Caterpillar Brake Systems Troubleshooting PDF

GLOBAL DEALER LEARNING Brake Systems Troubleshooting Hydraulic Brake Systems MODULE 1 - TEXT REFERENCE SERVxxxx © 2024 Caterpillar. All Rights Reserved. CAT, CATERPILLAR, LET’S DO THE WORK, their respective logos, “Caterpillar Corporate Yellow”, the “Power Edge” and Cat “Modern Hex” trade dress...

GLOBAL DEALER LEARNING Brake Systems Troubleshooting Hydraulic Brake Systems MODULE 1 - TEXT REFERENCE SERVxxxx © 2024 Caterpillar. All Rights Reserved. CAT, CATERPILLAR, LET’S DO THE WORK, their respective logos, “Caterpillar Corporate Yellow”, the “Power Edge” and Cat “Modern Hex” trade dress as well as corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -2- Module 1 - Hydraulic Brake Systems TABLE OF CONTENTS SAFETY BRIEFING 4 PURPOSE 5 REASON 6 ASSESSMENT CRITERIA 7 LEARNING OUTCOMES 8 LEARNING OUTCOMES (CONT.) 9 HYDRAULIC BRAKE SYSTEMS INTRODUCTION 10 HYDRAULIC BRAKE SYSTEMS OVERVIEW 11 MASTER CYLINDER (CWL) 13 MASTER CYLINDER (BHL) 14 BOOSTED MASTER CYLINDER REVIEW 17 BOOSTED MASTER CYLINDER OPERATION (BHL) 18 BOOSTED MASTER CYLINDER OPERATION (CWL) - BRAKES RELEASED 19 BOOSTED MASTER CYLINDER OPERATION (CWL) - BRAKES ENGAGED 20 BOOSTED MASTER CYLINDER OPERATION (TH) - BRAKES RELEASED 22 BOOSTED MASTER CYLINDER OPERATION (TH) - BRAKES ENGAGED 24 HYDRAULIC ACCUMULATOR BRAKE SYSTEM REVIEW 26 BRAKE CHARGING VALVE (CUT-IN) 27 BRAKE CHARGING VALVE (CUT-OUT) 29 ACCUMULATOR CHARGING (LWL) 31 COMBINATION VALVE (MG) 32 COMBINATION VALVE (MWL) 34 SYSTEMS TESTING AND ADJUSTING OVERVIEW 35 OPERATIONAL CHECKS: BRAKE HOLDING TESTS 36 BRAKE ACCUMULATOR CHECK: HYDRAULIC ACCUMULATOR BRAKE SYSTEMS 38 ACCUMULATOR PRESSURE 39 SERVICE BRAKE PRESSURE TEST: MASTER CYLINDER BRAKE SYSTEM 40 SERVICE BRAKE PRESSURE: HYDRAULIC ACCUMULATOR BRAKE SYSTEM 41 ACCUMULATOR PRESSURE (CUT-IN/CUT-OUT) TEST 42 ACCUMULATOR BRAKE PRESSURE ADJUSTMENT 43 PARKING BRAKE PRESSURE 44 Caterpillar: Confidential Yellow SERVxxxx - 12/24 -3- Module 1 - Hydraulic Brake Systems SYSTEM TROUBLESHOOTING OVERVIEW 45 CATERPILLAR 7-STEP DIAGNOSTIC PROCESS 46 INITIAL INSPECTION 48 SYMPTOM TROUBLESHOOTING 50 MASTER CYLINDER 51 SERVICE BRAKE ASSEMBLY 52 BRAKE CHARGING VALVE 53 BRAKE ACCUMULATORS 54 SERVICE BRAKE CONTROL VALVE 55 PARKING BRAKE CONTROL VALVE 56 PARKING BRAKE ASSEMBLY 57 PURPOSE REVIEW 58 REASON REVIEW 59 ASSESSMENT CRITERIA REVIEW 60 LEARNING OUTCOMES REVIEW 61 LEARNING OUTCOMES REVIEW (CONT.) 62 MODULE CONCLUSION 63 Caterpillar: Confidential Yellow SERVxxxx - 12/24 -4- Module 1 - Hydraulic Brake Systems SAFETY BRIEFING Emergency Phone Numbers First Aid Responders Location of Exits Location of Fire Extinguisher Room Alerts or Hazards Designated Location for Evacuation Storm Shelter Hazardous Material Safely Home. Everyone. Every Day.™ 4 SAFETY BRIEFING Before beginning this module, the following topics will be reviewed: Emergency Phone Numbers First Aid Responders Location of Exits Location of Fire Extinguisher Room Alerts or Hazards Designated Location for Evacuation Storm Shelter Hazardous Material Safely Home. Everyone. Every Day.™ NOTE: Any system or component specifications stated in this training module are used only for training purposes. Components and specifications may change as the product evolves. Always refer to Caterpillar Service information to obtain the most current specifications when servicing Cat products. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -5- Module 1 - Hydraulic Brake Systems PURPOSE This module covers hydraulic brake system components, operation, testing, and troubleshooting procedures for machines equipped with hydraulic brake systems. 5 PURPOSE Explain the purpose of this This module covers hydraulic brake system components, operation, testing, and module. troubleshooting procedures for machines equipped with hydraulic brake systems. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -6- Module 1 - Hydraulic Brake Systems REASON Successful completion validates the knowledge, skills, and behaviors that are required to properly diagnose and repair hydraulic brake systems used in Cat® machines. 6 REASON Explain the reason for this Successful completion validates the knowledge, skills, and behaviors that are module. required to properly diagnose and repair hydraulic brake systems used in Cat machines. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -7- Module 1 - Hydraulic Brake Systems ASSESSMENT CRITERIA Knowledge Assessment Closed book Minimum passing score of 80% Skills Assessment Competent/Not Yet Competent or Instructor Observation Test procedures are performed correctly 7 ASSESSMENT CRITERIA Explain the assessment criteria After the completion of this module, the participant must complete a knowledge for this module. assessment with a minimum passing score of 80%. The instructor will determine whether the participant is competent or not yet competent to perform the hydraulic brake tests. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -8- Module 1 - Hydraulic Brake Systems LEARNING OUTCOMES After completing this Hydraulic Brake Systems module of the Brake Systems Troubleshooting course you should be able to: Identify hydraulic brake systems components. Explain hydraulic brake systems operation. Describe the different applications of hydraulic brake systems. Describe hydraulic brake systems testing and adjusting procedures. Describe hydraulic brake systems troubleshooting procedures. Perform hydraulic brake systems testing and adjusting procedures. 8 LEARNING OUTCOMES Explain the learning outcomes of After the completion of this module, the participant will be able to: this module. Identify hydraulic brake systems components. Explain hydraulic brake systems operation. Describe the different applications of hydraulic brake systems. Describe hydraulic brake systems testing and adjusting procedures. Describe hydraulic brake systems troubleshooting procedures. Perform hydraulic brake systems testing and adjusting procedures. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -9- Module 1 - Hydraulic Brake Systems LEARNING OUTCOMES (CONT.) After completing this Hydraulic Brake Systems module of the Brake Systems Troubleshooting course you should be able to: Perform hydraulic brake systems troubleshooting procedures. 9 LEARNING OUTCOMES (CONT.) Explain the learning outcomes of After the completion of this module, the participant will be able to: this module. Perform hydraulic brake systems troubleshooting procedures. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -10- Module 1 - Hydraulic Brake Systems HYDRAULIC BRAKE SYSTEMS INTRODUCTION 10 HYDRAULIC BRAKE SYSTEMS INTRODUCTION Introduction to hydraulic brake This module is an introduction to hydraulic brake systems. systems. NOTE: The Caterpillar 7-Step Diagnostic Process was introduced in the basic service curriculum and will be referred to throughout the advanced courses to promote an organized method of problem solving. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -11- Module 1 - Hydraulic Brake Systems HYDRAULIC BRAKE SYSTEMS OVERVIEW 2 4 3 1 Hydraulic Master Cylinder Hydraulic Boosted Hydraulic Brake Master Cylinder Accumulator 11 1. Master cylinder 3. Hydraulic boosted master cylinder 2. Oil reservoir 4. Hydraulic brake accumulator HYDRAULIC BRAKE SYSTEMS OVERVIEW Give an overview of hydraulic This section covers the system operation of various hydraulic brake systems that brake systems. are currently used or have been used on Cat Machines. Hydraulic brake systems discussed include: Master Cylinder With a master cylinder (1), the brake pedal is mechanically connected to the master cylinder, which uses oil from a reservoir (2) to apply the brakes. No external hydraulic source is required. Hydraulic Boosted Master Cylinder With a hydraulic boosted master cylinder (3), an external hydraulic oil source is used to reduce the amount of pedal effort required by the operator. This oil is supplied from another hydraulic system such as the pilot system or hydraulic fan system. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -12- Module 1 - Hydraulic Brake Systems Hydraulic Accumulator A hydraulic pump is used to supply oil to the braking system, via one or more hydraulic brake accumulators (4). The accumulators store supply oil to make sure oil under pressure is available when the services brakes are applied. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -13- Module 1 - Hydraulic Brake Systems MASTER CYLINDER (CWL) 2 3 1 4 906-908 Compact Wheel Loader 13 1. Master cylinder 3. Service brake pedal 2. Brake oil reservoir 4. Brake caliper MASTER CYLINDER (CWL) Identify the brake hydraulic This example shows the brake hydraulic system on a Compact Wheel system on a Compact Wheel Loader (CWL), which is equipped with a master cylinder (1) that is not Loader (CWL) equipped with hydraulically boosted. a master cylinder that is not hydraulically boosted. The operator’s pedal force is transferred to the master cylinder where the force is multiplied directly into the brake system. The supply oil for the brake hydraulic system is contained in the brake reservoir (2). The service brake pedal (3) controls the brake master cylinder, which sends oil under pressure to the brake piston in the brake caliper (4). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -14- Module 1 - Hydraulic Brake Systems MASTER CYLINDER (BHL) 3 2 1 14 1. Left brake pedal 3. Master cylinder 2. Right brake pedal MASTER CYLINDER (BHL) Identify the brake hydraulic In Backhoe Loader (BHL) applications, there is a left brake pedal (1) and a right system on a Backhoe Loader brake pedal (2). Each pedal is connected via linkage to a master cylinder (3). (BHL). The left and right brake pedals can be connected by a lock bar (not visible). The lock bar allows both brake pedals to be applied together when locked or applied separately when unlocked. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -15- Module 1 - Hydraulic Brake Systems MASTER CYLINDER (BHL) (CONT.) 1 2 4 5 7 6 10 3 9 8 15 1. Supply port 6. Valve stem 2. Spring chamber 7. Push rod 3. Supply line 8. Compensation valve 4. Spring 9. Bridge pipe 5. Plunger 10. Compensation valve Master Cylinder (BHL) (cont.) Using a sectional view, identify In the sectional view, fluid from the brake reservoir enters each master cylinder the components and explain the through the supply port (1) and fills the spring chamber (2) and supply line (3) to operation of the master cylinder the brakes. The spring (4) holds the plunger (5) and the valve stem (6) in a on a Backhoe Loader (BHL). NEUTRAL position. The sectional view shows the bottom master cylinder in the ENGAGED position. When one brake pedal is depressed, the push rod (7) moves against the plunger. The plunger moves to the left and trapped oil inside the plunger moves the valve stem to the left. The valve stem blocks the supply port and oil pressure in the spring chamber increases. The oil flows through the supply line to the brake piston to engage the brakes. The pressure increase unseats the compensation valve (8). Oil flows through the bridge pipe (9) to the other master cylinder. If the other brake is not engaged, the compensation valve (10) in the other master cylinder will block the oil. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -16- Module 1 - Hydraulic Brake Systems When both brakes are engaged, the compensation valve in each master cylinder opens. The two spring chambers are linked and the pressure equalizes. Brake engagement is equal on both sides. When the brakes are released, the spring in the master cylinder moves the valve stem away from the inlet port. The spring force pushes the plunger back and the pressure equalizes again. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -17- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYLINDER REVIEW 2 1 Backhoe Loader 3 4 17 1. Service brake pedals 3. Rear axle 2. Master cylinders 4. Pilot accumulator BOOSTED MASTER CYLINDER REVIEW Identify a hydraulic boosted Some machines are equipped with a hydraulic boosted brake system. Oil from a brake system on a Backhoe hydraulic circuit such as the pilot hydraulic system is used to boost the master Loader (BHL). cylinder’s force when the brakes are applied. The hydraulic force multiplies the pedal effort so the operator can obtain increased braking force with less effort. This example shows a brake hydraulic system with a boosted master cylinder and two service brake pedals (1). The service brake pedals control the brake master cylinders (2), which send oil under pressure to the brake pistons located in the rear axle (3). A hydraulic pump is used to supply oil to the boosted master cylinder, via the pilot accumulator (4). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -18- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYLINDER OPERATION (BHL) 6 5 2 1 7 4 3 8 9 18 1. From pilot accumulator 6. Large spring chamber 2. Brake spool 7. Secondary piston spring chamber 3. Feedback spring 8. Check valve 4. Primary piston 9. Brake assemblies 5. Feedback spring chamber BOOSTED MASTER CYLINDER OPERATION (BHL) Explain the boosted master The boosted master cylinder in the BHL uses oil from the pilot accumulator (1) to cylinder operation on a Backhoe provide a hydraulic boost to the master cylinder. The hydraulic force multiplies the Loader (BHL). pedal effort allowing the operator more braking force with less effort. In this illustration both brake pedals are released, and the brake spool (2) is held closed by the feedback spring (3). In the closed position, the brake spool blocks pilot oil from flowing to the primary piston (4). The feedback spring chamber (5) and the large spring chamber (6) are also open to the tank. The oil is free to flow between the large spring chamber and the secondary piston spring chamber (7). The check valve (8) is unseated. The secondary piston spring chamber is connected by lines to the brake assemblies (9). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -19- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYL OPER (CWL) BRAKES REL 7 3 4 6 1 5 2 9 8 910 Wheel Loader Brakes RELEASED 19 1. Master cylinder 6. Power cylinder 2. Hydraulic pump 7. Reservoir inlets 3. Plunger 8. Front brakes 4. Load feedback piston 9. Rear brakes 5. Servo piston BOOSTED MASTER CYLINDER OPERATION (CWL) - BRAKES RELEASED Explain the boosted master The CWL uses a hydraulically assisted master cylinder (1) that receives oil flow cylinder operation on a Compact (boost oil) from a hydraulic pump (2) via a flow control valve. When the brake pedal Wheel Loader (CWL) with the is not depressed, springs keep the components in the neutral position. Inlet oil fills brakes RELEASED. the chamber between the plunger (3) and the load feedback piston (4). The remaining inlet oil flows around the servo piston (5) and returns to the tank through the spring chamber of the power cylinder (6). Both spring chambers in the master cylinder are open to the reservoir (7). The master cylinder provides oil to the front brakes (8) and rear brakes (9). The pressure is equalized and the brake lines are full. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -20- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYL OPER (CWL) BRAKES ENG 11 5 9 8 14 4 7 10 6 1 2 3 13 12 910 Wheel Loader Brakes ENGAGED 20 1. Servo piston 8. Load feedback piston 2. Tank return port 9. Relief valve 3. Hydraulic pump 10. Secondary piston 4. Power piston 11. Reservoir inlets 5. Plunger 12. Front brakes 6. Primary piston 13. Rear brakes 7. Master cylinder 14. Power cylinder BOOSTED MASTER CYLINDER OPERATION (CWL) - BRAKES ENGAGED Explain the boosted master For the CWL, when the brake pedal is depressed, the servo piston (1) moves to the cylinder operation on a Compact left and restricts inlet oil flow to the tank return port (2). Wheel Loader (CWL) with the brakes ENGAGED. Inlet (boost) oil from the hydraulic pump (3) flows to the power piston (4). Pressure increases behind the power piston to assist the servo piston in pushing the plunger (5). The plunger acts on the primary piston (6) in the master cylinder (7). The pressure behind the power piston is also open to the load feedback piston (8) to give feedback to the operator. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -21- Module 1 - Hydraulic Brake Systems The relief valve (9) limits the amount of pressure behind the power piston. The primary piston is mechanically connected to the secondary piston (10). As the plunger pushes the primary piston and the secondary piston, they block the reservoir inlets (11). Pressure builds in the master cylinder spring chambers and at the brakes. The pressure in the spring chamber for the front brakes (12) is felt on the face of the secondary piston. This causes pressure in the rear brakes (13) to increase to the same pressure as the front brakes. When the brakes are released, the servo piston shifts back to the original position, inlet oil flows around the servo piston to the tank return passage and springs return the components to the original positions. NOTE: Callouts in the illustration not mentioned in text explanations, and those in subsequent illustrations, are shown for reference purposes only. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -22- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYL OPER (TH) BRAKES REL 7 3 4 5 6 8 13 2 9 12 10 1 11 Telehandler Brakes RELEASED 22 1. Boost cylinder 8. Primary plunger line 2. Hydraulic pump 9. Primary plunger 3. Spring 10. Power piston 4. Plunger 11. Boost cylinder plunger 5. Master cylinder 12. Valve 6. Valve 13. Brake lines 7. Reservoir BOOSTED MASTER CYLINDER OPERATION (TH) - BRAKES RELEASED Explain the boosted master The Telehandler (TH) uses a hydraulically assisted master cylinder with a separate cylinder operation on a boost cylinder (1) that receives oil flow from a hydraulic pump (2) via the pilot oil Telehandler (TH) with the system. brakes RELEASED. When the brake pedal is not depressed, the spring (3) keeps the plunger (4) in the master cylinder (5) in the neutral position. The valve (6) at the end of the master cylinder is not seated. The oil in the reservoir (7) is open to the spring chamber of the master cylinder and to the primary plunger line (8). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -23- Module 1 - Hydraulic Brake Systems When the primary plunger line is filled with oil from the brake reservoir, the line is not pressurized. The springs keep the primary plunger (9), power piston (10), and boost cylinder plunger (11) in the neutral position. The valve (12) at the end of the boost cylinder is not seated. The oil in the reservoir is open to the spring chamber of the boost cylinder and the brake lines (13). The pressure is equalized and the brake lines are full. When the brake pedal is not depressed, the spring keeps the power piston shifted against the right end of the boost cylinder. The primary plunger blocks the inlet oil. The inlet oil cannot enter the brake valve. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -24- Module 1 - Hydraulic Brake Systems BOOSTED MASTER CYL OPER (TH) BRAKES ENG 5 6 2 1 3 4 7 13 9 12 11 10 8 13 Telehandler Brakes ENGAGED 24 1. Push rod 8. Boost cylinder 2. Master cylinder plunger 9. Primary plunger 3. Master cylinder 10. Power piston 4. Valve 11. Boost cylinder plunger 5. Reservoir 12. Valve 6. Spring chamber 13. Chamber 7. Primary plunger line 14. Brake lines BOOSTED MASTER CYLINDER OPERATION (TH) - BRAKES ENGAGED Explain the boosted master For a TH, at the start of brake engagement, the push rod (1) moves the master cylinder operation on a cylinder plunger (2) to the left and oil is compressed in the master cylinder (3). The Telehandler (TH) with the compressed oil closes the valve (4) at the left end of the master cylinder. This seals brakes ENGAGED. off the passage between the reservoir (5) and the spring chamber (6) on the left end of the master cylinder. Pressure is felt in the primary plunger line (7). In the boost cylinder (8), the oil shifts the primary plunger (9), the power piston (10), and the plunger (11). Oil compressed in the boost cylinder plunger closes the valve (12) at the left end of the boost cylinder. This seals off the passage between the reservoir and the spring chamber on the left end of the boost cylinder. As the boost cylinder plunger moves, pressure begins to build and engages the brakes. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -25- Module 1 - Hydraulic Brake Systems As the primary plunger moves to the left, a passage opens allowing inlet oil to enter and flow to the right end of the power piston. Pressurized oil fills the chamber (13) behind the power piston. The oil pressure behind the power piston assists the primary plunger in pushing the power piston. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -26- Module 1 - Hydraulic Brake Systems HYDRAULIC ACCUMULATOR BRAKE SYS REVIEW 5 4 6 1 3 2 6 972M Wheel Loader 26 1. Hydraulic pump 4. Service brake control valve 2. Brake accumulators 5. Brake pedal 3. Brake charging valve 6. Service brakes HYDRAULIC ACCUMULATOR BRAKE SYSTEM REVIEW Identify the components in the In some wheel loader hydraulic accumulator brake systems, a hydraulic pump (1) hydraulic accumulator brake supplies the oil for the brake system. system on a 972M Wheel Loader. The pump oil flows to the brake accumulators (2) through a brake charging valve (3), which is used to control the amount of oil flowing into the accumulators. The accumulators contain a pre-charge of dry nitrogen. The pressurized oil works against the piston, which results in high oil pressure that flows to the service brake control valve (4). The brake pedal (5) is connected to the service brake control valve. When the operator depresses the brake pedal, the service brake control valve directs the oil from the accumulators to the service brakes (6), which slow or stop the machine. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -27- Module 1 - Hydraulic Brake Systems BRAKE CHARGING VALVE (CUT-IN) 7 8 2 9 5 3 6 10 4 1 11 988G Wheel Loader 27 1. Brake charging valve 7. Service brake pedal 2. Inverse shuttle valve 8. Service brake valve 3. Accumulators 9. Rear brakes 4. Check valve 10. Front brakes 5. Cut-in/cut-out spool 11. Parking brake 6. Unloading valve BRAKE CHARGING VALVE (CUT-IN) Explain the operation of the When the accumulator oil pressure decreases below the CUT-IN pressure the brake charging valve on a 988G brake charging valve (1) enters the CUT-IN mode. In the CUT-IN mode, the Wheel Loader in CUT-IN mode. combined force of the accumulator pressure and spring acting on each outer side of the inverse shuttle valve (2) is less than the high pressure in the center of the inverse shuttle valve. The center pressure moves the two halves of the inverse shuttle valve outward. This movement allows oil to flow from the accumulator charging valve to the accumulators (3). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -28- Module 1 - Hydraulic Brake Systems When the accumulator charging valve is connected to the accumulators, the pressure decreases between the inverse shuttle valve and the check valve (4). When the pressure to the left of the cut-in/cut-out spool (5) decreases, the spring force moves the cut-in/cut-out spool to the left. Pump pressure is directed through the cut-in/cut-out spool to the left end of the unloading valve (6). The pump pressure and spring force hold the unloading valve to the right. In this position, the orifice in the unloading valve restricts the flow to the tank. Pump oil flows to the accumulators until the accumulator pressure and the pressure at the inverse shuttle valve reaches CUT-OUT pressure. When the service brake pedal (7) is depressed, the service brakes are ENGAGED. The movement of the brake pedal is mechanically transmitted to the service brake valve (8), which directs oil to the rear brakes (9) and front brakes (10). If the machine loses power or if the hydraulic pump fails, the service brakes can still be ENGAGED. The pressure in the accumulators permits several applications of the service brakes to stop the machine or slow the machine enough to engage the parking brake (11). Caterpillar: Confidential Yellow SERVxxxx - 12/24 -29- Module 1 - Hydraulic Brake Systems BRAKE CHARGING VALVE (CUT-OUT) 6 7 2 8 3 1 4 9 5 10 11 988G Wheel Loader 29 1. Accumulators 7. Service brake valve 2. Inverse shuttle valve 8. Rear brakes 3. Cut-in/cut-out spool 9. Front brakes 4. Unloading valve 10. Brake charging valve 5. Check valve 11. Parking brake 6. Service brake pedal BRAKE CHARGING VALVE (CUT-OUT) Explain the operation of the When the pressure in the accumulators (1) increases to the CUT-OUT pressure, brake charging valve on a 988G the combined forces of the oil pressure and the spring on the outer ends of the Wheel Loader in CUT-OUT mode. inverse shuttle valve (2) overcome the force of the oil pressure on the inside of the inverse shuttle valve. The inverse shuttle valve moves and blocks the flow of oil to the accumulators. When the flow to the accumulators is blocked, the supply pressure increases. The increased pressure against the left end of the cut-in/ cut-out spool (3) overcomes the force of the spring and moves the cut-in/cut-out spool to the right. The cut-in/cut-out spool opens a passage for oil on the left end of the unloading valve (4) to flow to the tank. As the pressure on the left end of the unloading valve decreases, the pressure on the right end of the valve moves the valve to the left against the spring force. When the unloading valve moves to the left, pump oil flows through the unloading valve to the tank. The check valve (5) prevents the high pressure oil in the passages to the cut-in/cut-out spool and the inverse shuttle valve from flowing back to the tank. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -30- Module 1 - Hydraulic Brake Systems The accumulator charging valve will remain in the CUT-OUT mode until the pressure in one of the accumulators decreases to the CUT-IN pressure. When the brake pedal (6) is RELEASED, spring force at the bottom of the service brake valve (7) moves the brake spools up and the service brake valve blocks oil flow to the rear brakes (8) and front brakes (9). Oil in the rear and front brakes flows through the service brake valve to the tank. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -31- Module 1 - Hydraulic Brake Systems ACCUMULATOR CHARGING (LWL) 1 4 4 2 1 2 3 3 992G Large Wheel Loader 992G Large Wheel Loader Low Pressure / CUT-IN High Pressure / CUT-OUT 31 1. Pump servo valve 3. Swashplate 2. Control spring 4. Control piston ACCUMULATOR CHARGING (LWL) Explain the accumulator charging In Large Wheel Loader (LWL) applications, a variable hydraulic pump and pump operation in Large Wheel Loader servo valve (1) control the amount of oil flowing into the accumulators, rather than a (LWL) applications. brake charging valve. When the engine is running, the brake pump maintains the oil pressure in the brake accumulators at a constant range while the engine is running. When pressure in the brake system is less than the accumulator cut-in pressure, the control spring (2) keeps the swashplate (3) at maximum angle and pump displacement is maximum. A spool in the servo valve blocks the flow of oil to the control piston (4). When the brake system pressure reaches the accumulator cut-out pressure, oil from the servo valve moves the control piston against the control spring. This movement decreases the swashplate angle and pump displacement to maintain the specified system pressure. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -32- Module 1 - Hydraulic Brake Systems COMBINATION VALVE (MG) 4 A1 A2 10 1 T 5 6 3 9 8 2 P F 7 1 120GC Motor Grader 32 1. Combination valve 6. Cut-in/cut-out spool 2. Priority valve 7. Relief valve 3. Pump 8. Orifice 4. Brake accumulators 9. Check valve 5. Fan motor 10. Pressure switch COMBINATION VALVE (MG) Explain the combination valve In Motor Grader (MG) applications, the combination valve (1) operates the same as operation in Motor Grader the charging valve but replaces the flow control valve with a priority valve (2). The applications. priority valve directs oil flow from the pump (3) to either the brake accumulators (4) or to another hydraulic system, such as a fan motor (5), before it returns to the tank. The priority valve ensures the brake hydraulic system always has oil priority over the other hydraulic systems. Oil flow from the pump into the combination valve is regulated by the priority valve. The cut-in/cut-out spool (6) shifts when the accumulator pressure has reached the cut-out pressure and allows the priority valve to send excess oil to the other hydraulic systems. The priority valve is preset to provide most of the oil flow from the pump to the brake system until the accumulator charge pressure has been attained. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -33- Module 1 - Hydraulic Brake Systems The relief valve (7) limits the oil pressure in the combination valve circuit. The orifice (8) removes pump pressure spikes and the check valve (9) maintains the brake charge pressure. A pressure switch (10) may be included in the circuit to alert the operator of low brake oil pressure. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -34- Module 1 - Hydraulic Brake Systems COMBINATION VALVE (MWL) 3 10 10 6 2 1 8 1 10 9 9 4 7 2 4 8 5 950M Wheel Loader 34 1. Brake charging solenoid valve 6. Fan motor 2. Combination valve 7. Pressure reducing valve 3. Brake accumulators 8. Fan solenoid valve 4. Priority valve 9. Pressure reducing valve 5. Pump 10. Brake pressure sensors COMBINATION VALVE (MWL) Explain the combination valve In Medium Wheel Loader (MWL) applications, brake accumulator charging is operation in Medium Wheel controlled by an ECM, which sends current to the brake charging solenoid Loader applications. valve (1). The brake solenoid valve, located in the combination valve (2), replaces the cut-in/cut-out valve and controls the oil flow to the brake accumulators (3). The priority valve (4) directs oil flow from the pump (5) to the brake accumulators or to the fan system before it returns to the tank. The priority valve ensures the brake hydraulic system always has oil priority over the fan system. Oil to the fan motor (6) is controlled by a pressure reducing valve (7) and fan solenoid valve (8) contained in the combination valve. This combination valve also provides oil flow for the steering and implement pilot systems, via a pressure reducing valve (9). Brake pressure sensors (10) alert the operator of low brake oil pressure. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -35- Module 1 - Hydraulic Brake Systems SYSTEMS TESTING AND ADJUSTING OVERVIEW 35 SYSTEMS TESTING AND ADJUSTING OVERVIEW Give an overview of testing Brake system testing may need to be performed to troubleshoot a brake system and adjusting procedures for problem or to optimize the performance of a machine’s braking system such as hydraulic brake systems. during a Technical Analysis 2 (TA2) inspection. A TA2 inspection may be performed annually or when necessary to restore equipment back to the factory performance specifications. This section identifies and describes the common brake system operational and pressure tests that are routinely performed to troubleshoot a problem or during a TA2 inspection. After completing this section, you should be able to: Identify brake system pressure test locations. Describe brake system test procedures. Describe brake system adjusting procedures. NOTE: TA2 inspection forms can be located in the Service Information System (SIS) or at https://dealer.cat.com. Refer to the appropriate Testing and Adjusting manual for all of the brake system testing procedures specific to the machine being serviced. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -36- Module 1 - Hydraulic Brake Systems OPERATIONAL CHECKS: BRAKE HOLDING TESTS Service Brake Parking Brake 36 OPERATIONAL CHECKS: BRAKE HOLDING TESTS Explain the general procedure The brake holding tests will determine if the service brakes and parking brake are for performing the service brake operating within specification. The general procedure is similar for machines with and parking brake holding ability wheels that turn or machines that articulate to turn. tests. If the machine moved during either brake test, further inspection and testing may be required. Service Brake Holding Ability Test The general procedure for the service brake holding ability test involves: 1. Start the engine, raise the implement slightly, and release the parking brake. 2. Put the transmission control in the gear, specified by the Operation and Maintenance Manual, while the service brakes are applied. 3. Increase the engine speed to high idle. The machine should not move. 4. Reduce the engine speed to low idle and move the transmission direction control to the NEUTRAL position. Engage the parking brake. Lower the implement to the ground. Stop the engine. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -37- Module 1 - Hydraulic Brake Systems Parking Brake Holding Ability Test The general procedure for the parking brake holding ability test involves: 1. Start the engine, raise the implement slightly, and engage the parking brake. 2. Ensure that the transmission control is in the MANUAL position. 3. Put the transmission control in the gear specified by the Operation and Maintenance Manual. The parking brake indicator light should illuminate. 4. Increase the engine speed to high idle. The machine should not move. 5. Reduce the engine speed to low idle and move the transmission direction control to the NEUTRAL position. Lower the implement to the ground and stop the engine. NOTE: Carry out all the necessary safety checks/precautions/procedures before attempting any task. Refer to the appropriate service literature when performing the brake holding tests. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -38- Module 1 - Hydraulic Brake Systems BRAKE ACCUM CHECK: HYD ACCUM BRAKE SYS 2 1 38 1. Alert indicator 2. Service brake pedal BRAKE ACCUMULATOR CHECK: HYDRAULIC ACCUMULATOR BRAKE SYSTEMS Explain the general procedure The brake accumulator check will determine if the accumulator pre-charge pressure for performing the brake is within specifications. accumulator check. The general procedure for a brake accumulator check involves: 1. Turn the engine start switch to the ON position. The alert indicator (1) should illuminate if the braking system is not at normal operating pressure. 2. Start the engine and run at low idle speed until the engine is warm to increase the accumulator pressure. The alert indicator should go off. 3. At low idle, fully depress the brake pedal (2) and release. Repeat this process until hearing the brake charging system recharge the accumulators. When charging, there should be a slight decrease in engine rpm. 4. When charging is completed, stop the engine and turn the key to the ON position without starting the engine. Fully apply the brake pedal and fully release the brake pedal at a rate of one second ON and one second OFF. Count the number of cycles until the brake oil pressure alert indicator comes on. A minimum number of applications of the brake pedal are required as specified by the Operation and Maintenance Manual. 5. If the alert indicator comes on before the number of cycles listed in step 4, measure the accumulator pre-charge pressures and recharge as necessary. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -39- Module 1 - Hydraulic Brake Systems ACCUMULATOR PRESSURE 175-5507 Nitrogen Charging Group 39 ACCUMULATOR PRESSURE Explain the general procedure The brake accumulator should be charged if the accumulator has less than half of to check and charge a brake the required amount of precharge pressure. accumulator. The general procedure to check and charge a brake accumulator involves: 1. Ensure all pressure has been released from the hydraulic system. 2. Install the nitrogen charging group (per the Testing and Adjusting manual) at the nitrogen charging valve (arrow). 3. Record the charge pressure in the accumulator. 4. If the accumulator pressure is not within specification, charge the accumulator to obtain the correct pressure. 5. Allow the accumulator temperature to stabilize. Recheck the precharge pressure at the stabilized temperature. The test can be performed using the 175-5507 Nitrogen Charging Group tool. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -40- Module 1 - Hydraulic Brake Systems SERVICE BRK PRES TEST: MASTER CYL BRAKE SYS 1 2 40 1. Master cylinder test port 2. Brake pedal SERVICE BRAKE PRESSURE TEST: MASTER CYLINDER BRAKE SYSTEM Explain the general procedure to The service brake pressure test measures the oil pressure in the service brake check the service brake pressure circuit. on machines equipped with a master cylinder. The general procedure to check the service brake pressure on machines equipped with a master cylinder involves: 1. Install the appropriate pressure gauge (per the Testing and Adjusting manual) at the master cylinder test port (1). 2. Start the engine. 3. Release the parking brake. 4. Press the brake pedal (2) until the pressure reaches the correct specification. 5. Record the pressure reading on the pressure gauge. If the pressure is not within specification further brake system testing and inspection may be required. NOTE: If the machine is equipped with a boosted master cylinder and the service brake pressure is not within specification check the input (boost) oil pressure. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -41- Module 1 - Hydraulic Brake Systems SERVICE BRK PRES: HYD ACCUM BRAKE SYSTEM 2 1 41 1. Rear service brake pressure test port 2. Front service brake pressure test port SERVICE BRAKE PRESSURE: HYDRAULIC ACCUMULATOR BRAKE SYSTEM Explain the general procedure to The general procedure to check the service brake pressure involves: check the service brake pressure on a hydraulic accumulator brake 1. Stop the engine. Place the transmission direction selector in the NEUTRAL system. position and engage the parking brake. 2. Depress the brake pedal repeatedly to release all oil pressure from the brake circuit. 3. Install a pressure gauge at the rear service brake pressure port (1). 4. Start the engine and allow the hydraulic oil to reach normal operating temperature and normal operating pressure. 5. Hold down the brake pedal and record the brake pressure. 6. If the brake pressure is not in the correct range but the brake accumulator charging valve is functioning correctly, replace the brake control valve. 7. Repeat this procedure at pressure port (2) to test the oil pressure at the front service brakes. NOTE: Some machines may be equipped with a pressure test port near the wheels so that pressure can also be checked at the inlet to the brake pistons. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -42- Module 1 - Hydraulic Brake Systems ACCUM PRESSURE (CUT-IN/CUT-OUT) TEST 950M Wheel Loader 950G Wheel Loader 120GC Motor Grader 1 2 2 2 1 1 198-4240 Digital Pressure Indicator Group 42 1. Accumulator pressure port 2. Accumulator charging valve ACCUMULATOR PRESSURE (CUT-IN/CUT-OUT) TEST Explain the general procedure to The general procedure to check the accumulator pressure involves: check the accumulator pressure (cut-in/cut-out test). 1. Stop the engine. Place the transmission direction selector in the NEUTRAL position and engage the parking brake. 2. Depress the brake pedal repeatedly to release all oil pressure from the brake circuit. 3. Install a pressure gauge at the accumulator pressure port (1) on the accumulator charging valve (2). 4. Start the engine and operate the engine at HIGH IDLE. 5. Record the highest accumulator pressure reading, which is the accumulator cut-out pressure. 6. Apply the service brakes several times in succession and verify that the pressure drops consistently. At the lowest pressure (cut-in) the oil pressure should begin to increase quickly. 7. Record the lowest accumulator pressure reading, which is the cut-in pressure. 8. If the cut-out or cut-in pressure is not in the correct range adjust the accumulator charging valve or replace the valve. The test can be performed using the 198-4240 Digital Pressure Indicator Group tool. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -43- Module 1 - Hydraulic Brake Systems ACCUMULATOR BRAKE PRESSURE ADJUSTMENT 1 1 2 43 1. Plug 2. Adjustment screw ACCUMULATOR BRAKE PRESSURE ADJUSTMENT Explain the general procedure to The general procedure to adjust the accumulator pressure involves: adjust the accumulator pressure. 1. Stop the engine and completely release all oil pressure from the brake circuit by depressing the brake pedal repeatedly and loosen the hydraulic tank filler cap to make sure that there is no residual pressure in the hydraulic oil tank. 2. Remove the plug (1) to access the adjustment screw (2). Turn the adjustment screw clockwise to increase the cut-in and cut-out pressure and counterclockwise to decrease the cut-in and cut-out pressure. 3. Start the engine and ensure sure that the cut-in and cutout pressures are within specifications. 4. If the pressures are not within specification, the brake accumulator charging valve should be repaired or replaced. NOTE: The charging cut-out and cut-in pressure limits change together. The range between cut-in and cutout pressure is not adjustable. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -44- Module 1 - Hydraulic Brake Systems PARKING BRAKE PRESSURE 2 1 44 1. Parking brake pressure port 2. Parking brake valve PARKING BRAKE PRESSURE Explain the general procedure The general procedure to adjust the parking brake pressure involves: to adjust the parking brake pressure. 1. Start the engine and allow the hydraulic oil to reach normal operating temperature and normal operating pressure. 2. Stop the engine. Place the transmission direction selector in the NEUTRAL position and engage the parking brake. 3. Install a pressure gauge at the parking brake pressure port (1) on the parking brake valve (2). 4. Start the engine and run the engine until cut-out pressure is reached. 5. Move the parking brake control switch to the OFF position. 6. With the engine running at LOW IDLE place the parking brake switch to the ON position and record the brake pressure. If the pressure is not within specification further parking brake system testing and inspection may be required. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -45- Module 1 - Hydraulic Brake Systems SYSTEM TROUBLESHOOTING OVERVIEW 45 SYSTEM TROUBLESHOOTING OVERVIEW Give an overview of To isolate the root cause of a problem, further inspection of system components troubleshooting processes for and/or system testing may be required. hydraulic brake systems. A machine that does not brake efficiently may indicate a problem in the brake system. This section identifies the component inspections, as well as the types of tests that should be performed to troubleshoot problems with the brake system. Prior to inspection and component testing, using a troubleshooting chart can help establish possible causes based on any symptoms that may have been identified. After completing this section, you should be able to: Describe the process for troubleshooting hydraulic brake system problems. Identify possible causes of a hydraulic brake issue based on given symptoms. Describe inspection procedures to find the root cause of a hydraulic brake issue. NOTE: Equipment inspections identify potential problems before failure and reduce unplanned downtime. Family and model-specific checklists have been developed for technicians and are available in SIS or at https://dealer. cat.com. TA2 inspections are either performed annually or when required. Such inspections can pinpoint problems in the brake system. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -46- Module 1 - Hydraulic Brake Systems CATERPILLAR 7-STEP DIAGNOSTIC PROCESS 46 1. Verify Customer Concern 5. Repair Root Cause 2. Conduct Initial Inspection 6. Verify the Repair 3. List Possible Causes 7. Document Concern, Analysis, Repair in Service 4. Analyze Possible Causes and Determine Report Root Cause CATERPILLAR 7-STEP DIAGNOSTIC PROCESS Using the Caterpillar 7-Step When approaching brake system service issues, a consistent diagnostic strategy Diagnostic Process, give a should be followed. summary of the steps involved for a brake system issue. The Caterpillar 7-Step Diagnostic Process involves investigating, isolating, repairing, and documenting the customer concern. Each step accumulates information that helps direct the next step. In this section, the focus will be on the Investigate and Isolate steps to identify the possible cause(s) using inspection and testing procedures. NOTE: Always refer to Caterpillar service information for the correct tests and specifications for the machine being serviced. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -47- Module 1 - Hydraulic Brake Systems Caterpillar 7-Step Diagnostic Process 1. Verify Customer Concern: If a customer is concerned about erratic brake operation, make a visual inspection to identify symptoms that could indicate the brake system is the cause. 2. Conduct Initial Inspection: During the inspection, look for signs of any external leaks. Check the hydraulic oil level. Finally, look for signs of damage to any of the brake system components. 3. List Possible Causes: The results of Steps 1 and 2 will guide development of a list of possible causes. This might include oil restrictions or leaks somewhere in the brake hydraulic system. 4. Analyze Possible Causes and Determine Root Cause: Determining the root cause may involve performing tests to determine hydraulic oil pressure. Test results may require closer examination of components and fittings for leaks, cracks, or failures. 5. Repair Root Cause: When repairing the root cause of the concern, remember the brake hydraulic system must maintain proper oil pressure to perform correctly. 6. Verify the Repair: When verifying repairs to the brake system, always check for the correct oil level. Then, ensure there are no external leaks. Finally, measure the oil pressure and compare the results to TMI specifications. 7. Document Concern, Analysis, Repair in Service Report: To properly document the repair, describe the concern, root cause, service details, and part number (if applicable). Any additional information that might be helpful in future analysis or repairs should also be included. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -48- Module 1 - Hydraulic Brake Systems INITIAL INSPECTION 1 2 3 4 Master Cylinder Brake System 2 5 8 7 3 3 6 Hydraulic Accumulator Brake System 48 1. Master cylinder 5. Service brake control valve 2. Brake lines and fittings 6. Brake accumulators 3. Brake assemblies 7. Accumulator charging valve 4. Hydraulic (boost) oil source 8. Hydraulic (pump) oil source INITIAL INSPECTION Identify the steps in an initial Performing an external inspection of the brake system occurs during the initial inspection. inspection, after the customer concern has been verified. Prior to the inspection, lower the implements to the ground and then stop the engine. Machines with a Master Cylinder Brake System Check the following components for damage and leaks: Master cylinder (1) Brake lines and fittings (2) Brake assemblies (3) Hydraulic (boost) oil source (4) Caterpillar: Confidential Yellow SERVxxxx - 12/24 -49- Module 1 - Hydraulic Brake Systems Machines with a Hydraulic Accumulator Brake System Check the following components for damage and leaks: Brake lines and fittings (2) Brake assemblies (3) Service brake control valve (5) Brake accumulators (6) Accumulator charging valve (7) Hydraulic (pump) oil source (8) Caterpillar: Confidential Yellow SERVxxxx - 12/24 -50- Module 1 - Hydraulic Brake Systems SYMPTOM TROUBLESHOOTING 50 SYMPTOM TROUBLESHOOTING Review the troubleshooting A troubleshooting chart helps establish a list of possible causes based on the chart included in the Instructor symptoms that may have been identified while verifying the customer concern and Materials and Activity Workbook. conducting an initial inspection. Additionally, the Testing and Adjusting manual or Troubleshooting manual may provide probable causes to known problems, as Inform the participants that the shown in the example above. intent of the troubleshooting chart is to teach diagnostic principles. It is not intended to teach all possible symptoms, nor encourage jumping to conclusions. For additional troubleshooting details read current service information. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -51- Module 1 - Hydraulic Brake Systems MASTER CYLINDER 51 MASTER CYLINDER Identify symptoms that could Any of the following symptoms could indicate a problem with the master cylinder: indicate a problem with the master cylinder. Service brakes do not operate Service brakes are not applied evenly Too much force needed to push the brake pedal Brakes do not release The operation of a master cylinder involves sending oil under pressure to the brake pistons in the brake assemblies. Identify the test used to If the master cylinder is suspected as a possible problem, perform the Service determine if the master cylinder Brake Pressure Test: Master Cylinder Brake System covered in the System Testing is a possible problem. and Adjusting section to determine if the master cylinder could be causing the problem. If the results show that the pressure is not within specifications, then service or replace the master cylinder as needed. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -52- Module 1 - Hydraulic Brake Systems SERVICE BRAKE ASSEMBLY 52 SERVICE BRAKE ASSEMBLY Identify symptoms that could Any of the following symptoms could indicate a problem with the service brake indicate a problem with the assembly: service brake assembly. Service brakes do not operate Service brakes are not applied evenly Brake pedal is noisy Brakes slip The operation of the service brake assembly involves using friction to cause the machine to slow down and stop. Identify the test used to If the service brake assembly is suspected as a possible problem, perform the determine if the service brake Service Brake Holding Ability Test covered in the System Testing and Adjusting assembly is a possible problem. section. If the machine moved during the service brake test, then inspect the service brake components for damage and excessive wear. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -53- Module 1 - Hydraulic Brake Systems BRAKE CHARGING VALVE 53 BRAKE CHARGING VALVE Identify symptoms that could Any of the following symptoms could indicate a problem with the brake charging indicate a problem with the brake valve assembly: charging valve assembly. Service brakes do not operate Too much force needed to push the brake pedal Only one or two brake pedal applications between cut-out and cut-in The operation of the brake charging valve involves controlling the oil flow to the brake accumulators to keep them properly charged. Identify the test used to If the brake charging valve is suspected as a possible problem, perform the determine if the brake charging Accumulator Pressure Test covered in the System Testing and Adjusting section to valve is a possible problem. determine if the brake charging valve could be causing the problem. If the results show that the pressures are not within specifications, then service (adjust) or replace (if non-adjustable) the brake charging valve as needed. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -54- Module 1 - Hydraulic Brake Systems BRAKE ACCUMULATORS 54 BRAKE ACCUMULATORS Identify symptoms that could Any of the following symptoms could indicate a problem with the brake indicate a problem with the brake accumulators: accumulators. Service brakes do not operate Too much force needed to push the brake pedal Only one or two brake pedal applications between cut-out and cut-in The brake accumulators pressurize the hydraulic oil for brake application. Identify the test used to If the brake accumulators are suspected as a possible problem, perform the Brake determine if the brake Accumulator Check Procedure covered in the System Testing and Adjusting section accumulators are a possible to determine if the accumulators are charged. problem. Charge the accumulators to the specified pressure if necessary. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -55- Module 1 - Hydraulic Brake Systems SERVICE BRAKE CONTROL VALVE 55 SERVICE BRAKE CONTROL VALVE Identify symptoms that could Any of the following symptoms could indicate a problem with the service brake indicate a problem with the control valve: service brake control valve. Service brakes do not operate Service brakes are not applied evenly Too much force needed to push the brake pedal Brakes do not release The operation of a service brake control valve involves sending oil under pressure to the brake pistons in the brake assemblies. Identify the test used to If the service brake control valve is suspected as a possible problem, perform the determine if the service brake Service Brake Pressure Test: Hydraulic Accumulator Brake System covered in the control valve is a possible System Testing and Adjusting section to determine if the service brake control valve problem. could be causing the problem. If the results show that the pressure is not within specifications, then service or replace the service brake control valve as needed. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -56- Module 1 - Hydraulic Brake Systems PARKING BRAKE CONTROL VALVE 56 PARKING BRAKE CONTROL VALVE Identify symptoms that could Any of the following symptoms could indicate a problem with the parking brake indicate a problem with the control valve: parking brake control valve. Parking brakes do not engage Parking brakes do not release The operation of a parking brake control valve involves controlling the oil to engage or release the parking brakes. Identify the test used to If the parking brake control valve is suspected as a possible problem, perform the determine if the parking brake Parking Brake Pressure Test covered in the System Testing and Adjusting section control valve is a possible to determine if the parking brake control valve could be causing the problem. problem. If the results show that the pressure is not within specifications, then service or replace the parking brake control valve as needed. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -57- Module 1 - Hydraulic Brake Systems PARKING BRAKE ASSEMBLY 57 PARKING BRAKE ASSEMBLY Identify symptoms that could The following symptom could indicate a problem with the parking brake assembly: indicate a problem with the parking brake assembly. Parking brakes do hold the machine stationary The operation of the parking brake assembly involves using friction to hold the machine stationary. Identify the test used to If the parking brake assembly is suspected as a possible problem, perform the determine if the parking brake Parking Brake Holding Ability Test covered in the System Testing and Adjusting assembly is a possible problem. section. If the machine moved during the parking brake test, then inspect the parking brake components for damage and excessive wear. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -58- Module 1 - Hydraulic Brake Systems PURPOSE REVIEW This module covers hydraulic brake system components, operation, testing, and troubleshooting procedures for machines equipped with hydraulic brake systems. 58 PURPOSE REVIEW Explain the purpose of this This module covers hydraulic brake system components, operation, testing, and module. troubleshooting procedures for machines equipped with hydraulic brake systems. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -59- Module 1 - Hydraulic Brake Systems REASON REVIEW Successful completion validates the knowledge, skills, and behaviors that are required to properly diagnose and repair hydraulic brake systems used in Cat machines. 59 REASON REVIEW Explain the reason for this Successful completion validates the knowledge, skills, and behaviors that are module. required to properly diagnose and repair hydraulic brake systems used in Cat machines. Caterpillar: Confidential Yellow SERVxxxx - 12/24 -60- Module 1 - Hydraulic Brake Systems ASSESSMENT CRITERIA REVIEW Knowledge Assessment Closed book Minimum passing score of