUSTMENTS.
# 3: Brake Filter
#4: Pressure Tap for Main System Pressure & Stand-By
Pressure.
SPECS: Maximum System Pressure = 3250 psi - / + 50 psi
Stand-By System Pressure = 150 psi +/- 150 psi
• To see what the main system pressure is set to, go to
the Brake ECM & override the parameter to OFF for
the “Brake Pump Un-loader Solenoid” & observe
what reading you have on your gauge.
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• Do not run test for any longer than 15 seconds.(Or
you can just un-hook the two pin connector on the
Solenoid)
• To see what your stand –by pressure is set at, let the
system run at low Idle and cycle a few times. Then
read what is on your gauge after system cut –out
takes place.
• The only adjustment that can be made is for Main
System Pressure, corrections are made on the main
system relief valve. Item #2
PLEASE NOTE:
Also when checking accum ulator charging, use a gauge to
check the sensors in ET. The sensors could be causing the
cut in / cut o ut to be off .
A low main relief valve cou ld also cause a stal led charge
where you wou ldn' t cut out.
“ If th is is happening, then p erform the fol lowing tests”
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1. Brake Control Valve
2. Main System Relief
3. Brake Filter
4. Pressure Tap
5. Brake pump Un-loader Solenoid
6. Lock-nut
7. Adjustment Screw
CUT-IN & CUT-OUT PRESSURE
• This pressure is measured at two different places,
first one being on a pressure tap (A) located on the
“Service Brake Accumulator” port and the second
being on the “Parking Brake Accumulator” port
pressure tap (B)
NOTE: E.T. Not required for this test
(1)
Install manual gauge.
(2)
Disconnect 2 pin connector.
(3)
Read manual gauge.
(4)
Re-connect 2 pin connector.
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PRESSURE TAP “A” SERVICE BRAKE
ACCUMULATOR PRESSURE
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• This pressure is not adjustable and is controlled by
the Pump Un-loader Solenoid & Diverter Valve.
• The pressure setting (after a few system cycles) for
the cut-out is (3000 ± 70 psi). The cut-in pressure is
70 percent of the cutout pressure. The cut-in
pressure will be (2100 ± 70 psi).
REMOVE THIS PLUG AND INSTALL
STORB # 4 ADAPTOR & PRESSURE
TAP TO READ “PARKING BRAKE
ACCUMULATOR PRESSURE”
PRESSURE TAP “B”
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6V-3965 Test Fitting & #4 STOB
MALE to #6 STOB FEMALE Adaptor.
Notice the recess area, to allow
installation into the recessed port in
the “Brake Valve”
Modified “PARKER” Test Fitting #4
STOB, notice the recess machined at
one end.
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Leakage
When the pump is at the low idle setting, the pressure
will cycle between the cut-in pressure and the cut-out
pressure. The cycle should occur in Approximately 30seconds @ an operating temperature of Approximately
55 degrees Celsius or better. If this cycle occurs in less
than 30 seconds, there is leakage in the system that must
be corrected. (HOIST LEVER IN HOLD)
1. Start the engine. Allow the brake accumulators to
charge fully. Minimum of 10 cyclesNote: Once the brake accumulators are fully charged, the
cycle between the cut-in and cutout pressure will
increase to 30 seconds.
2. To locate the cause of the excessive leakage, shut
down the engine with the engine shutdown control. Do
not shut down the engine with the ignition key. Theengine shutdown switch is located on the right side of
the machine near the right hand ladder.
3. The pressure in the brake accumulators will decrease
because of leakage in the system and lubrication. If there
is a significant leak, one system will decay more rapidly.
4. Observe the pressure at the accumulators.
Note: Before any components are removed, make sure
that the brake accumulators have been fully discharged.
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If the pressure for the service brake accumulator drops
rapidly, check the following items:Check valve for the service brake
Diverter valve for the service brakes
Solenoid valve for the ARC
Pressure relief valve
Solenoid valve for purging the brake accumulators
Solenoid valve for the brake cooling diverter "BCD"Control valve for the TCS
Hoist control valve
If the pressure for the parking brake accumulator drops
rapidly, check the following:
Diverter valve for the parking brakeSolenoid valve for the parking brake
Solenoid valve for purging the brake accumulators
Control valve for the TCS
Check valve for the parking brake
PLEASE NOTE: Als o on a 793F the primary (Service) should
always bleed off b efore the secondary (Parking ). So thatdoesn 't tel l you th ere is an excessive leak on th e primary
side. If secondary does fal l as fast as or faster than the
pr imary side that would be a clue you have a leak on the
secon dary accum ulators. 797F's have 4 accum ulators and
may have more balanced leak dow n rates.
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(3) Diverter valve (un-loader)(4) Solenoid valve (un-loader)
(5) Plug (orifice for pilot oil diverter valve for un-loader)
If the pressure does not reach the standby pressure for
the brake system, perform the cut-in and the cutout test.
If the pressure at Cut-out (3000 psi) for the brake system
is incorrect, inspect diverter valve (3), solenoid valve (4),
and the orifice of plug (5).
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P.R.V. (PILOT OIL) PRESSURE
• Pilot oil is used for the Hoist Control / Brake
Cooling Valve.
Place gauge @ this pressure tap to
ecord Pilot Oil Pressure. 600 psi
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• Make sure hoist control lever (A) is in the
“HOLD” position.
• If pilot system pressure requires correction,
make adjustment at Item #2- Pilot Relief Valve.
•
Turn adjustment screw clockwise to increasepressure, anti-clockwise to decrease pressure.
Park Brake release pressure: Is controlled by a
Proportional Solenoid Valve & Diverter Valve,
which uses main system pressure. Park brakerelease pressure is checked at pressure tap #2
and the pressure on the gauge must be at 680 ±
70 psi.
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Service Brake Pilot & Application Pressure Check
(1)Pressure tap, Next Page
(2)On this page = Pressure Tap
(2) Control Valve and Mounting, Next Page
(3) Brake accumulator for the service brakes, Next Page
(4) Brake accumulator for the parking brakes, Next Page
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Install at pressure tap item #1, with machine running and
brake system fully charged. Make a few service brake
applications then with the service brake fully depressed,
record your value on the gauge – should be:
718 ± 22 psi
This pressure is also controlled by a Proportional
Solenoid Valve & Diverter Valve, which uses main system
pressure.
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Slack Adjusters (1)
Slack Adjuster Pressure At The Slack Adjuster (2) Pressure At The Wheel (3)
Front Slack Adjuster
Left Front Wheel
Front Slack Adjuster
Right Front Wheel
Rear Slack Adjuster
Left Rear Wheel
Rear Slack AdjusterRight Rear Wheel
( 1 )The pressures should be approximately the same value.
( 2 )Use the pressure tap on the slack adjuster.
( 3 )Measure this pressure at the port that is labeled. "S"
NOTE: Your readings will depend on what Braking System
you are working with “STANDARD” / “XLP”
RESIDUAL SLACK ADJUSTER PRESSURE
Residual oil pressure at the Front & Rear wheels should
be approximately 3.6 to 8.0 psi. Max
NOTE: Low residual pressure indicates a failed slack
adjuster. High residual pressure may indicate a failed
slack adjuster or wrapped brake discs.