OTTAWA TRUCK SERVICE MANUAL AIR BRAKE SYSTEM TABLE OF CONTENTS Introduction Page 3 Typical Air System With ABS Page 4 Typical Air System Without ABS Page 5 Air Brake System Page 6 Trouble-shooting Guide Page 24 Print This File Return to Menu Revised 11/15/99 1
A IR B RAKE S YSTEM Revised 11/15/99 2
Introduction The air system is a vital part of the Ottawa yard tractor. Its proper functioning is necessary to operate the truck in a safe, dependable manner. The information in this section is intended to provide the service technician with a basic understanding of the air system. There are two air systems that are commonly used. One is used for trucks that must comply with FMVSS 121 and will be capable of operating on-highway.
TRACTOR PARK (YELLOW) SPRING DEL DEL INTER-AXLE LOCKOUT SUP CON DEL SUP 5TH WHEEL UNLATCH DEL (BLUE) TO AIR WIPER SUP TRACTOR PROTECTION VALVE REAR FRONT BRAKE BRAKE TANK TANK ABS VALVE SPRING BOOM (RED) DEL FIREWALL RECESS PANEL SERVICE SERVICE 5TH WHEEL UNLATCH TRAILER PARK (RED) ABS VALVE DEL REAR BRAKES RESV SUP 1 WAY CHECK VALVE SUP BA L Revised 11/15/99 QUICK RELEASE VALVE PRESSURE RELIEF VALVE DEL SER SUP DEL CON PRIMARY RESV DEL CON OPTIONAL AIR DRYER UNL
SERVICE TRACTOR PARK (YELLOW) TRAILER PARK (RED) SPRING DEL DEL SUP DEL SUP 5TH WHEEL UNLATCH (RED) DEL (BLUE) S TRACTOR PROTECTION BRAKE TANK E 5TH WHEEL UNLATCH SUP PRESSURE RELIEF CHECK VALVE AIR SEAT QUICK RELEASE VALVE DRAIN VALVE SUP DEL OPTIONAL AIR DRYER CON Revised 11/15/99 SUPPLY RESERVOIR QUICK RELEASE VALVE UNL RESV AIR COMP.
Air Brake System Components • • • • Air compressor Governor Air dryer (optional) Reservoirs Primary Front Rear Low pressure indicator Pressure relief valve Check valve • Brake valve (treadle) • Stoplight switch • Front brake chamber • • • • • • • • • Rear brake chamber Quick release valve Double check and quick release valve Slack adjusters (automatic) Air control valve Brake Trailer/Emergency Tractor protection valve Pressure protection valve Bobtail proportioning relay valve Antilock modulator valve E
Air Brake System Governor The governor (D2) is mounted on the compressor. It operates in conjunction with the compressor unloading mechanism and maintains reservoir air pressure between a predetermined maximum and minimum pressure. Reservoir air pressure enters the governor at its reservoir connect port and acts on the piston and inlet/exhaust valve. As the air pressure builds up, the piston and valve move together against the resistance of the pressure setting spring.
Air Brake System OPERATION: When air pressure at the supply port and under the diaphragm is above 70 psi, the electrical contacts remain open because the force exerted by air pressure underneath the diaphragm overcomes the force exerted by the spring above the diaphragm. When air pressure below the diaphragm drops below 70psi, the spring exerts a force which is greater than the force exerted by the air pressure below the diaphragm.
Air Brake System Check Valve The in-line check valve is a device placed in an air line to allow air flow in one direction only, and to prevent flow of air in the reverse direction. An arrow indicating the direction of air flow is cast into the body of the valve. OPERATION: Air flow in the normal direction moves the check valve disc from its seat, and the flow is unobstructed.
Air Brake System Balanced: No. 2 circuit portion When the air pressure on the No. 2 side of the relay piston approaches that being delivered on the No. 1 side of the relay piston, the relay piston moves, closing the No. 2 inlet valve and stopping further flow of air from the supply line through the valve. The exhaust remains closed as the No. 2 delivery pressure balances the No. 1 delivery pressure. When applications in the graduating range are made, a balanced position in the No.
Air Brake System Stop Light Switch The stop light switch (SL5) is an Electro-pneumatic switch and operates in conjunction with the brake valve and stoplights by completing the stop light electrical circuit when a brake application is made. When a brake application is made, air pressure from the brake valve enters the cavity below the diaphragm.
Air Brake System Double Check and Quick Release Valve (QR-1C) The Double Check and Quick Release Valve (QR-1C) is a dual function valve. The valve’s primary function is to serve the emergency side of a spring brake actuator as a quick release valve. In addition, it functions as an anti-compound device. The double check valve prevents a service and emergency brake application from occurring simultaneously. The air connectors to the valve are as follows: 1.
Air Brake System Slack Adjusters (automatic) The slack adjuster is the link between the brake chamber and the foundation brake camshaft. It transforms and multiplies the force developed by the chamber into torque, which applies the brakes via the brake camshaft. The automatic adjustment provided by the slack adjuster results in consistent brake-lining-to-drum clearance and brake actuator stroke.
Air Brake System To Park Tractor and Trailer Combination - With both controls pushed in (the normal driving mode), pulling out the (YELLOW) Parking Brake control applies BOTH the tractor and trailer spring/parking brakes. The Trailer Air Supply control (RED) will remain pushed in and will not pop out. Both the tractor and the trailer should now be parked with all spring/parking brakes applied.
Air Brake System While the BP-R1 can incorporate various crack pressures to accommodate specific applications, the standard is 4 psi. Air connections on the BP-R1 are identified with cast, embossed letters for ease of installation. The letter identification and air line connections are shown below for reference.
Air Brake System SERVICE BRAKES RELEASING Tractor/Trailer Combination When the brake application is released, air pressure in the service port of the BP-R1 returns to the foot brake valve and is exhausted. Air from above the relay piston flows back through the proportioning, blend back and service pistons to the exhaust diaphragm. If the service brakes are rapidly released, the diaphragm flexes in response to the returning air and opens the exhaust.
Air Brake System LEAKAGE TESTS 1. Build the air system pressure to governor cut-out. With the dash-mounted trailer supply valve activated for tractor/trailer operation, apply a soap solution to all three exhaust ports (two in cover and one in body). The leakage noted should not exceed a one inch bubble in less than three seconds at any exhaust port. 2. Make and hold a full brake application and apply a soap solution to all three exhaust ports and around the cover where it joins the body.
Air Brake System Antilock Operation — General If a service brake application is made and the antilock system detects an impending wheel lockup, the antilock controller will immediately begin modification of the brake application using the modulator valve. In order to modify the brake application, the coils of the two solenoid valves contained in the modulator valve are energized or de-energized in a pre-programmed sequence by the antilock controller.
Air Brake System Antilock Re-Apply If the antilock controller senses that wheel speed has increased sufficiently to require re-application of braking pressure, it de-energizes the supply and exhaust solenoids. With both solenoids de-energized, the modulator valve re-applies air to the brakes in the same manner it did during a Non-Antilock Application. E-16 Antilock Electronic Control Unit General Description The EC-16 is an electronic antilock controller.
Air Brake System Physical Description The EC-16 electronics are contained in a die-cast aluminum housing and are environmentally protected by a self-healing silicone compound. The metal housing and the design of the digital electronics are intended to provide a high degree of protection from radio and electromagnetic interference. The patented light-emitting diode (LED) display and a magnetically actuated reset switch is incorporated in the housing for troubleshooting and diagnostic purposes.
Air Brake System An antilock dashlight and its electrical relay are connected to, and controlled by, the EC-16, and serve as a means of advising the driver of the condition of the antilock system. A connection to the engine or transmission retarder and its relay is provided on the EC-16, which allows the EC-16 to temporarily disable the retarder during certain modes of operation. While the EC-1 is capable of this function and the connections are provided, it is not always used.
Air Brake System Antilock Brake Application If a service brake application is made and the wheel speed sensors detect an impending wheel lockup, the EC-16 controller will immediately begin modification of the brake application using the antilock modulator(s) at the affected wheel(s). Solenoid valves contained in the modulator are energized and de-energized by the EC-16 controller, in order to modify the brake application. When a solenoid coil is energized, its shuttle moves.
Air Brake System When the controller senses an erroneous condition, it stores the condition in memory, disables the antilock or traction function, and illuminates the dash-mounted condition lamp and appropriate diagnostic LEDs on the EC-16. The failure condition is truly stored and is not cleared by loss of power to the EC-16. The LEDs will re-light when power is restored, and remain illuminated until the failure is corrected.
Air Brake System EC-16 CONFIGURATION DISPLAY 1. Turn the ignition ON. 2. All LEDs will illuminate, then go out. Troubleshooting Guide Air Dryer Condition Possible Cause Remedy/Recommendation Air Dryer is constantly cycling or purging Excessive system leakage Check for system leakage and repair. Excessive leakage in fittings, hoses, and tubing connected to compressor, air dryer and main supply reservoir.
Air Brake System Troubleshooting Guide Air Dryer (cont’d) Condition Possible Cause Remedy/Recommendation Water in Vehicle Reservoirs Bendix air dryer desiccant cartridge requires replacement. Replace desiccant cartridge. Refer to the Medium Duty Truck Unit Repair Manual. Air system charged from an external air source. Air not passing through air dryer. Charge system from the filter valve at the air compressor so the sir must flow through the air dryer. Air dryer not purging. Check purge valve.
Air Brake System Troubleshooting Guide Air Dryer (cont’d) Condition Possible Cause Remedy/Recommendation Constant Exhaust Of Air At Air Dryer Purge Valve Exhaust Or Unable To Build System Pressure Air dryer purge valve leaking excessively. Check for excessive leakage with compressor loaded, apply soap solution on purge valve exhaust. Repair or replace air dryer. Refer to the Medium Duty Truck Unit Repair Manual. Faulty governor.
Air Brake System Troubleshooting Guide Air Dryer (cont’d) Condition Possible Cause Remedy/Recommendation Air Dryer Does Not Purge Or Exhaust Air Broken, kinked, frozen, plugged or disconnect purge control line. Test to determine air flows through purge control line when compressor is unloaded. Faulty air dryer purge valve. Repair or replace air dryer.
Air Brake System AIR LEAKAGE CHECK 1. Set the parking brake. 2. Start the engine and charge the air system to the governor cutout point. 3. Stop the engine. 4. Apply and release the service brakes. 5. Note air leakage. • Vehicles without trailer controls-The dual air pressure gauge reading should drop less than 28kPa (4 psi) in 2 minutes. • Vehicles with trailer controls-The dual air pressure gauge reading should drop less than 41 kpa (6 psi) in 2 minutes.
Air Brake System 12. On vehicles with trailer controls, move the trailer brake hand control handle clockwise to the full “ON” position. 13. Air leakage should be less than 41 kpa (6 psi) in 2 minutes. • If air leakage is more than 41 kpa (6 psi) check the airlines, trailer brake hand control valve, tractor protection valve, and any valves on the trailer. Refer to “System Schematics” for diagrams showing the parts between the tractor and the trailer or SECTION 5H to test air valves for leaks.
Air Brake System 5G-6 AIR BRAKES External Conditions That Affect Brake Performance 1. Tires — Tires with unequal contact and grip on the road will cause unequal braking. The inflation and tread pattern of the right and left tires must be about equal. 2. Vehicle Loading — When the vehicle has unequal loading, the most heavily loaded wheels require more braking force than the others. 3. Front Wheel Bearings — Loose wheel bearings permit the rotor to tilt and have spotty contact with the linings.
Air Brake System LOW AIR PRESSURE SWITCH 1. Set the parking brake. 2. Drain all air reservoirs. Refer to “Draining Air Reservoirs.” 3. Start the engine and run at a fast idle. 4. Verify that the low pressure tone alarm is on. • If the tone alarm is not on when first charging the system, check the tone alarm circuit or replace the low pressure switch as necessary. Refer to SECTION 8C to check the tone alarm circuit and “Low Air Pressure Switch” to replace the low air pressure switch. 5.
Air Brake System 8. Start the engine and charge the air system to the governor cutout point. 9. Make sure the SYSTEM PARK control, TRAILER AIR SUPPLY, and TRACTOR PARK controls are applied, if present. 10. Turn off the engine. 11. Open the drain cock and drain the front service reservoir. 12. Check if the items in Step 7 function normally. If any do not work, replace the stoplight switch. Refer to “Stoplight Switch” in “On-Vehicle Service.” 13.
